Psoriasis | Psoriatic Arthritis | MedlinePlus

Psoriasis is a skin disease that causes itchy or sore patches of thick, red skin with silvery scales. You usually get the patches on your elbows, knees, scalp, back, face, palms and feet, but they can show up on other parts of your body. Some people who have psoriasis also get a form of arthritis called psoriatic arthritis.

A problem with your immune system causes psoriasis. In a process called cell turnover, skin cells that grow deep in your skin rise to the surface. Normally, this takes a month. In psoriasis, it happens in just days because your cells rise too fast.

Psoriasis can be hard to diagnose because it can look like other skin diseases. Your doctor might need to look at a small skin sample under a microscope.

Psoriasis can last a long time, even a lifetime. Symptoms come and go. Things that make them worse include

Psoriasis usually occurs in adults. It sometimes runs in families. Treatments include creams, medicines, and light therapy.

NIH: National Institute of Arthritis and Musculoskeletal and Skin Diseases

View original post here:

Psoriasis | Psoriatic Arthritis | MedlinePlus

Psoriasis – Causes, Symptoms and Treatment – Health.com

Jump to: Types | Causes | Symptoms | Diagnosis | Treatment | Living with Psoriasis | Celebrities with Psoriasis

Psoriasis is a disease in which red, scaly patches form on the skin, typically on the elbows, knees, or scalp. An estimated 7.5 million people in the United States will develop the disease, most of them between the ages of 15 and 30. Many people with psoriasis experience pain, discomfort, and self-esteem problems that can interfere with their work and social life.

Although the exact cause of psoriasis is unknown, researchers say the disease is largely geneticits caused by a combination of genes that send the immune system into overdrive, triggering the rapid growth of skin cells that form patches and lesions.

A dermatologist can likely tell the difference between psoriasis and eczema, but to the untrained eye, these skin conditions can appear similar. Generally speaking, psoriasis appears as thick, red patches that have a scaly buildup on top, according to the American Academy of Dermatology (AAD). These lesions are usually well defined, whereas eczema tends to cause a rash and be accompanied by an intense itch.

In addition, psoriasis tends to occur on the outside of the knees and elbows, and on the lower back and scalp; eczema usually covers the elbow and knee creases and the neck or face.

Research published in 2015 in the Journal of Clinical Medicine suggested that infants and children with psoriasis may be particularly likely to be misdiagnosed with eczema because they may have less scaling than adults.

RELATED: Whats That Rash?

Back to top

Psoriasis can range in severity, from mild patches to severe lesions that can affect more than 5% of the skin. There are five types of the disease: plaque psoriasis, pustular psoriasis, guttate psoriasis, inverse psoriasis, and erythrodermic psoriasis. Some people will have one form, whereas others will have two or more.

Plaque psoriasis appears as red patches with silvery white scales, or buildup of dead skin cells, called plaques. Its the most common type of psoriasis, affecting up to 90% of all people with the disease, according to the AAD. Most often found on the scalp, elbows, lower back, and knees, the plaques themselves will be raised and have clear edges; they may also itch, crack, or bleed.

Pustular psoriasis is a form of psoriasis in which white pustules (or bumps filled with white pus) appear on the skin. In a typical cycle, the skin will turn red, break out in pustules, and then develop scales. There are three types of pustular psoriasis: von Zumbusch pustular psoriasis (which appears abruptly and can be accompanied with fever, chills, and dehydration), palmoplantar pustulosis (which appears on the soles of the feet and the hands), and acropustulosis (a rare form of psoriasis that forms on the ends of the fingers or toes).

Guttate psoriasis is a type of psoriasis that appears as red, scaly teardrop-shaped spots. (The word guttate is Latin for drop.) During a flare-up, hundreds of lesions can form on the arms, legs, and torso, although they can also appear on the face, ears, and scalp. Guttate is the second most common type of psoriasis, occurring in about 10% of all people with the disease. Its most likely to appear in people who are younger than 30, oftentimes after they develop an infection like strep throat.

Inverse psoriasis is a type of psoriasis that appears as smooth, bright red lesions in the armpit, groin, and other areas with folds of skin. Because these regions of the body are prone to sweating and rubbing, inverse psoriasis can be particularly irritating and hard to treat.

Erythrodermic psoriasis is rare but can require immediate treatment or even hospitalization. The lesions look like large sheets rather than small spots, as if the area has been burned, and tend to be severely itchy and painful. A flare-up can trigger swelling, infection, and increased heart rate.

Psoriasis is not contagiousits a genetic, autoimmune disease. Psoriasis lesions cannot infect other people; likewise, people cant catch psoriasis from someone else, whether through touching, sexual contact, or swimming in the same pool. Its unclear, however, whether a majority of the general public is aware of this fact. In a small 2015 survey in the Journal of the American Academy of Dermatology, about 60% of people said they thought that psoriasis was infectious, while 41% said they thought the lesions looked contagious.

RELATED: 14 Ways to Manage Your Psoriasis

Back to top

The simplest answer to the question of what causes psoriasis: your genetics. An estimated 10% of people inherit at least one of the genes that can cause psoriasis. (There are as many as 25 genetic mutations that make someone more likely to develop psoriasis.) But only 2% to 3% of people will develop the disease, according to the National Psoriasis Foundation (NSF). Therefore, researchers believe that psoriasis is caused by a certain combination of genes that spring into action after being exposed to a trigger. Common triggers include stress, an infection (like strep throat), and certain medications (like lithium). Cold, dry weather and sunburns may also trigger psoriasis flares.

When someone with psoriasis is exposed to a trigger, their immune system scrambles to defend itself by producing T cells, a type of white blood cell that helps ward off infections and other diseases. With psoriasis, however, T cell-production goes into overdrive, eventually causing inflammation and faster-than-usual growth of skin cells, leading to psoriasis symptoms.

The signs and symptoms of psoriasis vary depending on the type and severity of the skin disease. Some people may have one form of psoriasis, while others can have two or more.

Raised reddish patches. People with plaque psoriasis can experience a flare-up of red, raised patches. These patches can be itchy or painful or crack and bleed.

Scaly patches. Often seen in plaque psoriasis, scales are patches of built-up dead skin cells that have a silvery-white sheen. They often appear on top of raised, red patches that can be itchy or painful or crack and bleed. People with plaque psoriasis can experience a flare-up of symptoms on their scalp, knees, elbows, and lower back.

White pustules. A characteristic of pustular psoriasis, these white pus-filled blisters can cluster on the hands and feet or spread to most of the body. After the pustules appear, scaling usually follows. In people with von Zumbusch psoriasis, the pustules will dry after 24 to 48 hours, leaving the skin with a glazed appearance. In people with palmoplantar pustulosis, the pustules will turn brown, then peel, then start to crust.

Red, smooth lesions.Seen in inverse psoriasis, these very red lesions are smooth and shiny and are found in parts of the body with folds of skin, like the armpits, groin, and under the breasts. Because these lesions tend to be located in sensitive areas, they are prone to irritation from rubbing or sweating.

Red spots. A telltale sign of guttate psoriasis, these small, red spots are shaped like drops and usually appear on the torso, arms, and legs. In most cases, they arent as thick as plaque psoriasis lesions, but they can be widespread, numbering into the hundreds.

Nail changes.About 50% of people with psoriasis experience changes to their finger or toenails, including pitting (the appearance of holes in the nail), thickening, and discoloration, according to the NPF.

RELATED: 10 Things Your Nails Can Tell You About Your Health

Areas of the body normally affected by psoriasis

Back to top

There are no special diagnostic tests for psoriasis. Instead, a psoriasis diagnosis is made by a dermatologist, who will examine the skin lesions visually. In some cases, psoriasis can resemble other types of skin conditions, like eczema, so doctors may want to confirm the results with a biopsy. That involves removing some of the skin and looking at the sample under a microscope, where psoriasis tends to appear thicker than eczema.

Doctors may also take a detailed record of your familys medical history: About one-third of people with psoriasis have a first-degree relative who also has the condition. Health care providers may also try to pinpoint psoriasis triggers by asking whether their patients have been under stress lately or are taking a new medication.

Theres no one-size-fits-all psoriasis treatment, and the medications that work for some people may not work for others. The goal, however, is the same for everyone: to find psoriasis medications that can reduce or eliminate psoriasis symptoms. Here are some of the most commonly prescribed therapies.

Topical medications. A first-line form of therapy for mild to moderate conditions, topicals (in psoriasis cream, gel, and ointment forms) are applied directly to the skin in the hopes of reducing inflammation and slowing down skin cell growth. Some are available over-the-counter, like products with salicylic acid and coal tar as active ingredients, while others, like calcipotriene (a form of vitamin D3) and tazarotene (a vitamin A derivative known as a retinoid) are available by prescription. There are also special psoriasis shampoos that can help clear up scalp psoriasis; many contain coal tar and salicylic acid.

Phototherapy. Also called light therapy, phototherapy exposes a persons skin to ultraviolet light, which is thought to kill the immune cells contributing to psoriasis. Phototherapy can be administered in the form of UVB rays, a combination of UVA and UVB, or UVA rays alongside an oral or topical medication called psoralen (a treatment called PUVA). The catch: These treatments have to be done in a doctors office, a psoriasis clinic, or with a specialized phototherapy unit and usually require several visits, which can become expensive. Because indoor tanning increases the risk of skin cancer (especially melanoma), its not considered a safe substitute for phototherapy under medical supervision.

Systemic medications. If topical medications and phototherapy dont work, doctors may recommend taking systemics, or prescription drugs that affect the entire body. These meds can be taken orally or via an injection, and include cyclosporine (which suppresses immune system activity and slows skin cell growth), acitretin (an oral retinoid, or form of vitamin A, that slows down the speed at which skin cells grow and shed), and methotrexate (a medication that was originally used as a cancer treatment, but can also slow down the growth of skin cells).

Biologic drugs. Biologics contain human or animal proteins and can block certain immune cells that are involved in psoriasis. Theyre usually recommended for people with moderate to severe psoriasis and are administered via an injection or IV infusion. There are currently three types of biologics that can help treat psoriasis, all of which block immune system chemical messengers that promote inflammation called cytokines. The three types of biologics block the cytokines tumor necrosis factor alpha (TNF-alpha), interleukin 12, interleukin 23, and interleukin 17-A (IL-12, IL-23, and IL-17A, respectively).

RELATED: 21 Tips and Tricks for Treating Psoriasis

Alternative and complementary therapies. Some alternative therapiesincluding acupuncture, massage, and Reikimight help relieve certain psoriasis symptoms, like pain. They may also help control stress, a common psoriasis trigger. Other stress-relievers include meditation, mindfulness, exercise, yoga, and Tai Chi. Always talk to your doctor before beginning any alternative psoriasis treatments.

There is currently no cure for psoriasis. As a chronic autoimmune disease, most people with psoriasis will always have it. But it is possible to treat the condition. In fact, the right medications and therapies can reduce symptoms and even clear up the skin entirely in some people.

More psoriasis treatments may be available in the future. Researchers are currently trying to uncover what causes the lesions on a cellular level and how to prevent flare-ups caused by the immune system.

Back to top

For the millions of Americans who have psoriasis, the skin condition can pose many challenges. Not only can the pain and itching interfere with their ability to sleep or work, but research shows that many people with psoriasis feel unattractive; worse, if they feel self-conscious, they may withdraw from their friends and family and become isolated.

People with psoriasis are also twice as likely to be depressed as those who dont have the skin condition, according to the NPF, and they can also be more likely to have suicidal thoughts. If youre feeling a loss of energy, lack of interest in once-enjoyable activities, or an inability to focus, talk to your doctor about whether you may have depression or should see a mental health specialist.

An estimated 30% of people with psoriasis will also develop psoriatic arthritis, a disease which causes joint pain, stiffness, and swelling. Having psoriasis may also make people more likely to develop cardiovascular disease, obesity, and diabetes, according to the NPF.

RELATED: 12 Best and Worst Foods for Psoriasis

There are many ways that people living with psoriasis can manage the condition. This includes avoiding tobacco, alcohol, and unhealthy foods. Although there is no psoriasis diet, per se, eating healthy meals may help you feel better. You should also keep tabs on whether your joints feel stiff or sore or whether your nails are pitting or turning yellowtwo possible signs of psoriatic arthritis. Recognizing these symptomsand getting treatmentcan help prevent further damage to the joints.

Back to top

Anyone can develop psoriasiseven the most beautiful people on the planet. And as people who are paid to look flawless, many celebrities with psoriasis say that the skin condition delivers a serious blow to their self-esteem and fear that it can interfere with their careers.

In 2011, Kim Kardashian revealed her psoriasis diagnosis on an episode of Keeping Up With the Kardashians. Although her mother, Kris Jenner, was diagnosed with psoriasis at the age of 30, Kim was surprised to learn that she had the skin condition too. My career is doing ad campaigns and swimsuit photo shoots, she said in the episode. People dont understand the pressure on me to look perfect. Imagine what the tabloids would do to me if they saw all these spots.

Model and actress Cara Delevingne also has psoriasis, which she struggled to manage while runway modeling. She told Londons The Times in an interview that people would paint her body with foundation to cover up the patches. It was every single show, she said. People would put on gloves and not want to touch me.

Other models also struggle with psoriasis, like CariDee English, who won Americas Next Top Model in 2006. Partly in response to the hurtful tabloid headlines that called out the lesions on her legs, she posted before-and-after photos of one of her flare-ups, saying, I knew I didnt want anyone capturing my psoriasis in a way that wasnt empowering.

Other celebs who have psoriasis include golfer Phil Michelson, country singer LeAnn Rimes, and pop star Cyndi Lauper.

Back to top

Excerpt from:

Psoriasis – Causes, Symptoms and Treatment – Health.com

Psoriasis – Causes, Symptoms and Treatment – Health.com

Jump to: Types | Causes | Symptoms | Diagnosis | Treatment | Living with Psoriasis | Celebrities with Psoriasis

Psoriasis is a disease in which red, scaly patches form on the skin, typically on the elbows, knees, or scalp. An estimated 7.5 million people in the United States will develop the disease, most of them between the ages of 15 and 30. Many people with psoriasis experience pain, discomfort, and self-esteem problems that can interfere with their work and social life.

Although the exact cause of psoriasis is unknown, researchers say the disease is largely geneticits caused by a combination of genes that send the immune system into overdrive, triggering the rapid growth of skin cells that form patches and lesions.

A dermatologist can likely tell the difference between psoriasis and eczema, but to the untrained eye, these skin conditions can appear similar. Generally speaking, psoriasis appears as thick, red patches that have a scaly buildup on top, according to the American Academy of Dermatology (AAD). These lesions are usually well defined, whereas eczema tends to cause a rash and be accompanied by an intense itch.

In addition, psoriasis tends to occur on the outside of the knees and elbows, and on the lower back and scalp; eczema usually covers the elbow and knee creases and the neck or face.

Research published in 2015 in the Journal of Clinical Medicine suggested that infants and children with psoriasis may be particularly likely to be misdiagnosed with eczema because they may have less scaling than adults.

RELATED: Whats That Rash?

Back to top

Psoriasis can range in severity, from mild patches to severe lesions that can affect more than 5% of the skin. There are five types of the disease: plaque psoriasis, pustular psoriasis, guttate psoriasis, inverse psoriasis, and erythrodermic psoriasis. Some people will have one form, whereas others will have two or more.

Plaque psoriasis appears as red patches with silvery white scales, or buildup of dead skin cells, called plaques. Its the most common type of psoriasis, affecting up to 90% of all people with the disease, according to the AAD. Most often found on the scalp, elbows, lower back, and knees, the plaques themselves will be raised and have clear edges; they may also itch, crack, or bleed.

Pustular psoriasis is a form of psoriasis in which white pustules (or bumps filled with white pus) appear on the skin. In a typical cycle, the skin will turn red, break out in pustules, and then develop scales. There are three types of pustular psoriasis: von Zumbusch pustular psoriasis (which appears abruptly and can be accompanied with fever, chills, and dehydration), palmoplantar pustulosis (which appears on the soles of the feet and the hands), and acropustulosis (a rare form of psoriasis that forms on the ends of the fingers or toes).

Guttate psoriasis is a type of psoriasis that appears as red, scaly teardrop-shaped spots. (The word guttate is Latin for drop.) During a flare-up, hundreds of lesions can form on the arms, legs, and torso, although they can also appear on the face, ears, and scalp. Guttate is the second most common type of psoriasis, occurring in about 10% of all people with the disease. Its most likely to appear in people who are younger than 30, oftentimes after they develop an infection like strep throat.

Inverse psoriasis is a type of psoriasis that appears as smooth, bright red lesions in the armpit, groin, and other areas with folds of skin. Because these regions of the body are prone to sweating and rubbing, inverse psoriasis can be particularly irritating and hard to treat.

Erythrodermic psoriasis is rare but can require immediate treatment or even hospitalization. The lesions look like large sheets rather than small spots, as if the area has been burned, and tend to be severely itchy and painful. A flare-up can trigger swelling, infection, and increased heart rate.

Psoriasis is not contagiousits a genetic, autoimmune disease. Psoriasis lesions cannot infect other people; likewise, people cant catch psoriasis from someone else, whether through touching, sexual contact, or swimming in the same pool. Its unclear, however, whether a majority of the general public is aware of this fact. In a small 2015 survey in the Journal of the American Academy of Dermatology, about 60% of people said they thought that psoriasis was infectious, while 41% said they thought the lesions looked contagious.

RELATED: 14 Ways to Manage Your Psoriasis

Back to top

The simplest answer to the question of what causes psoriasis: your genetics. An estimated 10% of people inherit at least one of the genes that can cause psoriasis. (There are as many as 25 genetic mutations that make someone more likely to develop psoriasis.) But only 2% to 3% of people will develop the disease, according to the National Psoriasis Foundation (NSF). Therefore, researchers believe that psoriasis is caused by a certain combination of genes that spring into action after being exposed to a trigger. Common triggers include stress, an infection (like strep throat), and certain medications (like lithium). Cold, dry weather and sunburns may also trigger psoriasis flares.

When someone with psoriasis is exposed to a trigger, their immune system scrambles to defend itself by producing T cells, a type of white blood cell that helps ward off infections and other diseases. With psoriasis, however, T cell-production goes into overdrive, eventually causing inflammation and faster-than-usual growth of skin cells, leading to psoriasis symptoms.

The signs and symptoms of psoriasis vary depending on the type and severity of the skin disease. Some people may have one form of psoriasis, while others can have two or more.

Raised reddish patches. People with plaque psoriasis can experience a flare-up of red, raised patches. These patches can be itchy or painful or crack and bleed.

Scaly patches. Often seen in plaque psoriasis, scales are patches of built-up dead skin cells that have a silvery-white sheen. They often appear on top of raised, red patches that can be itchy or painful or crack and bleed. People with plaque psoriasis can experience a flare-up of symptoms on their scalp, knees, elbows, and lower back.

White pustules. A characteristic of pustular psoriasis, these white pus-filled blisters can cluster on the hands and feet or spread to most of the body. After the pustules appear, scaling usually follows. In people with von Zumbusch psoriasis, the pustules will dry after 24 to 48 hours, leaving the skin with a glazed appearance. In people with palmoplantar pustulosis, the pustules will turn brown, then peel, then start to crust.

Red, smooth lesions.Seen in inverse psoriasis, these very red lesions are smooth and shiny and are found in parts of the body with folds of skin, like the armpits, groin, and under the breasts. Because these lesions tend to be located in sensitive areas, they are prone to irritation from rubbing or sweating.

Red spots. A telltale sign of guttate psoriasis, these small, red spots are shaped like drops and usually appear on the torso, arms, and legs. In most cases, they arent as thick as plaque psoriasis lesions, but they can be widespread, numbering into the hundreds.

Nail changes.About 50% of people with psoriasis experience changes to their finger or toenails, including pitting (the appearance of holes in the nail), thickening, and discoloration, according to the NPF.

RELATED: 10 Things Your Nails Can Tell You About Your Health

Areas of the body normally affected by psoriasis

Back to top

There are no special diagnostic tests for psoriasis. Instead, a psoriasis diagnosis is made by a dermatologist, who will examine the skin lesions visually. In some cases, psoriasis can resemble other types of skin conditions, like eczema, so doctors may want to confirm the results with a biopsy. That involves removing some of the skin and looking at the sample under a microscope, where psoriasis tends to appear thicker than eczema.

Doctors may also take a detailed record of your familys medical history: About one-third of people with psoriasis have a first-degree relative who also has the condition. Health care providers may also try to pinpoint psoriasis triggers by asking whether their patients have been under stress lately or are taking a new medication.

Theres no one-size-fits-all psoriasis treatment, and the medications that work for some people may not work for others. The goal, however, is the same for everyone: to find psoriasis medications that can reduce or eliminate psoriasis symptoms. Here are some of the most commonly prescribed therapies.

Topical medications. A first-line form of therapy for mild to moderate conditions, topicals (in psoriasis cream, gel, and ointment forms) are applied directly to the skin in the hopes of reducing inflammation and slowing down skin cell growth. Some are available over-the-counter, like products with salicylic acid and coal tar as active ingredients, while others, like calcipotriene (a form of vitamin D3) and tazarotene (a vitamin A derivative known as a retinoid) are available by prescription. There are also special psoriasis shampoos that can help clear up scalp psoriasis; many contain coal tar and salicylic acid.

Phototherapy. Also called light therapy, phototherapy exposes a persons skin to ultraviolet light, which is thought to kill the immune cells contributing to psoriasis. Phototherapy can be administered in the form of UVB rays, a combination of UVA and UVB, or UVA rays alongside an oral or topical medication called psoralen (a treatment called PUVA). The catch: These treatments have to be done in a doctors office, a psoriasis clinic, or with a specialized phototherapy unit and usually require several visits, which can become expensive. Because indoor tanning increases the risk of skin cancer (especially melanoma), its not considered a safe substitute for phototherapy under medical supervision.

Systemic medications. If topical medications and phototherapy dont work, doctors may recommend taking systemics, or prescription drugs that affect the entire body. These meds can be taken orally or via an injection, and include cyclosporine (which suppresses immune system activity and slows skin cell growth), acitretin (an oral retinoid, or form of vitamin A, that slows down the speed at which skin cells grow and shed), and methotrexate (a medication that was originally used as a cancer treatment, but can also slow down the growth of skin cells).

Biologic drugs. Biologics contain human or animal proteins and can block certain immune cells that are involved in psoriasis. Theyre usually recommended for people with moderate to severe psoriasis and are administered via an injection or IV infusion. There are currently three types of biologics that can help treat psoriasis, all of which block immune system chemical messengers that promote inflammation called cytokines. The three types of biologics block the cytokines tumor necrosis factor alpha (TNF-alpha), interleukin 12, interleukin 23, and interleukin 17-A (IL-12, IL-23, and IL-17A, respectively).

RELATED: 21 Tips and Tricks for Treating Psoriasis

Alternative and complementary therapies. Some alternative therapiesincluding acupuncture, massage, and Reikimight help relieve certain psoriasis symptoms, like pain. They may also help control stress, a common psoriasis trigger. Other stress-relievers include meditation, mindfulness, exercise, yoga, and Tai Chi. Always talk to your doctor before beginning any alternative psoriasis treatments.

There is currently no cure for psoriasis. As a chronic autoimmune disease, most people with psoriasis will always have it. But it is possible to treat the condition. In fact, the right medications and therapies can reduce symptoms and even clear up the skin entirely in some people.

More psoriasis treatments may be available in the future. Researchers are currently trying to uncover what causes the lesions on a cellular level and how to prevent flare-ups caused by the immune system.

Back to top

For the millions of Americans who have psoriasis, the skin condition can pose many challenges. Not only can the pain and itching interfere with their ability to sleep or work, but research shows that many people with psoriasis feel unattractive; worse, if they feel self-conscious, they may withdraw from their friends and family and become isolated.

People with psoriasis are also twice as likely to be depressed as those who dont have the skin condition, according to the NPF, and they can also be more likely to have suicidal thoughts. If youre feeling a loss of energy, lack of interest in once-enjoyable activities, or an inability to focus, talk to your doctor about whether you may have depression or should see a mental health specialist.

An estimated 30% of people with psoriasis will also develop psoriatic arthritis, a disease which causes joint pain, stiffness, and swelling. Having psoriasis may also make people more likely to develop cardiovascular disease, obesity, and diabetes, according to the NPF.

RELATED: 12 Best and Worst Foods for Psoriasis

There are many ways that people living with psoriasis can manage the condition. This includes avoiding tobacco, alcohol, and unhealthy foods. Although there is no psoriasis diet, per se, eating healthy meals may help you feel better. You should also keep tabs on whether your joints feel stiff or sore or whether your nails are pitting or turning yellowtwo possible signs of psoriatic arthritis. Recognizing these symptomsand getting treatmentcan help prevent further damage to the joints.

Back to top

Anyone can develop psoriasiseven the most beautiful people on the planet. And as people who are paid to look flawless, many celebrities with psoriasis say that the skin condition delivers a serious blow to their self-esteem and fear that it can interfere with their careers.

In 2011, Kim Kardashian revealed her psoriasis diagnosis on an episode of Keeping Up With the Kardashians. Although her mother, Kris Jenner, was diagnosed with psoriasis at the age of 30, Kim was surprised to learn that she had the skin condition too. My career is doing ad campaigns and swimsuit photo shoots, she said in the episode. People dont understand the pressure on me to look perfect. Imagine what the tabloids would do to me if they saw all these spots.

Model and actress Cara Delevingne also has psoriasis, which she struggled to manage while runway modeling. She told Londons The Times in an interview that people would paint her body with foundation to cover up the patches. It was every single show, she said. People would put on gloves and not want to touch me.

Other models also struggle with psoriasis, like CariDee English, who won Americas Next Top Model in 2006. Partly in response to the hurtful tabloid headlines that called out the lesions on her legs, she posted before-and-after photos of one of her flare-ups, saying, I knew I didnt want anyone capturing my psoriasis in a way that wasnt empowering.

Other celebs who have psoriasis include golfer Phil Michelson, country singer LeAnn Rimes, and pop star Cyndi Lauper.

Back to top

Go here to read the rest:

Psoriasis – Causes, Symptoms and Treatment – Health.com

Psoriasis | Psoriatic Arthritis | MedlinePlus

Psoriasis is a skin disease that causes itchy or sore patches of thick, red skin with silvery scales. You usually get the patches on your elbows, knees, scalp, back, face, palms and feet, but they can show up on other parts of your body. Some people who have psoriasis also get a form of arthritis called psoriatic arthritis.

A problem with your immune system causes psoriasis. In a process called cell turnover, skin cells that grow deep in your skin rise to the surface. Normally, this takes a month. In psoriasis, it happens in just days because your cells rise too fast.

Psoriasis can be hard to diagnose because it can look like other skin diseases. Your doctor might need to look at a small skin sample under a microscope.

Psoriasis can last a long time, even a lifetime. Symptoms come and go. Things that make them worse include

Psoriasis usually occurs in adults. It sometimes runs in families. Treatments include creams, medicines, and light therapy.

NIH: National Institute of Arthritis and Musculoskeletal and Skin Diseases

See the article here:

Psoriasis | Psoriatic Arthritis | MedlinePlus

GEN

3D Microscopy of Immune Cell Migration in Zebrafish Ear

Nobel-prize-winning physicist Eric Betzig, Ph.D., recently lead a team to develop a revolutionary way of imaging live cells. As reported in Science , the Howard Hughes Medical Institute team …

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GEN

Psoriasis – Causes, Symptoms and Treatment – Health.com …

Jump to: Types | Causes | Symptoms | Diagnosis | Treatment | Living with Psoriasis | Celebrities with Psoriasis

Psoriasis is a disease in which red, scaly patches form on the skin, typically on the elbows, knees, or scalp. An estimated 7.5 million people in the United States will develop the disease, most of them between the ages of 15 and 30. Many people with psoriasis experience pain, discomfort, and self-esteem problems that can interfere with their work and social life.

Although the exact cause of psoriasis is unknown, researchers say the disease is largely geneticits caused by a combination of genes that send the immune system into overdrive, triggering the rapid growth of skin cells that form patches and lesions.

A dermatologist can likely tell the difference between psoriasis and eczema, but to the untrained eye, these skin conditions can appear similar. Generally speaking, psoriasis appears as thick, red patches that have a scaly buildup on top, according to the American Academy of Dermatology (AAD). These lesions are usually well defined, whereas eczema tends to cause a rash and be accompanied by an intense itch.

In addition, psoriasis tends to occur on the outside of the knees and elbows, and on the lower back and scalp; eczema usually covers the elbow and knee creases and the neck or face.

Research published in 2015 in the Journal of Clinical Medicine suggested that infants and children with psoriasis may be particularly likely to be misdiagnosed with eczema because they may have less scaling than adults.

RELATED: Whats That Rash?

Back to top

Psoriasis can range in severity, from mild patches to severe lesions that can affect more than 5% of the skin. There are five types of the disease: plaque psoriasis, pustular psoriasis, guttate psoriasis, inverse psoriasis, and erythrodermic psoriasis. Some people will have one form, whereas others will have two or more.

Plaque psoriasis appears as red patches with silvery white scales, or buildup of dead skin cells, called plaques. Its the most common type of psoriasis, affecting up to 90% of all people with the disease, according to the AAD. Most often found on the scalp, elbows, lower back, and knees, the plaques themselves will be raised and have clear edges; they may also itch, crack, or bleed.

Pustular psoriasis is a form of psoriasis in which white pustules (or bumps filled with white pus) appear on the skin. In a typical cycle, the skin will turn red, break out in pustules, and then develop scales. There are three types of pustular psoriasis: von Zumbusch pustular psoriasis (which appears abruptly and can be accompanied with fever, chills, and dehydration), palmoplantar pustulosis (which appears on the soles of the feet and the hands), and acropustulosis (a rare form of psoriasis that forms on the ends of the fingers or toes).

Guttate psoriasis is a type of psoriasis that appears as red, scaly teardrop-shaped spots. (The word guttate is Latin for drop.) During a flare-up, hundreds of lesions can form on the arms, legs, and torso, although they can also appear on the face, ears, and scalp. Guttate is the second most common type of psoriasis, occurring in about 10% of all people with the disease. Its most likely to appear in people who are younger than 30, oftentimes after they develop an infection like strep throat.

Inverse psoriasis is a type of psoriasis that appears as smooth, bright red lesions in the armpit, groin, and other areas with folds of skin. Because these regions of the body are prone to sweating and rubbing, inverse psoriasis can be particularly irritating and hard to treat.

Erythrodermic psoriasis is rare but can require immediate treatment or even hospitalization. The lesions look like large sheets rather than small spots, as if the area has been burned, and tend to be severely itchy and painful. A flare-up can trigger swelling, infection, and increased heart rate.

Psoriasis is not contagiousits a genetic, autoimmune disease. Psoriasis lesions cannot infect other people; likewise, people cant catch psoriasis from someone else, whether through touching, sexual contact, or swimming in the same pool. Its unclear, however, whether a majority of the general public is aware of this fact. In a small 2015 survey in the Journal of the American Academy of Dermatology, about 60% of people said they thought that psoriasis was infectious, while 41% said they thought the lesions looked contagious.

RELATED: 14 Ways to Manage Your Psoriasis

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The simplest answer to the question of what causes psoriasis: your genetics. An estimated 10% of people inherit at least one of the genes that can cause psoriasis. (There are as many as 25 genetic mutations that make someone more likely to develop psoriasis.) But only 2% to 3% of people will develop the disease, according to the National Psoriasis Foundation (NSF). Therefore, researchers believe that psoriasis is caused by a certain combination of genes that spring into action after being exposed to a trigger. Common triggers include stress, an infection (like strep throat), and certain medications (like lithium). Cold, dry weather and sunburns may also trigger psoriasis flares.

When someone with psoriasis is exposed to a trigger, their immune system scrambles to defend itself by producing T cells, a type of white blood cell that helps ward off infections and other diseases. With psoriasis, however, T cell-production goes into overdrive, eventually causing inflammation and faster-than-usual growth of skin cells, leading to psoriasis symptoms.

The signs and symptoms of psoriasis vary depending on the type and severity of the skin disease. Some people may have one form of psoriasis, while others can have two or more.

Raised reddish patches. People with plaque psoriasis can experience a flare-up of red, raised patches. These patches can be itchy or painful or crack and bleed.

Scaly patches. Often seen in plaque psoriasis, scales are patches of built-up dead skin cells that have a silvery-white sheen. They often appear on top of raised, red patches that can be itchy or painful or crack and bleed. People with plaque psoriasis can experience a flare-up of symptoms on their scalp, knees, elbows, and lower back.

White pustules. A characteristic of pustular psoriasis, these white pus-filled blisters can cluster on the hands and feet or spread to most of the body. After the pustules appear, scaling usually follows. In people with von Zumbusch psoriasis, the pustules will dry after 24 to 48 hours, leaving the skin with a glazed appearance. In people with palmoplantar pustulosis, the pustules will turn brown, then peel, then start to crust.

Red, smooth lesions.Seen in inverse psoriasis, these very red lesions are smooth and shiny and are found in parts of the body with folds of skin, like the armpits, groin, and under the breasts. Because these lesions tend to be located in sensitive areas, they are prone to irritation from rubbing or sweating.

Red spots. A telltale sign of guttate psoriasis, these small, red spots are shaped like drops and usually appear on the torso, arms, and legs. In most cases, they arent as thick as plaque psoriasis lesions, but they can be widespread, numbering into the hundreds.

Nail changes.About 50% of people with psoriasis experience changes to their finger or toenails, including pitting (the appearance of holes in the nail), thickening, and discoloration, according to the NPF.

RELATED: 10 Things Your Nails Can Tell You About Your Health

Areas of the body normally affected by psoriasis

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There are no special diagnostic tests for psoriasis. Instead, a psoriasis diagnosis is made by a dermatologist, who will examine the skin lesions visually. In some cases, psoriasis can resemble other types of skin conditions, like eczema, so doctors may want to confirm the results with a biopsy. That involves removing some of the skin and looking at the sample under a microscope, where psoriasis tends to appear thicker than eczema.

Doctors may also take a detailed record of your familys medical history: About one-third of people with psoriasis have a first-degree relative who also has the condition. Health care providers may also try to pinpoint psoriasis triggers by asking whether their patients have been under stress lately or are taking a new medication.

Theres no one-size-fits-all psoriasis treatment, and the medications that work for some people may not work for others. The goal, however, is the same for everyone: to find psoriasis medications that can reduce or eliminate psoriasis symptoms. Here are some of the most commonly prescribed therapies.

Topical medications. A first-line form of therapy for mild to moderate conditions, topicals (in psoriasis cream, gel, and ointment forms) are applied directly to the skin in the hopes of reducing inflammation and slowing down skin cell growth. Some are available over-the-counter, like products with salicylic acid and coal tar as active ingredients, while others, like calcipotriene (a form of vitamin D3) and tazarotene (a vitamin A derivative known as a retinoid) are available by prescription. There are also special psoriasis shampoos that can help clear up scalp psoriasis; many contain coal tar and salicylic acid.

Phototherapy. Also called light therapy, phototherapy exposes a persons skin to ultraviolet light, which is thought to kill the immune cells contributing to psoriasis. Phototherapy can be administered in the form of UVB rays, a combination of UVA and UVB, or UVA rays alongside an oral or topical medication called psoralen (a treatment called PUVA). The catch: These treatments have to be done in a doctors office, a psoriasis clinic, or with a specialized phototherapy unit and usually require several visits, which can become expensive. Because indoor tanning increases the risk of skin cancer (especially melanoma), its not considered a safe substitute for phototherapy under medical supervision.

Systemic medications. If topical medications and phototherapy dont work, doctors may recommend taking systemics, or prescription drugs that affect the entire body. These meds can be taken orally or via an injection, and include cyclosporine (which suppresses immune system activity and slows skin cell growth), acitretin (an oral retinoid, or form of vitamin A, that slows down the speed at which skin cells grow and shed), and methotrexate (a medication that was originally used as a cancer treatment, but can also slow down the growth of skin cells).

Biologic drugs. Biologics contain human or animal proteins and can block certain immune cells that are involved in psoriasis. Theyre usually recommended for people with moderate to severe psoriasis and are administered via an injection or IV infusion. There are currently three types of biologics that can help treat psoriasis, all of which block immune system chemical messengers that promote inflammation called cytokines. The three types of biologics block the cytokines tumor necrosis factor alpha (TNF-alpha), interleukin 12, interleukin 23, and interleukin 17-A (IL-12, IL-23, and IL-17A, respectively).

RELATED: 21 Tips and Tricks for Treating Psoriasis

Alternative and complementary therapies. Some alternative therapiesincluding acupuncture, massage, and Reikimight help relieve certain psoriasis symptoms, like pain. They may also help control stress, a common psoriasis trigger. Other stress-relievers include meditation, mindfulness, exercise, yoga, and Tai Chi. Always talk to your doctor before beginning any alternative psoriasis treatments.

There is currently no cure for psoriasis. As a chronic autoimmune disease, most people with psoriasis will always have it. But it is possible to treat the condition. In fact, the right medications and therapies can reduce symptoms and even clear up the skin entirely in some people.

More psoriasis treatments may be available in the future. Researchers are currently trying to uncover what causes the lesions on a cellular level and how to prevent flare-ups caused by the immune system.

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For the millions of Americans who have psoriasis, the skin condition can pose many challenges. Not only can the pain and itching interfere with their ability to sleep or work, but research shows that many people with psoriasis feel unattractive; worse, if they feel self-conscious, they may withdraw from their friends and family and become isolated.

People with psoriasis are also twice as likely to be depressed as those who dont have the skin condition, according to the NPF, and they can also be more likely to have suicidal thoughts. If youre feeling a loss of energy, lack of interest in once-enjoyable activities, or an inability to focus, talk to your doctor about whether you may have depression or should see a mental health specialist.

An estimated 30% of people with psoriasis will also develop psoriatic arthritis, a disease which causes joint pain, stiffness, and swelling. Having psoriasis may also make people more likely to develop cardiovascular disease, obesity, and diabetes, according to the NPF.

RELATED: 12 Best and Worst Foods for Psoriasis

There are many ways that people living with psoriasis can manage the condition. This includes avoiding tobacco, alcohol, and unhealthy foods. Although there is no psoriasis diet, per se, eating healthy meals may help you feel better. You should also keep tabs on whether your joints feel stiff or sore or whether your nails are pitting or turning yellowtwo possible signs of psoriatic arthritis. Recognizing these symptomsand getting treatmentcan help prevent further damage to the joints.

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Anyone can develop psoriasiseven the most beautiful people on the planet. And as people who are paid to look flawless, many celebrities with psoriasis say that the skin condition delivers a serious blow to their self-esteem and fear that it can interfere with their careers.

In 2011, Kim Kardashian revealed her psoriasis diagnosis on an episode of Keeping Up With the Kardashians. Although her mother, Kris Jenner, was diagnosed with psoriasis at the age of 30, Kim was surprised to learn that she had the skin condition too. My career is doing ad campaigns and swimsuit photo shoots, she said in the episode. People dont understand the pressure on me to look perfect. Imagine what the tabloids would do to me if they saw all these spots.

Model and actress Cara Delevingne also has psoriasis, which she struggled to manage while runway modeling. She told Londons The Times in an interview that people would paint her body with foundation to cover up the patches. It was every single show, she said. People would put on gloves and not want to touch me.

Other models also struggle with psoriasis, like CariDee English, who won Americas Next Top Model in 2006. Partly in response to the hurtful tabloid headlines that called out the lesions on her legs, she posted before-and-after photos of one of her flare-ups, saying, I knew I didnt want anyone capturing my psoriasis in a way that wasnt empowering.

Other celebs who have psoriasis include golfer Phil Michelson, country singer LeAnn Rimes, and pop star Cyndi Lauper.

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Psoriasis – Causes, Symptoms and Treatment – Health.com …

Human genetics | biology | Britannica.com

Human genetics, study of the inheritance of characteristics by children from parents. Inheritance in humans does not differ in any fundamental way from that in other organisms.

The study of human heredity occupies a central position in genetics. Much of this interest stems from a basic desire to know who humans are and why they are as they are. At a more practical level, an understanding of human heredity is of critical importance in the prediction, diagnosis, and treatment of diseases that have a genetic component. The quest to determine the genetic basis of human health has given rise to the field of medical genetics. In general, medicine has given focus and purpose to human genetics, so the terms medical genetics and human genetics are often considered synonymous.

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genetics: Human genetics

Some geneticists specialize in the hereditary processes of human genetics. Most of the emphasis is on understanding and treating genetic disease and genetically influenced ill health, areas collectively known as medical genetics. One broad area of activity is laboratory research dealing with the

A new era in cytogenetics, the field of investigation concerned with studies of the chromosomes, began in 1956 with the discovery by Jo Hin Tjio and Albert Levan that human somatic cells contain 23 pairs of chromosomes. Since that time the field has advanced with amazing rapidity and has demonstrated that human chromosome aberrations rank as major causes of fetal death and of tragic human diseases, many of which are accompanied by mental retardation. Since the chromosomes can be delineated only during mitosis, it is necessary to examine material in which there are many dividing cells. This can usually be accomplished by culturing cells from the blood or skin, since only the bone marrow cells (not readily sampled except during serious bone marrow disease such as leukemia) have sufficient mitoses in the absence of artificial culture. After growth, the cells are fixed on slides and then stained with a variety of DNA-specific stains that permit the delineation and identification of the chromosomes. The Denver system of chromosome classification, established in 1959, identified the chromosomes by their length and the position of the centromeres. Since then the method has been improved by the use of special staining techniques that impart unique light and dark bands to each chromosome. These bands permit the identification of chromosomal regions that are duplicated, missing, or transposed to other chromosomes.

Micrographs showing the karyotypes (i.e., the physical appearance of the chromosome) of a male and a female have been produced. In a typical micrograph the 46 human chromosomes (the diploid number) are arranged in homologous pairs, each consisting of one maternally derived and one paternally derived member. The chromosomes are all numbered except for the X and the Y chromosomes, which are the sex chromosomes. In humans, as in all mammals, the normal female has two X chromosomes and the normal male has one X chromosome and one Y chromosome. The female is thus the homogametic sex, as all her gametes normally have one X chromosome. The male is heterogametic, as he produces two types of gametesone type containing an X chromosome and the other containing a Y chromosome. There is good evidence that the Y chromosome in humans, unlike that in Drosophila, is necessary (but not sufficient) for maleness.

A human individual arises through the union of two cells, an egg from the mother and a sperm from the father. Human egg cells are barely visible to the naked eye. They are shed, usually one at a time, from the ovary into the oviducts (fallopian tubes), through which they pass into the uterus. Fertilization, the penetration of an egg by a sperm, occurs in the oviducts. This is the main event of sexual reproduction and determines the genetic constitution of the new individual.

Human sex determination is a genetic process that depends basically on the presence of the Y chromosome in the fertilized egg. This chromosome stimulates a change in the undifferentiated gonad into that of the male (a testicle). The gonadal action of the Y chromosome is mediated by a gene located near the centromere; this gene codes for the production of a cell surface molecule called the H-Y antigen. Further development of the anatomic structures, both internal and external, that are associated with maleness is controlled by hormones produced by the testicle. The sex of an individual can be thought of in three different contexts: chromosomal sex, gonadal sex, and anatomic sex. Discrepancies between these, especially the latter two, result in the development of individuals with ambiguous sex, often called hermaphrodites. The phenomenon of homosexuality is of uncertain cause and is unrelated to the above sex-determining factors. It is of interest that in the absence of a male gonad (testicle) the internal and external sex anatomy is always female, even in the absence of a female ovary. A female without ovaries will, of course, be infertile and will not experience any of the female developmental changes normally associated with puberty. Such a female will often have Turners syndrome.

If X-containing and Y-containing sperm are produced in equal numbers, then according to simple chance one would expect the sex ratio at conception (fertilization) to be half boys and half girls, or 1 : 1. Direct observation of sex ratios among newly fertilized human eggs is not yet feasible, and sex-ratio data are usually collected at the time of birth. In almost all human populations of newborns, there is a slight excess of males; about 106 boys are born for every100 girls. Throughout life, however, there is a slightly greater mortality of males; this slowly alters the sex ratio until, beyond the age of about 50 years, there is an excess of females. Studies indicate that male embryos suffer a relatively greater degree of prenatal mortality, so the sex ratio at conception might be expected to favour males even more than the 106 : 100 ratio observed at birth would suggest. Firm explanations for the apparent excess of male conceptions have not been established; it is possible that Y-containing sperm survive better within the female reproductive tract, or they may be a little more successful in reaching the egg in order to fertilize it. In any case, the sex differences are small, the statistical expectation for a boy (or girl) at any single birth still being close to one out of two.

During gestationthe period of nine months between fertilization and the birth of the infanta remarkable series of developmental changes occur. Through the process of mitosis, the total number of cells changes from 1 (the fertilized egg) to about 2 1011. In addition, these cells differentiate into hundreds of different types with specific functions (liver cells, nerve cells, muscle cells, etc.). A multitude of regulatory processes, both genetically and environmentally controlled, accomplish this differentiation. Elucidation of the exquisite timing of these processes remains one of the great challenges of human biology.

Immunity is the ability of an individual to recognize the self molecules that make up ones own body and to distinguish them from such nonself molecules as those found in infectious microorganisms and toxins. This process has a prominent genetic component. Knowledge of the genetic and molecular basis of the mammalian immune system has increased in parallel with the explosive advances made in somatic cell and molecular genetics.

There are two major components of the immune system, both originating from the same precursor stem cells. The bursa component provides B lymphocytes, a class of white blood cells that, when appropriately stimulated, differentiate into plasma cells. These latter cells produce circulating soluble proteins called antibodies or immunoglobulins. Antibodies are produced in response to substances called antigens, most of which are foreign proteins or polysaccharides. An antibody molecule can recognize a specific antigen, combine with it, and initiate its destruction. This so-called humoral immunity is accomplished through a complicated series of interactions with other molecules and cells; some of these interactions are mediated by another group of lymphocytes, the T lymphocytes, which are derived from the thymus gland. Once a B lymphocyte has been exposed to a specific antigen, it remembers the contact so that future exposure will cause an accelerated and magnified immune reaction. This is a manifestation of what has been called immunological memory.

The thymus component of the immune system centres on the thymus-derived T lymphocytes. In addition to regulating the B cells in producing humoral immunity, the T cells also directly attack cells that display foreign antigens. This process, called cellular immunity, is of great importance in protecting the body against a variety of viruses as well as cancer cells. Cellular immunity is also the chief cause of the rejection of organ transplants. The T lymphocytes provide a complex network consisting of a series of helper cells (which are antigen-specific), amplifier cells, suppressor cells, and cytotoxic (killer) cells, all of which are important in immune regulation.

One of the central problems in understanding the genetics of the immune system has been in explaining the genetic regulation of antibody production. Immunobiologists have demonstrated that the system can produce well over one million specific antibodies, each corresponding to a particular antigen. It would be difficult to envisage that each antibody is encoded by a separate gene; such an arrangement would require a disproportionate share of the entire human genome. Recombinant DNA analysis has illuminated the mechanisms by which a limited number of immunoglobulin genes can encode this vast number of antibodies.

Each antibody molecule consists of several different polypeptide chainsthe light chains (L) and the longer heavy chains (H). The latter determine to which of five different classes (IgM, IgG, IgA, IgD, or IgE) an immunoglobulin belongs. Both the L and H chains are unique among proteins in that they contain constant and variable parts. The constant parts have relatively identical amino acid sequences in any given antibody. The variable parts, on the other hand, have different amino acid sequences in each antibody molecule. It is the variable parts, then, that determine the specificity of the antibody.

Recombinant DNA studies of immunoglobulin genes in mice have revealed that the light-chain genes are encoded in four separate parts in germ-line DNA: a leader segment (L), a variable segment (V), a joining segment (J), and a constant segment (C). These segments are widely separated in the DNA of an embryonic cell, but in a mature B lymphocyte they are found in relative proximity (albeit separated by introns). The mouse has more than 200 light-chain variable region genes, only one of which will be incorporated into the proximal sequence that codes for the antibody production in a given B lymphocyte. Antibody diversity is greatly enhanced by this system, as the V and J segments rearrange and assort randomly in each B-lymphocyte precursor cell. The mechanisms by which this DNA rearrangement takes place are not clear, but transposons are undoubtedly involved. Similar combinatorial processes take place in the genes that code for the heavy chains; furthermore, both the light-chain and heavy-chain genes can undergo somatic mutations to create new antibody-coding sequences. The net effect of these combinatorial and mutational processes enables the coding of millions of specific antibody molecules from a limited number of genes. It should be stressed, however, that each B lymphocyte can produce only one antibody. It is the B lymphocyte population as a whole that produces the tremendous variety of antibodies in humans and other mammals.

Plasma cell tumours (myelomas) have made it possible to study individual antibodies, since these tumours, which are descendants of a single plasma cell, produce one antibody in abundance. Another method of obtaining large amounts of a specific antibody is by fusing a B lymphocyte with a rapidly growing cancer cell. The resultant hybrid cell, known as a hybridoma, multiplies rapidly in culture. Since the antibodies obtained from hybridomas are produced by clones derived from a single lymphocyte, they are called monoclonal antibodies.

As has been stated, cellular immunity is mediated by T lymphocytes that can recognize infected body cells, cancer cells, and the cells of a foreign transplant. The control of cellular immune reactions is provided by a linked group of genes, known as the major histocompatibility complex (MHC). These genes code for the major histocompatibility antigens, which are found on the surface of almost all nucleated somatic cells. The major histocompatibility antigens were first discovered on the leukocytes (white blood cells) and are therefore usually referred to as the HLA (human leukocyte group A) antigens.

The advent of the transplantation of human organs in the 1950s made the question of tissue compatibility between donor and recipient of vital importance, and it was in this context that the HLA antigens and the MHC were elucidated. Investigators found that the MHC resides on the short arm of chromosome 6, on four closely associated sites designated HLA-A, HLA-B, HLA-C, and HLA-D. Each locus is highly polymorphic; i.e., each is represented by a great many alleles within the human gene pool. These alleles, like those of the ABO blood group system, are expressed in codominant fashion. Because of the large number of alleles at each HLA locus, there is an extremely low probability of any two individuals (other than siblings) having identical HLA genotypes. (Since a person inherits one chromosome 6 from each parent, siblings have a 25 percent probability of having received the same paternal and maternal chromosomes 6 and thus of being HLA matched.)

Although HLA antigens are largely responsible for the rejection of organ transplants, it is obvious that the MHC did not evolve to prevent the transfer of organs from one person to another. Indeed, information obtained from the histocompatibility complex in the mouse (which is very similar in its genetic organization to that of the human) suggests that a primary function of the HLA antigens is to regulate the number of specific cytotoxic T killer cells, which have the ability to destroy virus-infected cells and cancer cells.

More is known about the genetics of the blood than about any other human tissue. One reason for this is that blood samples can be easily secured and subjected to biochemical analysis without harm or major discomfort to the person being tested. Perhaps a more cogent reason is that many chemical properties of human blood display relatively simple patterns of inheritance.

Certain chemical substances within the red blood cells (such as the ABO and MN substances noted above) may serve as antigens. When cells that contain specific antigens are introduced into the body of an experimental animal such as a rabbit, the animal responds by producing antibodies in its own blood.

In addition to the ABO and MN systems, geneticists have identified about 14 blood-type gene systems associated with other chromosomal locations. The best known of these is the Rh system. The Rh antigens are of particular importance in human medicine. Curiously, however, their existence was discovered in monkeys. When blood from the rhesus monkey (hence the designation Rh) is injected into rabbits, the rabbits produce so-called Rh antibodies that will agglutinate not only the red blood cells of the monkey but the cells of a large proportion of human beings as well. Some people (Rh-negative individuals), however, lack the Rh antigen; the proportion of such persons varies from one human population to another. Akin to data concerning the ABO system, the evidence for Rh genes indicates that only a single chromosome locus (called r) is involved and is located on chromosome 1. At least 35 Rh alleles are known for the r location; basically the Rh-negative condition is recessive.

A medical problem may arise when a woman who is Rh-negative carries a fetus that is Rh-positive. The first such child may have no difficulty, but later similar pregnancies may produce severely anemic newborn infants. Exposure to the red blood cells of the first Rh-positive fetus appears to immunize the Rh-negative mother, that is, she develops antibodies that may produce permanent (sometimes fatal) brain damage in any subsequent Rh-positive fetus. Damage arises from the scarcity of oxygen reaching the fetal brain because of the severe destruction of red blood cells. Measures are available for avoiding the severe effects of Rh incompatibility by transfusions to the fetus within the uterus; however, genetic counselling before conception is helpful so that the mother can receive Rh immunoglobulin immediately after her first and any subsequent pregnancies involving an Rh-positive fetus. This immunoglobulin effectively destroys the fetal red blood cells before the mothers immune system is stimulated. The mother thus avoids becoming actively immunized against the Rh antigen and will not produce antibodies that could attack the red blood cells of a future Rh-positive fetus.

Human serum, the fluid portion of the blood that remains after clotting, contains various proteins that have been shown to be under genetic control. Study of genetic influences has flourished since the development of precise methods for separating and identifying serum proteins. These move at different rates under the impetus of an electrical field (electrophoresis), as do proteins from many other sources (e.g., muscle or nerve). Since the composition of a protein is specified by the structure of its corresponding gene, biochemical studies based on electrophoresis permit direct study of tissue substances that are only a metabolic step or two away from the genes themselves.

Electrophoretic studies have revealed that at least one-third of the human serum proteins occur in variant forms. Many of the serum proteins are polymorphic, occurring as two or more variants with a frequency of not less than 1 percent each in a population. Patterns of polymorphic serum protein variants have been used to determine whether twins are identical (as in assessing compatibility for organ transplants) or whether two individuals are related (as in resolving paternity suits). Whether the different forms have a selective advantage is not generally known.

Much attention in the genetics of substances in the blood has been centred on serum proteins called haptoglobins, transferrins (which transport iron), and gamma globulins (a number of which are known to immunize against infectious diseases). Haptoglobins appear to relate to two common alleles at a single chromosome locus; the mode of inheritance of the other two seems more complicated, about 18 kinds of transferrins having been described. Like blood-cell antigen genes, serum-protein genes are distributed worldwide in the human population in a way that permits their use in tracing the origin and migration of different groups of people.

Hundreds of variants of hemoglobin have been identified by electrophoresis, but relatively few are frequent enough to be called polymorphisms. Of the polymorphisms, the alleles for sickle-cell and thalassemia hemoglobins produce serious disease in homozygotes, whereas others (hemoglobins C, D, and E) do not. The sickle-cell polymorphism confers a selective advantage on the heterozygote living in a malarial environment; the thalassemia polymorphism provides a similar advantage.

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Human genetics | biology | Britannica.com

Psoriasis – Causes, Symptoms and Treatment – Health.com …

Jump to: Types | Causes | Symptoms | Diagnosis | Treatment | Living with Psoriasis | Celebrities with Psoriasis

Psoriasis is a disease in which red, scaly patches form on the skin, typically on the elbows, knees, or scalp. An estimated 7.5 million people in the United States will develop the disease, most of them between the ages of 15 and 30. Many people with psoriasis experience pain, discomfort, and self-esteem problems that can interfere with their work and social life.

Although the exact cause of psoriasis is unknown, researchers say the disease is largely geneticits caused by a combination of genes that send the immune system into overdrive, triggering the rapid growth of skin cells that form patches and lesions.

A dermatologist can likely tell the difference between psoriasis and eczema, but to the untrained eye, these skin conditions can appear similar. Generally speaking, psoriasis appears as thick, red patches that have a scaly buildup on top, according to the American Academy of Dermatology (AAD). These lesions are usually well defined, whereas eczema tends to cause a rash and be accompanied by an intense itch.

In addition, psoriasis tends to occur on the outside of the knees and elbows, and on the lower back and scalp; eczema usually covers the elbow and knee creases and the neck or face.

Research published in 2015 in the Journal of Clinical Medicine suggested that infants and children with psoriasis may be particularly likely to be misdiagnosed with eczema because they may have less scaling than adults.

RELATED: Whats That Rash?

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Psoriasis can range in severity, from mild patches to severe lesions that can affect more than 5% of the skin. There are five types of the disease: plaque psoriasis, pustular psoriasis, guttate psoriasis, inverse psoriasis, and erythrodermic psoriasis. Some people will have one form, whereas others will have two or more.

Plaque psoriasis appears as red patches with silvery white scales, or buildup of dead skin cells, called plaques. Its the most common type of psoriasis, affecting up to 90% of all people with the disease, according to the AAD. Most often found on the scalp, elbows, lower back, and knees, the plaques themselves will be raised and have clear edges; they may also itch, crack, or bleed.

Pustular psoriasis is a form of psoriasis in which white pustules (or bumps filled with white pus) appear on the skin. In a typical cycle, the skin will turn red, break out in pustules, and then develop scales. There are three types of pustular psoriasis: von Zumbusch pustular psoriasis (which appears abruptly and can be accompanied with fever, chills, and dehydration), palmoplantar pustulosis (which appears on the soles of the feet and the hands), and acropustulosis (a rare form of psoriasis that forms on the ends of the fingers or toes).

Guttate psoriasis is a type of psoriasis that appears as red, scaly teardrop-shaped spots. (The word guttate is Latin for drop.) During a flare-up, hundreds of lesions can form on the arms, legs, and torso, although they can also appear on the face, ears, and scalp. Guttate is the second most common type of psoriasis, occurring in about 10% of all people with the disease. Its most likely to appear in people who are younger than 30, oftentimes after they develop an infection like strep throat.

Inverse psoriasis is a type of psoriasis that appears as smooth, bright red lesions in the armpit, groin, and other areas with folds of skin. Because these regions of the body are prone to sweating and rubbing, inverse psoriasis can be particularly irritating and hard to treat.

Erythrodermic psoriasis is rare but can require immediate treatment or even hospitalization. The lesions look like large sheets rather than small spots, as if the area has been burned, and tend to be severely itchy and painful. A flare-up can trigger swelling, infection, and increased heart rate.

Psoriasis is not contagiousits a genetic, autoimmune disease. Psoriasis lesions cannot infect other people; likewise, people cant catch psoriasis from someone else, whether through touching, sexual contact, or swimming in the same pool. Its unclear, however, whether a majority of the general public is aware of this fact. In a small 2015 survey in the Journal of the American Academy of Dermatology, about 60% of people said they thought that psoriasis was infectious, while 41% said they thought the lesions looked contagious.

RELATED: 14 Ways to Manage Your Psoriasis

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The simplest answer to the question of what causes psoriasis: your genetics. An estimated 10% of people inherit at least one of the genes that can cause psoriasis. (There are as many as 25 genetic mutations that make someone more likely to develop psoriasis.) But only 2% to 3% of people will develop the disease, according to the National Psoriasis Foundation (NSF). Therefore, researchers believe that psoriasis is caused by a certain combination of genes that spring into action after being exposed to a trigger. Common triggers include stress, an infection (like strep throat), and certain medications (like lithium). Cold, dry weather and sunburns may also trigger psoriasis flares.

When someone with psoriasis is exposed to a trigger, their immune system scrambles to defend itself by producing T cells, a type of white blood cell that helps ward off infections and other diseases. With psoriasis, however, T cell-production goes into overdrive, eventually causing inflammation and faster-than-usual growth of skin cells, leading to psoriasis symptoms.

The signs and symptoms of psoriasis vary depending on the type and severity of the skin disease. Some people may have one form of psoriasis, while others can have two or more.

Raised reddish patches. People with plaque psoriasis can experience a flare-up of red, raised patches. These patches can be itchy or painful or crack and bleed.

Scaly patches. Often seen in plaque psoriasis, scales are patches of built-up dead skin cells that have a silvery-white sheen. They often appear on top of raised, red patches that can be itchy or painful or crack and bleed. People with plaque psoriasis can experience a flare-up of symptoms on their scalp, knees, elbows, and lower back.

White pustules. A characteristic of pustular psoriasis, these white pus-filled blisters can cluster on the hands and feet or spread to most of the body. After the pustules appear, scaling usually follows. In people with von Zumbusch psoriasis, the pustules will dry after 24 to 48 hours, leaving the skin with a glazed appearance. In people with palmoplantar pustulosis, the pustules will turn brown, then peel, then start to crust.

Red, smooth lesions.Seen in inverse psoriasis, these very red lesions are smooth and shiny and are found in parts of the body with folds of skin, like the armpits, groin, and under the breasts. Because these lesions tend to be located in sensitive areas, they are prone to irritation from rubbing or sweating.

Red spots. A telltale sign of guttate psoriasis, these small, red spots are shaped like drops and usually appear on the torso, arms, and legs. In most cases, they arent as thick as plaque psoriasis lesions, but they can be widespread, numbering into the hundreds.

Nail changes.About 50% of people with psoriasis experience changes to their finger or toenails, including pitting (the appearance of holes in the nail), thickening, and discoloration, according to the NPF.

RELATED: 10 Things Your Nails Can Tell You About Your Health

Areas of the body normally affected by psoriasis

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There are no special diagnostic tests for psoriasis. Instead, a psoriasis diagnosis is made by a dermatologist, who will examine the skin lesions visually. In some cases, psoriasis can resemble other types of skin conditions, like eczema, so doctors may want to confirm the results with a biopsy. That involves removing some of the skin and looking at the sample under a microscope, where psoriasis tends to appear thicker than eczema.

Doctors may also take a detailed record of your familys medical history: About one-third of people with psoriasis have a first-degree relative who also has the condition. Health care providers may also try to pinpoint psoriasis triggers by asking whether their patients have been under stress lately or are taking a new medication.

Theres no one-size-fits-all psoriasis treatment, and the medications that work for some people may not work for others. The goal, however, is the same for everyone: to find psoriasis medications that can reduce or eliminate psoriasis symptoms. Here are some of the most commonly prescribed therapies.

Topical medications. A first-line form of therapy for mild to moderate conditions, topicals (in psoriasis cream, gel, and ointment forms) are applied directly to the skin in the hopes of reducing inflammation and slowing down skin cell growth. Some are available over-the-counter, like products with salicylic acid and coal tar as active ingredients, while others, like calcipotriene (a form of vitamin D3) and tazarotene (a vitamin A derivative known as a retinoid) are available by prescription. There are also special psoriasis shampoos that can help clear up scalp psoriasis; many contain coal tar and salicylic acid.

Phototherapy. Also called light therapy, phototherapy exposes a persons skin to ultraviolet light, which is thought to kill the immune cells contributing to psoriasis. Phototherapy can be administered in the form of UVB rays, a combination of UVA and UVB, or UVA rays alongside an oral or topical medication called psoralen (a treatment called PUVA). The catch: These treatments have to be done in a doctors office, a psoriasis clinic, or with a specialized phototherapy unit and usually require several visits, which can become expensive. Because indoor tanning increases the risk of skin cancer (especially melanoma), its not considered a safe substitute for phototherapy under medical supervision.

Systemic medications. If topical medications and phototherapy dont work, doctors may recommend taking systemics, or prescription drugs that affect the entire body. These meds can be taken orally or via an injection, and include cyclosporine (which suppresses immune system activity and slows skin cell growth), acitretin (an oral retinoid, or form of vitamin A, that slows down the speed at which skin cells grow and shed), and methotrexate (a medication that was originally used as a cancer treatment, but can also slow down the growth of skin cells).

Biologic drugs. Biologics contain human or animal proteins and can block certain immune cells that are involved in psoriasis. Theyre usually recommended for people with moderate to severe psoriasis and are administered via an injection or IV infusion. There are currently three types of biologics that can help treat psoriasis, all of which block immune system chemical messengers that promote inflammation called cytokines. The three types of biologics block the cytokines tumor necrosis factor alpha (TNF-alpha), interleukin 12, interleukin 23, and interleukin 17-A (IL-12, IL-23, and IL-17A, respectively).

RELATED: 21 Tips and Tricks for Treating Psoriasis

Alternative and complementary therapies. Some alternative therapiesincluding acupuncture, massage, and Reikimight help relieve certain psoriasis symptoms, like pain. They may also help control stress, a common psoriasis trigger. Other stress-relievers include meditation, mindfulness, exercise, yoga, and Tai Chi. Always talk to your doctor before beginning any alternative psoriasis treatments.

There is currently no cure for psoriasis. As a chronic autoimmune disease, most people with psoriasis will always have it. But it is possible to treat the condition. In fact, the right medications and therapies can reduce symptoms and even clear up the skin entirely in some people.

More psoriasis treatments may be available in the future. Researchers are currently trying to uncover what causes the lesions on a cellular level and how to prevent flare-ups caused by the immune system.

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For the millions of Americans who have psoriasis, the skin condition can pose many challenges. Not only can the pain and itching interfere with their ability to sleep or work, but research shows that many people with psoriasis feel unattractive; worse, if they feel self-conscious, they may withdraw from their friends and family and become isolated.

People with psoriasis are also twice as likely to be depressed as those who dont have the skin condition, according to the NPF, and they can also be more likely to have suicidal thoughts. If youre feeling a loss of energy, lack of interest in once-enjoyable activities, or an inability to focus, talk to your doctor about whether you may have depression or should see a mental health specialist.

An estimated 30% of people with psoriasis will also develop psoriatic arthritis, a disease which causes joint pain, stiffness, and swelling. Having psoriasis may also make people more likely to develop cardiovascular disease, obesity, and diabetes, according to the NPF.

RELATED: 12 Best and Worst Foods for Psoriasis

There are many ways that people living with psoriasis can manage the condition. This includes avoiding tobacco, alcohol, and unhealthy foods. Although there is no psoriasis diet, per se, eating healthy meals may help you feel better. You should also keep tabs on whether your joints feel stiff or sore or whether your nails are pitting or turning yellowtwo possible signs of psoriatic arthritis. Recognizing these symptomsand getting treatmentcan help prevent further damage to the joints.

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Anyone can develop psoriasiseven the most beautiful people on the planet. And as people who are paid to look flawless, many celebrities with psoriasis say that the skin condition delivers a serious blow to their self-esteem and fear that it can interfere with their careers.

In 2011, Kim Kardashian revealed her psoriasis diagnosis on an episode of Keeping Up With the Kardashians. Although her mother, Kris Jenner, was diagnosed with psoriasis at the age of 30, Kim was surprised to learn that she had the skin condition too. My career is doing ad campaigns and swimsuit photo shoots, she said in the episode. People dont understand the pressure on me to look perfect. Imagine what the tabloids would do to me if they saw all these spots.

Model and actress Cara Delevingne also has psoriasis, which she struggled to manage while runway modeling. She told Londons The Times in an interview that people would paint her body with foundation to cover up the patches. It was every single show, she said. People would put on gloves and not want to touch me.

Other models also struggle with psoriasis, like CariDee English, who won Americas Next Top Model in 2006. Partly in response to the hurtful tabloid headlines that called out the lesions on her legs, she posted before-and-after photos of one of her flare-ups, saying, I knew I didnt want anyone capturing my psoriasis in a way that wasnt empowering.

Other celebs who have psoriasis include golfer Phil Michelson, country singer LeAnn Rimes, and pop star Cyndi Lauper.

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Continued here:

Psoriasis – Causes, Symptoms and Treatment – Health.com …

Psoriasis | Psoriatic Arthritis | MedlinePlus

Psoriasis is a skin disease that causes itchy or sore patches of thick, red skin with silvery scales. You usually get the patches on your elbows, knees, scalp, back, face, palms and feet, but they can show up on other parts of your body. Some people who have psoriasis also get a form of arthritis called psoriatic arthritis.

A problem with your immune system causes psoriasis. In a process called cell turnover, skin cells that grow deep in your skin rise to the surface. Normally, this takes a month. In psoriasis, it happens in just days because your cells rise too fast.

Psoriasis can be hard to diagnose because it can look like other skin diseases. Your doctor might need to look at a small skin sample under a microscope.

Psoriasis can last a long time, even a lifetime. Symptoms come and go. Things that make them worse include

Psoriasis usually occurs in adults. It sometimes runs in families. Treatments include creams, medicines, and light therapy.

NIH: National Institute of Arthritis and Musculoskeletal and Skin Diseases

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Psoriasis | Psoriatic Arthritis | MedlinePlus

Human genetics | biology | Britannica.com

Human genetics, study of the inheritance of characteristics by children from parents. Inheritance in humans does not differ in any fundamental way from that in other organisms.

The study of human heredity occupies a central position in genetics. Much of this interest stems from a basic desire to know who humans are and why they are as they are. At a more practical level, an understanding of human heredity is of critical importance in the prediction, diagnosis, and treatment of diseases that have a genetic component. The quest to determine the genetic basis of human health has given rise to the field of medical genetics. In general, medicine has given focus and purpose to human genetics, so the terms medical genetics and human genetics are often considered synonymous.

Read More on This Topic

genetics: Human genetics

Some geneticists specialize in the hereditary processes of human genetics. Most of the emphasis is on understanding and treating genetic disease and genetically influenced ill health, areas collectively known as medical genetics. One broad area of activity is laboratory research dealing with the

A new era in cytogenetics, the field of investigation concerned with studies of the chromosomes, began in 1956 with the discovery by Jo Hin Tjio and Albert Levan that human somatic cells contain 23 pairs of chromosomes. Since that time the field has advanced with amazing rapidity and has demonstrated that human chromosome aberrations rank as major causes of fetal death and of tragic human diseases, many of which are accompanied by mental retardation. Since the chromosomes can be delineated only during mitosis, it is necessary to examine material in which there are many dividing cells. This can usually be accomplished by culturing cells from the blood or skin, since only the bone marrow cells (not readily sampled except during serious bone marrow disease such as leukemia) have sufficient mitoses in the absence of artificial culture. After growth, the cells are fixed on slides and then stained with a variety of DNA-specific stains that permit the delineation and identification of the chromosomes. The Denver system of chromosome classification, established in 1959, identified the chromosomes by their length and the position of the centromeres. Since then the method has been improved by the use of special staining techniques that impart unique light and dark bands to each chromosome. These bands permit the identification of chromosomal regions that are duplicated, missing, or transposed to other chromosomes.

Micrographs showing the karyotypes (i.e., the physical appearance of the chromosome) of a male and a female have been produced. In a typical micrograph the 46 human chromosomes (the diploid number) are arranged in homologous pairs, each consisting of one maternally derived and one paternally derived member. The chromosomes are all numbered except for the X and the Y chromosomes, which are the sex chromosomes. In humans, as in all mammals, the normal female has two X chromosomes and the normal male has one X chromosome and one Y chromosome. The female is thus the homogametic sex, as all her gametes normally have one X chromosome. The male is heterogametic, as he produces two types of gametesone type containing an X chromosome and the other containing a Y chromosome. There is good evidence that the Y chromosome in humans, unlike that in Drosophila, is necessary (but not sufficient) for maleness.

A human individual arises through the union of two cells, an egg from the mother and a sperm from the father. Human egg cells are barely visible to the naked eye. They are shed, usually one at a time, from the ovary into the oviducts (fallopian tubes), through which they pass into the uterus. Fertilization, the penetration of an egg by a sperm, occurs in the oviducts. This is the main event of sexual reproduction and determines the genetic constitution of the new individual.

Human sex determination is a genetic process that depends basically on the presence of the Y chromosome in the fertilized egg. This chromosome stimulates a change in the undifferentiated gonad into that of the male (a testicle). The gonadal action of the Y chromosome is mediated by a gene located near the centromere; this gene codes for the production of a cell surface molecule called the H-Y antigen. Further development of the anatomic structures, both internal and external, that are associated with maleness is controlled by hormones produced by the testicle. The sex of an individual can be thought of in three different contexts: chromosomal sex, gonadal sex, and anatomic sex. Discrepancies between these, especially the latter two, result in the development of individuals with ambiguous sex, often called hermaphrodites. The phenomenon of homosexuality is of uncertain cause and is unrelated to the above sex-determining factors. It is of interest that in the absence of a male gonad (testicle) the internal and external sex anatomy is always female, even in the absence of a female ovary. A female without ovaries will, of course, be infertile and will not experience any of the female developmental changes normally associated with puberty. Such a female will often have Turners syndrome.

If X-containing and Y-containing sperm are produced in equal numbers, then according to simple chance one would expect the sex ratio at conception (fertilization) to be half boys and half girls, or 1 : 1. Direct observation of sex ratios among newly fertilized human eggs is not yet feasible, and sex-ratio data are usually collected at the time of birth. In almost all human populations of newborns, there is a slight excess of males; about 106 boys are born for every100 girls. Throughout life, however, there is a slightly greater mortality of males; this slowly alters the sex ratio until, beyond the age of about 50 years, there is an excess of females. Studies indicate that male embryos suffer a relatively greater degree of prenatal mortality, so the sex ratio at conception might be expected to favour males even more than the 106 : 100 ratio observed at birth would suggest. Firm explanations for the apparent excess of male conceptions have not been established; it is possible that Y-containing sperm survive better within the female reproductive tract, or they may be a little more successful in reaching the egg in order to fertilize it. In any case, the sex differences are small, the statistical expectation for a boy (or girl) at any single birth still being close to one out of two.

During gestationthe period of nine months between fertilization and the birth of the infanta remarkable series of developmental changes occur. Through the process of mitosis, the total number of cells changes from 1 (the fertilized egg) to about 2 1011. In addition, these cells differentiate into hundreds of different types with specific functions (liver cells, nerve cells, muscle cells, etc.). A multitude of regulatory processes, both genetically and environmentally controlled, accomplish this differentiation. Elucidation of the exquisite timing of these processes remains one of the great challenges of human biology.

Immunity is the ability of an individual to recognize the self molecules that make up ones own body and to distinguish them from such nonself molecules as those found in infectious microorganisms and toxins. This process has a prominent genetic component. Knowledge of the genetic and molecular basis of the mammalian immune system has increased in parallel with the explosive advances made in somatic cell and molecular genetics.

There are two major components of the immune system, both originating from the same precursor stem cells. The bursa component provides B lymphocytes, a class of white blood cells that, when appropriately stimulated, differentiate into plasma cells. These latter cells produce circulating soluble proteins called antibodies or immunoglobulins. Antibodies are produced in response to substances called antigens, most of which are foreign proteins or polysaccharides. An antibody molecule can recognize a specific antigen, combine with it, and initiate its destruction. This so-called humoral immunity is accomplished through a complicated series of interactions with other molecules and cells; some of these interactions are mediated by another group of lymphocytes, the T lymphocytes, which are derived from the thymus gland. Once a B lymphocyte has been exposed to a specific antigen, it remembers the contact so that future exposure will cause an accelerated and magnified immune reaction. This is a manifestation of what has been called immunological memory.

The thymus component of the immune system centres on the thymus-derived T lymphocytes. In addition to regulating the B cells in producing humoral immunity, the T cells also directly attack cells that display foreign antigens. This process, called cellular immunity, is of great importance in protecting the body against a variety of viruses as well as cancer cells. Cellular immunity is also the chief cause of the rejection of organ transplants. The T lymphocytes provide a complex network consisting of a series of helper cells (which are antigen-specific), amplifier cells, suppressor cells, and cytotoxic (killer) cells, all of which are important in immune regulation.

One of the central problems in understanding the genetics of the immune system has been in explaining the genetic regulation of antibody production. Immunobiologists have demonstrated that the system can produce well over one million specific antibodies, each corresponding to a particular antigen. It would be difficult to envisage that each antibody is encoded by a separate gene; such an arrangement would require a disproportionate share of the entire human genome. Recombinant DNA analysis has illuminated the mechanisms by which a limited number of immunoglobulin genes can encode this vast number of antibodies.

Each antibody molecule consists of several different polypeptide chainsthe light chains (L) and the longer heavy chains (H). The latter determine to which of five different classes (IgM, IgG, IgA, IgD, or IgE) an immunoglobulin belongs. Both the L and H chains are unique among proteins in that they contain constant and variable parts. The constant parts have relatively identical amino acid sequences in any given antibody. The variable parts, on the other hand, have different amino acid sequences in each antibody molecule. It is the variable parts, then, that determine the specificity of the antibody.

Recombinant DNA studies of immunoglobulin genes in mice have revealed that the light-chain genes are encoded in four separate parts in germ-line DNA: a leader segment (L), a variable segment (V), a joining segment (J), and a constant segment (C). These segments are widely separated in the DNA of an embryonic cell, but in a mature B lymphocyte they are found in relative proximity (albeit separated by introns). The mouse has more than 200 light-chain variable region genes, only one of which will be incorporated into the proximal sequence that codes for the antibody production in a given B lymphocyte. Antibody diversity is greatly enhanced by this system, as the V and J segments rearrange and assort randomly in each B-lymphocyte precursor cell. The mechanisms by which this DNA rearrangement takes place are not clear, but transposons are undoubtedly involved. Similar combinatorial processes take place in the genes that code for the heavy chains; furthermore, both the light-chain and heavy-chain genes can undergo somatic mutations to create new antibody-coding sequences. The net effect of these combinatorial and mutational processes enables the coding of millions of specific antibody molecules from a limited number of genes. It should be stressed, however, that each B lymphocyte can produce only one antibody. It is the B lymphocyte population as a whole that produces the tremendous variety of antibodies in humans and other mammals.

Plasma cell tumours (myelomas) have made it possible to study individual antibodies, since these tumours, which are descendants of a single plasma cell, produce one antibody in abundance. Another method of obtaining large amounts of a specific antibody is by fusing a B lymphocyte with a rapidly growing cancer cell. The resultant hybrid cell, known as a hybridoma, multiplies rapidly in culture. Since the antibodies obtained from hybridomas are produced by clones derived from a single lymphocyte, they are called monoclonal antibodies.

As has been stated, cellular immunity is mediated by T lymphocytes that can recognize infected body cells, cancer cells, and the cells of a foreign transplant. The control of cellular immune reactions is provided by a linked group of genes, known as the major histocompatibility complex (MHC). These genes code for the major histocompatibility antigens, which are found on the surface of almost all nucleated somatic cells. The major histocompatibility antigens were first discovered on the leukocytes (white blood cells) and are therefore usually referred to as the HLA (human leukocyte group A) antigens.

The advent of the transplantation of human organs in the 1950s made the question of tissue compatibility between donor and recipient of vital importance, and it was in this context that the HLA antigens and the MHC were elucidated. Investigators found that the MHC resides on the short arm of chromosome 6, on four closely associated sites designated HLA-A, HLA-B, HLA-C, and HLA-D. Each locus is highly polymorphic; i.e., each is represented by a great many alleles within the human gene pool. These alleles, like those of the ABO blood group system, are expressed in codominant fashion. Because of the large number of alleles at each HLA locus, there is an extremely low probability of any two individuals (other than siblings) having identical HLA genotypes. (Since a person inherits one chromosome 6 from each parent, siblings have a 25 percent probability of having received the same paternal and maternal chromosomes 6 and thus of being HLA matched.)

Although HLA antigens are largely responsible for the rejection of organ transplants, it is obvious that the MHC did not evolve to prevent the transfer of organs from one person to another. Indeed, information obtained from the histocompatibility complex in the mouse (which is very similar in its genetic organization to that of the human) suggests that a primary function of the HLA antigens is to regulate the number of specific cytotoxic T killer cells, which have the ability to destroy virus-infected cells and cancer cells.

More is known about the genetics of the blood than about any other human tissue. One reason for this is that blood samples can be easily secured and subjected to biochemical analysis without harm or major discomfort to the person being tested. Perhaps a more cogent reason is that many chemical properties of human blood display relatively simple patterns of inheritance.

Certain chemical substances within the red blood cells (such as the ABO and MN substances noted above) may serve as antigens. When cells that contain specific antigens are introduced into the body of an experimental animal such as a rabbit, the animal responds by producing antibodies in its own blood.

In addition to the ABO and MN systems, geneticists have identified about 14 blood-type gene systems associated with other chromosomal locations. The best known of these is the Rh system. The Rh antigens are of particular importance in human medicine. Curiously, however, their existence was discovered in monkeys. When blood from the rhesus monkey (hence the designation Rh) is injected into rabbits, the rabbits produce so-called Rh antibodies that will agglutinate not only the red blood cells of the monkey but the cells of a large proportion of human beings as well. Some people (Rh-negative individuals), however, lack the Rh antigen; the proportion of such persons varies from one human population to another. Akin to data concerning the ABO system, the evidence for Rh genes indicates that only a single chromosome locus (called r) is involved and is located on chromosome 1. At least 35 Rh alleles are known for the r location; basically the Rh-negative condition is recessive.

A medical problem may arise when a woman who is Rh-negative carries a fetus that is Rh-positive. The first such child may have no difficulty, but later similar pregnancies may produce severely anemic newborn infants. Exposure to the red blood cells of the first Rh-positive fetus appears to immunize the Rh-negative mother, that is, she develops antibodies that may produce permanent (sometimes fatal) brain damage in any subsequent Rh-positive fetus. Damage arises from the scarcity of oxygen reaching the fetal brain because of the severe destruction of red blood cells. Measures are available for avoiding the severe effects of Rh incompatibility by transfusions to the fetus within the uterus; however, genetic counselling before conception is helpful so that the mother can receive Rh immunoglobulin immediately after her first and any subsequent pregnancies involving an Rh-positive fetus. This immunoglobulin effectively destroys the fetal red blood cells before the mothers immune system is stimulated. The mother thus avoids becoming actively immunized against the Rh antigen and will not produce antibodies that could attack the red blood cells of a future Rh-positive fetus.

Human serum, the fluid portion of the blood that remains after clotting, contains various proteins that have been shown to be under genetic control. Study of genetic influences has flourished since the development of precise methods for separating and identifying serum proteins. These move at different rates under the impetus of an electrical field (electrophoresis), as do proteins from many other sources (e.g., muscle or nerve). Since the composition of a protein is specified by the structure of its corresponding gene, biochemical studies based on electrophoresis permit direct study of tissue substances that are only a metabolic step or two away from the genes themselves.

Electrophoretic studies have revealed that at least one-third of the human serum proteins occur in variant forms. Many of the serum proteins are polymorphic, occurring as two or more variants with a frequency of not less than 1 percent each in a population. Patterns of polymorphic serum protein variants have been used to determine whether twins are identical (as in assessing compatibility for organ transplants) or whether two individuals are related (as in resolving paternity suits). Whether the different forms have a selective advantage is not generally known.

Much attention in the genetics of substances in the blood has been centred on serum proteins called haptoglobins, transferrins (which transport iron), and gamma globulins (a number of which are known to immunize against infectious diseases). Haptoglobins appear to relate to two common alleles at a single chromosome locus; the mode of inheritance of the other two seems more complicated, about 18 kinds of transferrins having been described. Like blood-cell antigen genes, serum-protein genes are distributed worldwide in the human population in a way that permits their use in tracing the origin and migration of different groups of people.

Hundreds of variants of hemoglobin have been identified by electrophoresis, but relatively few are frequent enough to be called polymorphisms. Of the polymorphisms, the alleles for sickle-cell and thalassemia hemoglobins produce serious disease in homozygotes, whereas others (hemoglobins C, D, and E) do not. The sickle-cell polymorphism confers a selective advantage on the heterozygote living in a malarial environment; the thalassemia polymorphism provides a similar advantage.

Read more:

Human genetics | biology | Britannica.com

Human genetics | biology | Britannica.com

Human genetics, study of the inheritance of characteristics by children from parents. Inheritance in humans does not differ in any fundamental way from that in other organisms.

The study of human heredity occupies a central position in genetics. Much of this interest stems from a basic desire to know who humans are and why they are as they are. At a more practical level, an understanding of human heredity is of critical importance in the prediction, diagnosis, and treatment of diseases that have a genetic component. The quest to determine the genetic basis of human health has given rise to the field of medical genetics. In general, medicine has given focus and purpose to human genetics, so the terms medical genetics and human genetics are often considered synonymous.

Read More on This Topic

genetics: Human genetics

Some geneticists specialize in the hereditary processes of human genetics. Most of the emphasis is on understanding and treating genetic disease and genetically influenced ill health, areas collectively known as medical genetics. One broad area of activity is laboratory research dealing with the

A new era in cytogenetics, the field of investigation concerned with studies of the chromosomes, began in 1956 with the discovery by Jo Hin Tjio and Albert Levan that human somatic cells contain 23 pairs of chromosomes. Since that time the field has advanced with amazing rapidity and has demonstrated that human chromosome aberrations rank as major causes of fetal death and of tragic human diseases, many of which are accompanied by mental retardation. Since the chromosomes can be delineated only during mitosis, it is necessary to examine material in which there are many dividing cells. This can usually be accomplished by culturing cells from the blood or skin, since only the bone marrow cells (not readily sampled except during serious bone marrow disease such as leukemia) have sufficient mitoses in the absence of artificial culture. After growth, the cells are fixed on slides and then stained with a variety of DNA-specific stains that permit the delineation and identification of the chromosomes. The Denver system of chromosome classification, established in 1959, identified the chromosomes by their length and the position of the centromeres. Since then the method has been improved by the use of special staining techniques that impart unique light and dark bands to each chromosome. These bands permit the identification of chromosomal regions that are duplicated, missing, or transposed to other chromosomes.

Micrographs showing the karyotypes (i.e., the physical appearance of the chromosome) of a male and a female have been produced. In a typical micrograph the 46 human chromosomes (the diploid number) are arranged in homologous pairs, each consisting of one maternally derived and one paternally derived member. The chromosomes are all numbered except for the X and the Y chromosomes, which are the sex chromosomes. In humans, as in all mammals, the normal female has two X chromosomes and the normal male has one X chromosome and one Y chromosome. The female is thus the homogametic sex, as all her gametes normally have one X chromosome. The male is heterogametic, as he produces two types of gametesone type containing an X chromosome and the other containing a Y chromosome. There is good evidence that the Y chromosome in humans, unlike that in Drosophila, is necessary (but not sufficient) for maleness.

A human individual arises through the union of two cells, an egg from the mother and a sperm from the father. Human egg cells are barely visible to the naked eye. They are shed, usually one at a time, from the ovary into the oviducts (fallopian tubes), through which they pass into the uterus. Fertilization, the penetration of an egg by a sperm, occurs in the oviducts. This is the main event of sexual reproduction and determines the genetic constitution of the new individual.

Human sex determination is a genetic process that depends basically on the presence of the Y chromosome in the fertilized egg. This chromosome stimulates a change in the undifferentiated gonad into that of the male (a testicle). The gonadal action of the Y chromosome is mediated by a gene located near the centromere; this gene codes for the production of a cell surface molecule called the H-Y antigen. Further development of the anatomic structures, both internal and external, that are associated with maleness is controlled by hormones produced by the testicle. The sex of an individual can be thought of in three different contexts: chromosomal sex, gonadal sex, and anatomic sex. Discrepancies between these, especially the latter two, result in the development of individuals with ambiguous sex, often called hermaphrodites. The phenomenon of homosexuality is of uncertain cause and is unrelated to the above sex-determining factors. It is of interest that in the absence of a male gonad (testicle) the internal and external sex anatomy is always female, even in the absence of a female ovary. A female without ovaries will, of course, be infertile and will not experience any of the female developmental changes normally associated with puberty. Such a female will often have Turners syndrome.

If X-containing and Y-containing sperm are produced in equal numbers, then according to simple chance one would expect the sex ratio at conception (fertilization) to be half boys and half girls, or 1 : 1. Direct observation of sex ratios among newly fertilized human eggs is not yet feasible, and sex-ratio data are usually collected at the time of birth. In almost all human populations of newborns, there is a slight excess of males; about 106 boys are born for every100 girls. Throughout life, however, there is a slightly greater mortality of males; this slowly alters the sex ratio until, beyond the age of about 50 years, there is an excess of females. Studies indicate that male embryos suffer a relatively greater degree of prenatal mortality, so the sex ratio at conception might be expected to favour males even more than the 106 : 100 ratio observed at birth would suggest. Firm explanations for the apparent excess of male conceptions have not been established; it is possible that Y-containing sperm survive better within the female reproductive tract, or they may be a little more successful in reaching the egg in order to fertilize it. In any case, the sex differences are small, the statistical expectation for a boy (or girl) at any single birth still being close to one out of two.

During gestationthe period of nine months between fertilization and the birth of the infanta remarkable series of developmental changes occur. Through the process of mitosis, the total number of cells changes from 1 (the fertilized egg) to about 2 1011. In addition, these cells differentiate into hundreds of different types with specific functions (liver cells, nerve cells, muscle cells, etc.). A multitude of regulatory processes, both genetically and environmentally controlled, accomplish this differentiation. Elucidation of the exquisite timing of these processes remains one of the great challenges of human biology.

Immunity is the ability of an individual to recognize the self molecules that make up ones own body and to distinguish them from such nonself molecules as those found in infectious microorganisms and toxins. This process has a prominent genetic component. Knowledge of the genetic and molecular basis of the mammalian immune system has increased in parallel with the explosive advances made in somatic cell and molecular genetics.

There are two major components of the immune system, both originating from the same precursor stem cells. The bursa component provides B lymphocytes, a class of white blood cells that, when appropriately stimulated, differentiate into plasma cells. These latter cells produce circulating soluble proteins called antibodies or immunoglobulins. Antibodies are produced in response to substances called antigens, most of which are foreign proteins or polysaccharides. An antibody molecule can recognize a specific antigen, combine with it, and initiate its destruction. This so-called humoral immunity is accomplished through a complicated series of interactions with other molecules and cells; some of these interactions are mediated by another group of lymphocytes, the T lymphocytes, which are derived from the thymus gland. Once a B lymphocyte has been exposed to a specific antigen, it remembers the contact so that future exposure will cause an accelerated and magnified immune reaction. This is a manifestation of what has been called immunological memory.

The thymus component of the immune system centres on the thymus-derived T lymphocytes. In addition to regulating the B cells in producing humoral immunity, the T cells also directly attack cells that display foreign antigens. This process, called cellular immunity, is of great importance in protecting the body against a variety of viruses as well as cancer cells. Cellular immunity is also the chief cause of the rejection of organ transplants. The T lymphocytes provide a complex network consisting of a series of helper cells (which are antigen-specific), amplifier cells, suppressor cells, and cytotoxic (killer) cells, all of which are important in immune regulation.

One of the central problems in understanding the genetics of the immune system has been in explaining the genetic regulation of antibody production. Immunobiologists have demonstrated that the system can produce well over one million specific antibodies, each corresponding to a particular antigen. It would be difficult to envisage that each antibody is encoded by a separate gene; such an arrangement would require a disproportionate share of the entire human genome. Recombinant DNA analysis has illuminated the mechanisms by which a limited number of immunoglobulin genes can encode this vast number of antibodies.

Each antibody molecule consists of several different polypeptide chainsthe light chains (L) and the longer heavy chains (H). The latter determine to which of five different classes (IgM, IgG, IgA, IgD, or IgE) an immunoglobulin belongs. Both the L and H chains are unique among proteins in that they contain constant and variable parts. The constant parts have relatively identical amino acid sequences in any given antibody. The variable parts, on the other hand, have different amino acid sequences in each antibody molecule. It is the variable parts, then, that determine the specificity of the antibody.

Recombinant DNA studies of immunoglobulin genes in mice have revealed that the light-chain genes are encoded in four separate parts in germ-line DNA: a leader segment (L), a variable segment (V), a joining segment (J), and a constant segment (C). These segments are widely separated in the DNA of an embryonic cell, but in a mature B lymphocyte they are found in relative proximity (albeit separated by introns). The mouse has more than 200 light-chain variable region genes, only one of which will be incorporated into the proximal sequence that codes for the antibody production in a given B lymphocyte. Antibody diversity is greatly enhanced by this system, as the V and J segments rearrange and assort randomly in each B-lymphocyte precursor cell. The mechanisms by which this DNA rearrangement takes place are not clear, but transposons are undoubtedly involved. Similar combinatorial processes take place in the genes that code for the heavy chains; furthermore, both the light-chain and heavy-chain genes can undergo somatic mutations to create new antibody-coding sequences. The net effect of these combinatorial and mutational processes enables the coding of millions of specific antibody molecules from a limited number of genes. It should be stressed, however, that each B lymphocyte can produce only one antibody. It is the B lymphocyte population as a whole that produces the tremendous variety of antibodies in humans and other mammals.

Plasma cell tumours (myelomas) have made it possible to study individual antibodies, since these tumours, which are descendants of a single plasma cell, produce one antibody in abundance. Another method of obtaining large amounts of a specific antibody is by fusing a B lymphocyte with a rapidly growing cancer cell. The resultant hybrid cell, known as a hybridoma, multiplies rapidly in culture. Since the antibodies obtained from hybridomas are produced by clones derived from a single lymphocyte, they are called monoclonal antibodies.

As has been stated, cellular immunity is mediated by T lymphocytes that can recognize infected body cells, cancer cells, and the cells of a foreign transplant. The control of cellular immune reactions is provided by a linked group of genes, known as the major histocompatibility complex (MHC). These genes code for the major histocompatibility antigens, which are found on the surface of almost all nucleated somatic cells. The major histocompatibility antigens were first discovered on the leukocytes (white blood cells) and are therefore usually referred to as the HLA (human leukocyte group A) antigens.

The advent of the transplantation of human organs in the 1950s made the question of tissue compatibility between donor and recipient of vital importance, and it was in this context that the HLA antigens and the MHC were elucidated. Investigators found that the MHC resides on the short arm of chromosome 6, on four closely associated sites designated HLA-A, HLA-B, HLA-C, and HLA-D. Each locus is highly polymorphic; i.e., each is represented by a great many alleles within the human gene pool. These alleles, like those of the ABO blood group system, are expressed in codominant fashion. Because of the large number of alleles at each HLA locus, there is an extremely low probability of any two individuals (other than siblings) having identical HLA genotypes. (Since a person inherits one chromosome 6 from each parent, siblings have a 25 percent probability of having received the same paternal and maternal chromosomes 6 and thus of being HLA matched.)

Although HLA antigens are largely responsible for the rejection of organ transplants, it is obvious that the MHC did not evolve to prevent the transfer of organs from one person to another. Indeed, information obtained from the histocompatibility complex in the mouse (which is very similar in its genetic organization to that of the human) suggests that a primary function of the HLA antigens is to regulate the number of specific cytotoxic T killer cells, which have the ability to destroy virus-infected cells and cancer cells.

More is known about the genetics of the blood than about any other human tissue. One reason for this is that blood samples can be easily secured and subjected to biochemical analysis without harm or major discomfort to the person being tested. Perhaps a more cogent reason is that many chemical properties of human blood display relatively simple patterns of inheritance.

Certain chemical substances within the red blood cells (such as the ABO and MN substances noted above) may serve as antigens. When cells that contain specific antigens are introduced into the body of an experimental animal such as a rabbit, the animal responds by producing antibodies in its own blood.

In addition to the ABO and MN systems, geneticists have identified about 14 blood-type gene systems associated with other chromosomal locations. The best known of these is the Rh system. The Rh antigens are of particular importance in human medicine. Curiously, however, their existence was discovered in monkeys. When blood from the rhesus monkey (hence the designation Rh) is injected into rabbits, the rabbits produce so-called Rh antibodies that will agglutinate not only the red blood cells of the monkey but the cells of a large proportion of human beings as well. Some people (Rh-negative individuals), however, lack the Rh antigen; the proportion of such persons varies from one human population to another. Akin to data concerning the ABO system, the evidence for Rh genes indicates that only a single chromosome locus (called r) is involved and is located on chromosome 1. At least 35 Rh alleles are known for the r location; basically the Rh-negative condition is recessive.

A medical problem may arise when a woman who is Rh-negative carries a fetus that is Rh-positive. The first such child may have no difficulty, but later similar pregnancies may produce severely anemic newborn infants. Exposure to the red blood cells of the first Rh-positive fetus appears to immunize the Rh-negative mother, that is, she develops antibodies that may produce permanent (sometimes fatal) brain damage in any subsequent Rh-positive fetus. Damage arises from the scarcity of oxygen reaching the fetal brain because of the severe destruction of red blood cells. Measures are available for avoiding the severe effects of Rh incompatibility by transfusions to the fetus within the uterus; however, genetic counselling before conception is helpful so that the mother can receive Rh immunoglobulin immediately after her first and any subsequent pregnancies involving an Rh-positive fetus. This immunoglobulin effectively destroys the fetal red blood cells before the mothers immune system is stimulated. The mother thus avoids becoming actively immunized against the Rh antigen and will not produce antibodies that could attack the red blood cells of a future Rh-positive fetus.

Human serum, the fluid portion of the blood that remains after clotting, contains various proteins that have been shown to be under genetic control. Study of genetic influences has flourished since the development of precise methods for separating and identifying serum proteins. These move at different rates under the impetus of an electrical field (electrophoresis), as do proteins from many other sources (e.g., muscle or nerve). Since the composition of a protein is specified by the structure of its corresponding gene, biochemical studies based on electrophoresis permit direct study of tissue substances that are only a metabolic step or two away from the genes themselves.

Electrophoretic studies have revealed that at least one-third of the human serum proteins occur in variant forms. Many of the serum proteins are polymorphic, occurring as two or more variants with a frequency of not less than 1 percent each in a population. Patterns of polymorphic serum protein variants have been used to determine whether twins are identical (as in assessing compatibility for organ transplants) or whether two individuals are related (as in resolving paternity suits). Whether the different forms have a selective advantage is not generally known.

Much attention in the genetics of substances in the blood has been centred on serum proteins called haptoglobins, transferrins (which transport iron), and gamma globulins (a number of which are known to immunize against infectious diseases). Haptoglobins appear to relate to two common alleles at a single chromosome locus; the mode of inheritance of the other two seems more complicated, about 18 kinds of transferrins having been described. Like blood-cell antigen genes, serum-protein genes are distributed worldwide in the human population in a way that permits their use in tracing the origin and migration of different groups of people.

Hundreds of variants of hemoglobin have been identified by electrophoresis, but relatively few are frequent enough to be called polymorphisms. Of the polymorphisms, the alleles for sickle-cell and thalassemia hemoglobins produce serious disease in homozygotes, whereas others (hemoglobins C, D, and E) do not. The sickle-cell polymorphism confers a selective advantage on the heterozygote living in a malarial environment; the thalassemia polymorphism provides a similar advantage.

Read more here:

Human genetics | biology | Britannica.com

Human genetics | biology | Britannica.com

Human genetics, study of the inheritance of characteristics by children from parents. Inheritance in humans does not differ in any fundamental way from that in other organisms.

The study of human heredity occupies a central position in genetics. Much of this interest stems from a basic desire to know who humans are and why they are as they are. At a more practical level, an understanding of human heredity is of critical importance in the prediction, diagnosis, and treatment of diseases that have a genetic component. The quest to determine the genetic basis of human health has given rise to the field of medical genetics. In general, medicine has given focus and purpose to human genetics, so the terms medical genetics and human genetics are often considered synonymous.

Read More on This Topic

genetics: Human genetics

Some geneticists specialize in the hereditary processes of human genetics. Most of the emphasis is on understanding and treating genetic disease and genetically influenced ill health, areas collectively known as medical genetics. One broad area of activity is laboratory research dealing with the

A new era in cytogenetics, the field of investigation concerned with studies of the chromosomes, began in 1956 with the discovery by Jo Hin Tjio and Albert Levan that human somatic cells contain 23 pairs of chromosomes. Since that time the field has advanced with amazing rapidity and has demonstrated that human chromosome aberrations rank as major causes of fetal death and of tragic human diseases, many of which are accompanied by mental retardation. Since the chromosomes can be delineated only during mitosis, it is necessary to examine material in which there are many dividing cells. This can usually be accomplished by culturing cells from the blood or skin, since only the bone marrow cells (not readily sampled except during serious bone marrow disease such as leukemia) have sufficient mitoses in the absence of artificial culture. After growth, the cells are fixed on slides and then stained with a variety of DNA-specific stains that permit the delineation and identification of the chromosomes. The Denver system of chromosome classification, established in 1959, identified the chromosomes by their length and the position of the centromeres. Since then the method has been improved by the use of special staining techniques that impart unique light and dark bands to each chromosome. These bands permit the identification of chromosomal regions that are duplicated, missing, or transposed to other chromosomes.

Micrographs showing the karyotypes (i.e., the physical appearance of the chromosome) of a male and a female have been produced. In a typical micrograph the 46 human chromosomes (the diploid number) are arranged in homologous pairs, each consisting of one maternally derived and one paternally derived member. The chromosomes are all numbered except for the X and the Y chromosomes, which are the sex chromosomes. In humans, as in all mammals, the normal female has two X chromosomes and the normal male has one X chromosome and one Y chromosome. The female is thus the homogametic sex, as all her gametes normally have one X chromosome. The male is heterogametic, as he produces two types of gametesone type containing an X chromosome and the other containing a Y chromosome. There is good evidence that the Y chromosome in humans, unlike that in Drosophila, is necessary (but not sufficient) for maleness.

A human individual arises through the union of two cells, an egg from the mother and a sperm from the father. Human egg cells are barely visible to the naked eye. They are shed, usually one at a time, from the ovary into the oviducts (fallopian tubes), through which they pass into the uterus. Fertilization, the penetration of an egg by a sperm, occurs in the oviducts. This is the main event of sexual reproduction and determines the genetic constitution of the new individual.

Human sex determination is a genetic process that depends basically on the presence of the Y chromosome in the fertilized egg. This chromosome stimulates a change in the undifferentiated gonad into that of the male (a testicle). The gonadal action of the Y chromosome is mediated by a gene located near the centromere; this gene codes for the production of a cell surface molecule called the H-Y antigen. Further development of the anatomic structures, both internal and external, that are associated with maleness is controlled by hormones produced by the testicle. The sex of an individual can be thought of in three different contexts: chromosomal sex, gonadal sex, and anatomic sex. Discrepancies between these, especially the latter two, result in the development of individuals with ambiguous sex, often called hermaphrodites. The phenomenon of homosexuality is of uncertain cause and is unrelated to the above sex-determining factors. It is of interest that in the absence of a male gonad (testicle) the internal and external sex anatomy is always female, even in the absence of a female ovary. A female without ovaries will, of course, be infertile and will not experience any of the female developmental changes normally associated with puberty. Such a female will often have Turners syndrome.

If X-containing and Y-containing sperm are produced in equal numbers, then according to simple chance one would expect the sex ratio at conception (fertilization) to be half boys and half girls, or 1 : 1. Direct observation of sex ratios among newly fertilized human eggs is not yet feasible, and sex-ratio data are usually collected at the time of birth. In almost all human populations of newborns, there is a slight excess of males; about 106 boys are born for every100 girls. Throughout life, however, there is a slightly greater mortality of males; this slowly alters the sex ratio until, beyond the age of about 50 years, there is an excess of females. Studies indicate that male embryos suffer a relatively greater degree of prenatal mortality, so the sex ratio at conception might be expected to favour males even more than the 106 : 100 ratio observed at birth would suggest. Firm explanations for the apparent excess of male conceptions have not been established; it is possible that Y-containing sperm survive better within the female reproductive tract, or they may be a little more successful in reaching the egg in order to fertilize it. In any case, the sex differences are small, the statistical expectation for a boy (or girl) at any single birth still being close to one out of two.

During gestationthe period of nine months between fertilization and the birth of the infanta remarkable series of developmental changes occur. Through the process of mitosis, the total number of cells changes from 1 (the fertilized egg) to about 2 1011. In addition, these cells differentiate into hundreds of different types with specific functions (liver cells, nerve cells, muscle cells, etc.). A multitude of regulatory processes, both genetically and environmentally controlled, accomplish this differentiation. Elucidation of the exquisite timing of these processes remains one of the great challenges of human biology.

Immunity is the ability of an individual to recognize the self molecules that make up ones own body and to distinguish them from such nonself molecules as those found in infectious microorganisms and toxins. This process has a prominent genetic component. Knowledge of the genetic and molecular basis of the mammalian immune system has increased in parallel with the explosive advances made in somatic cell and molecular genetics.

There are two major components of the immune system, both originating from the same precursor stem cells. The bursa component provides B lymphocytes, a class of white blood cells that, when appropriately stimulated, differentiate into plasma cells. These latter cells produce circulating soluble proteins called antibodies or immunoglobulins. Antibodies are produced in response to substances called antigens, most of which are foreign proteins or polysaccharides. An antibody molecule can recognize a specific antigen, combine with it, and initiate its destruction. This so-called humoral immunity is accomplished through a complicated series of interactions with other molecules and cells; some of these interactions are mediated by another group of lymphocytes, the T lymphocytes, which are derived from the thymus gland. Once a B lymphocyte has been exposed to a specific antigen, it remembers the contact so that future exposure will cause an accelerated and magnified immune reaction. This is a manifestation of what has been called immunological memory.

The thymus component of the immune system centres on the thymus-derived T lymphocytes. In addition to regulating the B cells in producing humoral immunity, the T cells also directly attack cells that display foreign antigens. This process, called cellular immunity, is of great importance in protecting the body against a variety of viruses as well as cancer cells. Cellular immunity is also the chief cause of the rejection of organ transplants. The T lymphocytes provide a complex network consisting of a series of helper cells (which are antigen-specific), amplifier cells, suppressor cells, and cytotoxic (killer) cells, all of which are important in immune regulation.

One of the central problems in understanding the genetics of the immune system has been in explaining the genetic regulation of antibody production. Immunobiologists have demonstrated that the system can produce well over one million specific antibodies, each corresponding to a particular antigen. It would be difficult to envisage that each antibody is encoded by a separate gene; such an arrangement would require a disproportionate share of the entire human genome. Recombinant DNA analysis has illuminated the mechanisms by which a limited number of immunoglobulin genes can encode this vast number of antibodies.

Each antibody molecule consists of several different polypeptide chainsthe light chains (L) and the longer heavy chains (H). The latter determine to which of five different classes (IgM, IgG, IgA, IgD, or IgE) an immunoglobulin belongs. Both the L and H chains are unique among proteins in that they contain constant and variable parts. The constant parts have relatively identical amino acid sequences in any given antibody. The variable parts, on the other hand, have different amino acid sequences in each antibody molecule. It is the variable parts, then, that determine the specificity of the antibody.

Recombinant DNA studies of immunoglobulin genes in mice have revealed that the light-chain genes are encoded in four separate parts in germ-line DNA: a leader segment (L), a variable segment (V), a joining segment (J), and a constant segment (C). These segments are widely separated in the DNA of an embryonic cell, but in a mature B lymphocyte they are found in relative proximity (albeit separated by introns). The mouse has more than 200 light-chain variable region genes, only one of which will be incorporated into the proximal sequence that codes for the antibody production in a given B lymphocyte. Antibody diversity is greatly enhanced by this system, as the V and J segments rearrange and assort randomly in each B-lymphocyte precursor cell. The mechanisms by which this DNA rearrangement takes place are not clear, but transposons are undoubtedly involved. Similar combinatorial processes take place in the genes that code for the heavy chains; furthermore, both the light-chain and heavy-chain genes can undergo somatic mutations to create new antibody-coding sequences. The net effect of these combinatorial and mutational processes enables the coding of millions of specific antibody molecules from a limited number of genes. It should be stressed, however, that each B lymphocyte can produce only one antibody. It is the B lymphocyte population as a whole that produces the tremendous variety of antibodies in humans and other mammals.

Plasma cell tumours (myelomas) have made it possible to study individual antibodies, since these tumours, which are descendants of a single plasma cell, produce one antibody in abundance. Another method of obtaining large amounts of a specific antibody is by fusing a B lymphocyte with a rapidly growing cancer cell. The resultant hybrid cell, known as a hybridoma, multiplies rapidly in culture. Since the antibodies obtained from hybridomas are produced by clones derived from a single lymphocyte, they are called monoclonal antibodies.

As has been stated, cellular immunity is mediated by T lymphocytes that can recognize infected body cells, cancer cells, and the cells of a foreign transplant. The control of cellular immune reactions is provided by a linked group of genes, known as the major histocompatibility complex (MHC). These genes code for the major histocompatibility antigens, which are found on the surface of almost all nucleated somatic cells. The major histocompatibility antigens were first discovered on the leukocytes (white blood cells) and are therefore usually referred to as the HLA (human leukocyte group A) antigens.

The advent of the transplantation of human organs in the 1950s made the question of tissue compatibility between donor and recipient of vital importance, and it was in this context that the HLA antigens and the MHC were elucidated. Investigators found that the MHC resides on the short arm of chromosome 6, on four closely associated sites designated HLA-A, HLA-B, HLA-C, and HLA-D. Each locus is highly polymorphic; i.e., each is represented by a great many alleles within the human gene pool. These alleles, like those of the ABO blood group system, are expressed in codominant fashion. Because of the large number of alleles at each HLA locus, there is an extremely low probability of any two individuals (other than siblings) having identical HLA genotypes. (Since a person inherits one chromosome 6 from each parent, siblings have a 25 percent probability of having received the same paternal and maternal chromosomes 6 and thus of being HLA matched.)

Although HLA antigens are largely responsible for the rejection of organ transplants, it is obvious that the MHC did not evolve to prevent the transfer of organs from one person to another. Indeed, information obtained from the histocompatibility complex in the mouse (which is very similar in its genetic organization to that of the human) suggests that a primary function of the HLA antigens is to regulate the number of specific cytotoxic T killer cells, which have the ability to destroy virus-infected cells and cancer cells.

More is known about the genetics of the blood than about any other human tissue. One reason for this is that blood samples can be easily secured and subjected to biochemical analysis without harm or major discomfort to the person being tested. Perhaps a more cogent reason is that many chemical properties of human blood display relatively simple patterns of inheritance.

Certain chemical substances within the red blood cells (such as the ABO and MN substances noted above) may serve as antigens. When cells that contain specific antigens are introduced into the body of an experimental animal such as a rabbit, the animal responds by producing antibodies in its own blood.

In addition to the ABO and MN systems, geneticists have identified about 14 blood-type gene systems associated with other chromosomal locations. The best known of these is the Rh system. The Rh antigens are of particular importance in human medicine. Curiously, however, their existence was discovered in monkeys. When blood from the rhesus monkey (hence the designation Rh) is injected into rabbits, the rabbits produce so-called Rh antibodies that will agglutinate not only the red blood cells of the monkey but the cells of a large proportion of human beings as well. Some people (Rh-negative individuals), however, lack the Rh antigen; the proportion of such persons varies from one human population to another. Akin to data concerning the ABO system, the evidence for Rh genes indicates that only a single chromosome locus (called r) is involved and is located on chromosome 1. At least 35 Rh alleles are known for the r location; basically the Rh-negative condition is recessive.

A medical problem may arise when a woman who is Rh-negative carries a fetus that is Rh-positive. The first such child may have no difficulty, but later similar pregnancies may produce severely anemic newborn infants. Exposure to the red blood cells of the first Rh-positive fetus appears to immunize the Rh-negative mother, that is, she develops antibodies that may produce permanent (sometimes fatal) brain damage in any subsequent Rh-positive fetus. Damage arises from the scarcity of oxygen reaching the fetal brain because of the severe destruction of red blood cells. Measures are available for avoiding the severe effects of Rh incompatibility by transfusions to the fetus within the uterus; however, genetic counselling before conception is helpful so that the mother can receive Rh immunoglobulin immediately after her first and any subsequent pregnancies involving an Rh-positive fetus. This immunoglobulin effectively destroys the fetal red blood cells before the mothers immune system is stimulated. The mother thus avoids becoming actively immunized against the Rh antigen and will not produce antibodies that could attack the red blood cells of a future Rh-positive fetus.

Human serum, the fluid portion of the blood that remains after clotting, contains various proteins that have been shown to be under genetic control. Study of genetic influences has flourished since the development of precise methods for separating and identifying serum proteins. These move at different rates under the impetus of an electrical field (electrophoresis), as do proteins from many other sources (e.g., muscle or nerve). Since the composition of a protein is specified by the structure of its corresponding gene, biochemical studies based on electrophoresis permit direct study of tissue substances that are only a metabolic step or two away from the genes themselves.

Electrophoretic studies have revealed that at least one-third of the human serum proteins occur in variant forms. Many of the serum proteins are polymorphic, occurring as two or more variants with a frequency of not less than 1 percent each in a population. Patterns of polymorphic serum protein variants have been used to determine whether twins are identical (as in assessing compatibility for organ transplants) or whether two individuals are related (as in resolving paternity suits). Whether the different forms have a selective advantage is not generally known.

Much attention in the genetics of substances in the blood has been centred on serum proteins called haptoglobins, transferrins (which transport iron), and gamma globulins (a number of which are known to immunize against infectious diseases). Haptoglobins appear to relate to two common alleles at a single chromosome locus; the mode of inheritance of the other two seems more complicated, about 18 kinds of transferrins having been described. Like blood-cell antigen genes, serum-protein genes are distributed worldwide in the human population in a way that permits their use in tracing the origin and migration of different groups of people.

Hundreds of variants of hemoglobin have been identified by electrophoresis, but relatively few are frequent enough to be called polymorphisms. Of the polymorphisms, the alleles for sickle-cell and thalassemia hemoglobins produce serious disease in homozygotes, whereas others (hemoglobins C, D, and E) do not. The sickle-cell polymorphism confers a selective advantage on the heterozygote living in a malarial environment; the thalassemia polymorphism provides a similar advantage.

Link:

Human genetics | biology | Britannica.com

Human genetics | biology | Britannica.com

Human genetics, study of the inheritance of characteristics by children from parents. Inheritance in humans does not differ in any fundamental way from that in other organisms.

The study of human heredity occupies a central position in genetics. Much of this interest stems from a basic desire to know who humans are and why they are as they are. At a more practical level, an understanding of human heredity is of critical importance in the prediction, diagnosis, and treatment of diseases that have a genetic component. The quest to determine the genetic basis of human health has given rise to the field of medical genetics. In general, medicine has given focus and purpose to human genetics, so the terms medical genetics and human genetics are often considered synonymous.

Read More on This Topic

genetics: Human genetics

Some geneticists specialize in the hereditary processes of human genetics. Most of the emphasis is on understanding and treating genetic disease and genetically influenced ill health, areas collectively known as medical genetics. One broad area of activity is laboratory research dealing with the

A new era in cytogenetics, the field of investigation concerned with studies of the chromosomes, began in 1956 with the discovery by Jo Hin Tjio and Albert Levan that human somatic cells contain 23 pairs of chromosomes. Since that time the field has advanced with amazing rapidity and has demonstrated that human chromosome aberrations rank as major causes of fetal death and of tragic human diseases, many of which are accompanied by mental retardation. Since the chromosomes can be delineated only during mitosis, it is necessary to examine material in which there are many dividing cells. This can usually be accomplished by culturing cells from the blood or skin, since only the bone marrow cells (not readily sampled except during serious bone marrow disease such as leukemia) have sufficient mitoses in the absence of artificial culture. After growth, the cells are fixed on slides and then stained with a variety of DNA-specific stains that permit the delineation and identification of the chromosomes. The Denver system of chromosome classification, established in 1959, identified the chromosomes by their length and the position of the centromeres. Since then the method has been improved by the use of special staining techniques that impart unique light and dark bands to each chromosome. These bands permit the identification of chromosomal regions that are duplicated, missing, or transposed to other chromosomes.

Micrographs showing the karyotypes (i.e., the physical appearance of the chromosome) of a male and a female have been produced. In a typical micrograph the 46 human chromosomes (the diploid number) are arranged in homologous pairs, each consisting of one maternally derived and one paternally derived member. The chromosomes are all numbered except for the X and the Y chromosomes, which are the sex chromosomes. In humans, as in all mammals, the normal female has two X chromosomes and the normal male has one X chromosome and one Y chromosome. The female is thus the homogametic sex, as all her gametes normally have one X chromosome. The male is heterogametic, as he produces two types of gametesone type containing an X chromosome and the other containing a Y chromosome. There is good evidence that the Y chromosome in humans, unlike that in Drosophila, is necessary (but not sufficient) for maleness.

A human individual arises through the union of two cells, an egg from the mother and a sperm from the father. Human egg cells are barely visible to the naked eye. They are shed, usually one at a time, from the ovary into the oviducts (fallopian tubes), through which they pass into the uterus. Fertilization, the penetration of an egg by a sperm, occurs in the oviducts. This is the main event of sexual reproduction and determines the genetic constitution of the new individual.

Human sex determination is a genetic process that depends basically on the presence of the Y chromosome in the fertilized egg. This chromosome stimulates a change in the undifferentiated gonad into that of the male (a testicle). The gonadal action of the Y chromosome is mediated by a gene located near the centromere; this gene codes for the production of a cell surface molecule called the H-Y antigen. Further development of the anatomic structures, both internal and external, that are associated with maleness is controlled by hormones produced by the testicle. The sex of an individual can be thought of in three different contexts: chromosomal sex, gonadal sex, and anatomic sex. Discrepancies between these, especially the latter two, result in the development of individuals with ambiguous sex, often called hermaphrodites. The phenomenon of homosexuality is of uncertain cause and is unrelated to the above sex-determining factors. It is of interest that in the absence of a male gonad (testicle) the internal and external sex anatomy is always female, even in the absence of a female ovary. A female without ovaries will, of course, be infertile and will not experience any of the female developmental changes normally associated with puberty. Such a female will often have Turners syndrome.

If X-containing and Y-containing sperm are produced in equal numbers, then according to simple chance one would expect the sex ratio at conception (fertilization) to be half boys and half girls, or 1 : 1. Direct observation of sex ratios among newly fertilized human eggs is not yet feasible, and sex-ratio data are usually collected at the time of birth. In almost all human populations of newborns, there is a slight excess of males; about 106 boys are born for every100 girls. Throughout life, however, there is a slightly greater mortality of males; this slowly alters the sex ratio until, beyond the age of about 50 years, there is an excess of females. Studies indicate that male embryos suffer a relatively greater degree of prenatal mortality, so the sex ratio at conception might be expected to favour males even more than the 106 : 100 ratio observed at birth would suggest. Firm explanations for the apparent excess of male conceptions have not been established; it is possible that Y-containing sperm survive better within the female reproductive tract, or they may be a little more successful in reaching the egg in order to fertilize it. In any case, the sex differences are small, the statistical expectation for a boy (or girl) at any single birth still being close to one out of two.

During gestationthe period of nine months between fertilization and the birth of the infanta remarkable series of developmental changes occur. Through the process of mitosis, the total number of cells changes from 1 (the fertilized egg) to about 2 1011. In addition, these cells differentiate into hundreds of different types with specific functions (liver cells, nerve cells, muscle cells, etc.). A multitude of regulatory processes, both genetically and environmentally controlled, accomplish this differentiation. Elucidation of the exquisite timing of these processes remains one of the great challenges of human biology.

Immunity is the ability of an individual to recognize the self molecules that make up ones own body and to distinguish them from such nonself molecules as those found in infectious microorganisms and toxins. This process has a prominent genetic component. Knowledge of the genetic and molecular basis of the mammalian immune system has increased in parallel with the explosive advances made in somatic cell and molecular genetics.

There are two major components of the immune system, both originating from the same precursor stem cells. The bursa component provides B lymphocytes, a class of white blood cells that, when appropriately stimulated, differentiate into plasma cells. These latter cells produce circulating soluble proteins called antibodies or immunoglobulins. Antibodies are produced in response to substances called antigens, most of which are foreign proteins or polysaccharides. An antibody molecule can recognize a specific antigen, combine with it, and initiate its destruction. This so-called humoral immunity is accomplished through a complicated series of interactions with other molecules and cells; some of these interactions are mediated by another group of lymphocytes, the T lymphocytes, which are derived from the thymus gland. Once a B lymphocyte has been exposed to a specific antigen, it remembers the contact so that future exposure will cause an accelerated and magnified immune reaction. This is a manifestation of what has been called immunological memory.

The thymus component of the immune system centres on the thymus-derived T lymphocytes. In addition to regulating the B cells in producing humoral immunity, the T cells also directly attack cells that display foreign antigens. This process, called cellular immunity, is of great importance in protecting the body against a variety of viruses as well as cancer cells. Cellular immunity is also the chief cause of the rejection of organ transplants. The T lymphocytes provide a complex network consisting of a series of helper cells (which are antigen-specific), amplifier cells, suppressor cells, and cytotoxic (killer) cells, all of which are important in immune regulation.

One of the central problems in understanding the genetics of the immune system has been in explaining the genetic regulation of antibody production. Immunobiologists have demonstrated that the system can produce well over one million specific antibodies, each corresponding to a particular antigen. It would be difficult to envisage that each antibody is encoded by a separate gene; such an arrangement would require a disproportionate share of the entire human genome. Recombinant DNA analysis has illuminated the mechanisms by which a limited number of immunoglobulin genes can encode this vast number of antibodies.

Each antibody molecule consists of several different polypeptide chainsthe light chains (L) and the longer heavy chains (H). The latter determine to which of five different classes (IgM, IgG, IgA, IgD, or IgE) an immunoglobulin belongs. Both the L and H chains are unique among proteins in that they contain constant and variable parts. The constant parts have relatively identical amino acid sequences in any given antibody. The variable parts, on the other hand, have different amino acid sequences in each antibody molecule. It is the variable parts, then, that determine the specificity of the antibody.

Recombinant DNA studies of immunoglobulin genes in mice have revealed that the light-chain genes are encoded in four separate parts in germ-line DNA: a leader segment (L), a variable segment (V), a joining segment (J), and a constant segment (C). These segments are widely separated in the DNA of an embryonic cell, but in a mature B lymphocyte they are found in relative proximity (albeit separated by introns). The mouse has more than 200 light-chain variable region genes, only one of which will be incorporated into the proximal sequence that codes for the antibody production in a given B lymphocyte. Antibody diversity is greatly enhanced by this system, as the V and J segments rearrange and assort randomly in each B-lymphocyte precursor cell. The mechanisms by which this DNA rearrangement takes place are not clear, but transposons are undoubtedly involved. Similar combinatorial processes take place in the genes that code for the heavy chains; furthermore, both the light-chain and heavy-chain genes can undergo somatic mutations to create new antibody-coding sequences. The net effect of these combinatorial and mutational processes enables the coding of millions of specific antibody molecules from a limited number of genes. It should be stressed, however, that each B lymphocyte can produce only one antibody. It is the B lymphocyte population as a whole that produces the tremendous variety of antibodies in humans and other mammals.

Plasma cell tumours (myelomas) have made it possible to study individual antibodies, since these tumours, which are descendants of a single plasma cell, produce one antibody in abundance. Another method of obtaining large amounts of a specific antibody is by fusing a B lymphocyte with a rapidly growing cancer cell. The resultant hybrid cell, known as a hybridoma, multiplies rapidly in culture. Since the antibodies obtained from hybridomas are produced by clones derived from a single lymphocyte, they are called monoclonal antibodies.

As has been stated, cellular immunity is mediated by T lymphocytes that can recognize infected body cells, cancer cells, and the cells of a foreign transplant. The control of cellular immune reactions is provided by a linked group of genes, known as the major histocompatibility complex (MHC). These genes code for the major histocompatibility antigens, which are found on the surface of almost all nucleated somatic cells. The major histocompatibility antigens were first discovered on the leukocytes (white blood cells) and are therefore usually referred to as the HLA (human leukocyte group A) antigens.

The advent of the transplantation of human organs in the 1950s made the question of tissue compatibility between donor and recipient of vital importance, and it was in this context that the HLA antigens and the MHC were elucidated. Investigators found that the MHC resides on the short arm of chromosome 6, on four closely associated sites designated HLA-A, HLA-B, HLA-C, and HLA-D. Each locus is highly polymorphic; i.e., each is represented by a great many alleles within the human gene pool. These alleles, like those of the ABO blood group system, are expressed in codominant fashion. Because of the large number of alleles at each HLA locus, there is an extremely low probability of any two individuals (other than siblings) having identical HLA genotypes. (Since a person inherits one chromosome 6 from each parent, siblings have a 25 percent probability of having received the same paternal and maternal chromosomes 6 and thus of being HLA matched.)

Although HLA antigens are largely responsible for the rejection of organ transplants, it is obvious that the MHC did not evolve to prevent the transfer of organs from one person to another. Indeed, information obtained from the histocompatibility complex in the mouse (which is very similar in its genetic organization to that of the human) suggests that a primary function of the HLA antigens is to regulate the number of specific cytotoxic T killer cells, which have the ability to destroy virus-infected cells and cancer cells.

More is known about the genetics of the blood than about any other human tissue. One reason for this is that blood samples can be easily secured and subjected to biochemical analysis without harm or major discomfort to the person being tested. Perhaps a more cogent reason is that many chemical properties of human blood display relatively simple patterns of inheritance.

Certain chemical substances within the red blood cells (such as the ABO and MN substances noted above) may serve as antigens. When cells that contain specific antigens are introduced into the body of an experimental animal such as a rabbit, the animal responds by producing antibodies in its own blood.

In addition to the ABO and MN systems, geneticists have identified about 14 blood-type gene systems associated with other chromosomal locations. The best known of these is the Rh system. The Rh antigens are of particular importance in human medicine. Curiously, however, their existence was discovered in monkeys. When blood from the rhesus monkey (hence the designation Rh) is injected into rabbits, the rabbits produce so-called Rh antibodies that will agglutinate not only the red blood cells of the monkey but the cells of a large proportion of human beings as well. Some people (Rh-negative individuals), however, lack the Rh antigen; the proportion of such persons varies from one human population to another. Akin to data concerning the ABO system, the evidence for Rh genes indicates that only a single chromosome locus (called r) is involved and is located on chromosome 1. At least 35 Rh alleles are known for the r location; basically the Rh-negative condition is recessive.

A medical problem may arise when a woman who is Rh-negative carries a fetus that is Rh-positive. The first such child may have no difficulty, but later similar pregnancies may produce severely anemic newborn infants. Exposure to the red blood cells of the first Rh-positive fetus appears to immunize the Rh-negative mother, that is, she develops antibodies that may produce permanent (sometimes fatal) brain damage in any subsequent Rh-positive fetus. Damage arises from the scarcity of oxygen reaching the fetal brain because of the severe destruction of red blood cells. Measures are available for avoiding the severe effects of Rh incompatibility by transfusions to the fetus within the uterus; however, genetic counselling before conception is helpful so that the mother can receive Rh immunoglobulin immediately after her first and any subsequent pregnancies involving an Rh-positive fetus. This immunoglobulin effectively destroys the fetal red blood cells before the mothers immune system is stimulated. The mother thus avoids becoming actively immunized against the Rh antigen and will not produce antibodies that could attack the red blood cells of a future Rh-positive fetus.

Human serum, the fluid portion of the blood that remains after clotting, contains various proteins that have been shown to be under genetic control. Study of genetic influences has flourished since the development of precise methods for separating and identifying serum proteins. These move at different rates under the impetus of an electrical field (electrophoresis), as do proteins from many other sources (e.g., muscle or nerve). Since the composition of a protein is specified by the structure of its corresponding gene, biochemical studies based on electrophoresis permit direct study of tissue substances that are only a metabolic step or two away from the genes themselves.

Electrophoretic studies have revealed that at least one-third of the human serum proteins occur in variant forms. Many of the serum proteins are polymorphic, occurring as two or more variants with a frequency of not less than 1 percent each in a population. Patterns of polymorphic serum protein variants have been used to determine whether twins are identical (as in assessing compatibility for organ transplants) or whether two individuals are related (as in resolving paternity suits). Whether the different forms have a selective advantage is not generally known.

Much attention in the genetics of substances in the blood has been centred on serum proteins called haptoglobins, transferrins (which transport iron), and gamma globulins (a number of which are known to immunize against infectious diseases). Haptoglobins appear to relate to two common alleles at a single chromosome locus; the mode of inheritance of the other two seems more complicated, about 18 kinds of transferrins having been described. Like blood-cell antigen genes, serum-protein genes are distributed worldwide in the human population in a way that permits their use in tracing the origin and migration of different groups of people.

Hundreds of variants of hemoglobin have been identified by electrophoresis, but relatively few are frequent enough to be called polymorphisms. Of the polymorphisms, the alleles for sickle-cell and thalassemia hemoglobins produce serious disease in homozygotes, whereas others (hemoglobins C, D, and E) do not. The sickle-cell polymorphism confers a selective advantage on the heterozygote living in a malarial environment; the thalassemia polymorphism provides a similar advantage.

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Human genetics | biology | Britannica.com

Psoriasis | Psoriatic Arthritis | MedlinePlus

Psoriasis is a skin disease that causes itchy or sore patches of thick, red skin with silvery scales. You usually get the patches on your elbows, knees, scalp, back, face, palms and feet, but they can show up on other parts of your body. Some people who have psoriasis also get a form of arthritis called psoriatic arthritis.

A problem with your immune system causes psoriasis. In a process called cell turnover, skin cells that grow deep in your skin rise to the surface. Normally, this takes a month. In psoriasis, it happens in just days because your cells rise too fast.

Psoriasis can be hard to diagnose because it can look like other skin diseases. Your doctor might need to look at a small skin sample under a microscope.

Psoriasis can last a long time, even a lifetime. Symptoms come and go. Things that make them worse include

Psoriasis usually occurs in adults. It sometimes runs in families. Treatments include creams, medicines, and light therapy.

NIH: National Institute of Arthritis and Musculoskeletal and Skin Diseases

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Psoriasis | Psoriatic Arthritis | MedlinePlus

Human genetics | biology | Britannica.com

Human genetics, study of the inheritance of characteristics by children from parents. Inheritance in humans does not differ in any fundamental way from that in other organisms.

The study of human heredity occupies a central position in genetics. Much of this interest stems from a basic desire to know who humans are and why they are as they are. At a more practical level, an understanding of human heredity is of critical importance in the prediction, diagnosis, and treatment of diseases that have a genetic component. The quest to determine the genetic basis of human health has given rise to the field of medical genetics. In general, medicine has given focus and purpose to human genetics, so the terms medical genetics and human genetics are often considered synonymous.

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genetics: Human genetics

human traits such as behaviour. Some geneticists specialize in the hereditary processes of human genetics. Most of the emphasis is on understanding and treating genetic disease and genetically influenced ill health, areas collectively known as medical genetics. One broad area of activity is laboratory research dealing with the

A new era in cytogenetics, the field of investigation concerned with studies of the chromosomes, began in 1956 with the discovery by Jo Hin Tjio and Albert Levan that human somatic cells contain 23 pairs of chromosomes. Since that time the field has advanced with amazing rapidity and has demonstrated that human chromosome aberrations rank as major causes of fetal death and of tragic human diseases, many of which are accompanied by mental retardation. Since the chromosomes can be delineated only during mitosis, it is necessary to examine material in which there are many dividing cells. This can usually be accomplished by culturing cells from the blood or skin, since only the bone marrow cells (not readily sampled except during serious bone marrow disease such as leukemia) have sufficient mitoses in the absence of artificial culture. After growth, the cells are fixed on slides and then stained with a variety of DNA-specific stains that permit the delineation and identification of the chromosomes. The Denver system of chromosome classification, established in 1959, identified the chromosomes by their length and the position of the centromeres. Since then the method has been improved by the use of special staining techniques that impart unique light and dark bands to each chromosome. These bands permit the identification of chromosomal regions that are duplicated, missing, or transposed to other chromosomes.

Micrographs showing the karyotypes (i.e., the physical appearance of the chromosome) of a male and a female have been produced. In a typical micrograph the 46 human chromosomes (the diploid number) are arranged in homologous pairs, each consisting of one maternally derived and one paternally derived member. The chromosomes are all numbered except for the X and the Y chromosomes, which are the sex chromosomes. In humans, as in all mammals, the normal female has two X chromosomes and the normal male has one X chromosome and one Y chromosome. The female is thus the homogametic sex, as all her gametes normally have one X chromosome. The male is heterogametic, as he produces two types of gametesone type containing an X chromosome and the other containing a Y chromosome. There is good evidence that the Y chromosome in humans, unlike that in Drosophila, is necessary (but not sufficient) for maleness.

A human individual arises through the union of two cells, an egg from the mother and a sperm from the father. Human egg cells are barely visible to the naked eye. They are shed, usually one at a time, from the ovary into the oviducts (fallopian tubes), through which they pass into the uterus. Fertilization, the penetration of an egg by a sperm, occurs in the oviducts. This is the main event of sexual reproduction and determines the genetic constitution of the new individual.

Human sex determination is a genetic process that depends basically on the presence of the Y chromosome in the fertilized egg. This chromosome stimulates a change in the undifferentiated gonad into that of the male (a testicle). The gonadal action of the Y chromosome is mediated by a gene located near the centromere; this gene codes for the production of a cell surface molecule called the H-Y antigen. Further development of the anatomic structures, both internal and external, that are associated with maleness is controlled by hormones produced by the testicle. The sex of an individual can be thought of in three different contexts: chromosomal sex, gonadal sex, and anatomic sex. Discrepancies between these, especially the latter two, result in the development of individuals with ambiguous sex, often called hermaphrodites. The phenomenon of homosexuality is of uncertain cause and is unrelated to the above sex-determining factors. It is of interest that in the absence of a male gonad (testicle) the internal and external sex anatomy is always female, even in the absence of a female ovary. A female without ovaries will, of course, be infertile and will not experience any of the female developmental changes normally associated with puberty. Such a female will often have Turners syndrome.

If X-containing and Y-containing sperm are produced in equal numbers, then according to simple chance one would expect the sex ratio at conception (fertilization) to be half boys and half girls, or 1 : 1. Direct observation of sex ratios among newly fertilized human eggs is not yet feasible, and sex-ratio data are usually collected at the time of birth. In almost all human populations of newborns, there is a slight excess of males; about 106 boys are born for every100 girls. Throughout life, however, there is a slightly greater mortality of males; this slowly alters the sex ratio until, beyond the age of about 50 years, there is an excess of females. Studies indicate that male embryos suffer a relatively greater degree of prenatal mortality, so the sex ratio at conception might be expected to favour males even more than the 106 : 100 ratio observed at birth would suggest. Firm explanations for the apparent excess of male conceptions have not been established; it is possible that Y-containing sperm survive better within the female reproductive tract, or they may be a little more successful in reaching the egg in order to fertilize it. In any case, the sex differences are small, the statistical expectation for a boy (or girl) at any single birth still being close to one out of two.

During gestationthe period of nine months between fertilization and the birth of the infanta remarkable series of developmental changes occur. Through the process of mitosis, the total number of cells changes from 1 (the fertilized egg) to about 2 1011. In addition, these cells differentiate into hundreds of different types with specific functions (liver cells, nerve cells, muscle cells, etc.). A multitude of regulatory processes, both genetically and environmentally controlled, accomplish this differentiation. Elucidation of the exquisite timing of these processes remains one of the great challenges of human biology.

Immunity is the ability of an individual to recognize the self molecules that make up ones own body and to distinguish them from such nonself molecules as those found in infectious microorganisms and toxins. This process has a prominent genetic component. Knowledge of the genetic and molecular basis of the mammalian immune system has increased in parallel with the explosive advances made in somatic cell and molecular genetics.

There are two major components of the immune system, both originating from the same precursor stem cells. The bursa component provides B lymphocytes, a class of white blood cells that, when appropriately stimulated, differentiate into plasma cells. These latter cells produce circulating soluble proteins called antibodies or immunoglobulins. Antibodies are produced in response to substances called antigens, most of which are foreign proteins or polysaccharides. An antibody molecule can recognize a specific antigen, combine with it, and initiate its destruction. This so-called humoral immunity is accomplished through a complicated series of interactions with other molecules and cells; some of these interactions are mediated by another group of lymphocytes, the T lymphocytes, which are derived from the thymus gland. Once a B lymphocyte has been exposed to a specific antigen, it remembers the contact so that future exposure will cause an accelerated and magnified immune reaction. This is a manifestation of what has been called immunological memory.

The thymus component of the immune system centres on the thymus-derived T lymphocytes. In addition to regulating the B cells in producing humoral immunity, the T cells also directly attack cells that display foreign antigens. This process, called cellular immunity, is of great importance in protecting the body against a variety of viruses as well as cancer cells. Cellular immunity is also the chief cause of the rejection of organ transplants. The T lymphocytes provide a complex network consisting of a series of helper cells (which are antigen-specific), amplifier cells, suppressor cells, and cytotoxic (killer) cells, all of which are important in immune regulation.

One of the central problems in understanding the genetics of the immune system has been in explaining the genetic regulation of antibody production. Immunobiologists have demonstrated that the system can produce well over one million specific antibodies, each corresponding to a particular antigen. It would be difficult to envisage that each antibody is encoded by a separate gene; such an arrangement would require a disproportionate share of the entire human genome. Recombinant DNA analysis has illuminated the mechanisms by which a limited number of immunoglobulin genes can encode this vast number of antibodies.

Each antibody molecule consists of several different polypeptide chainsthe light chains (L) and the longer heavy chains (H). The latter determine to which of five different classes (IgM, IgG, IgA, IgD, or IgE) an immunoglobulin belongs. Both the L and H chains are unique among proteins in that they contain constant and variable parts. The constant parts have relatively identical amino acid sequences in any given antibody. The variable parts, on the other hand, have different amino acid sequences in each antibody molecule. It is the variable parts, then, that determine the specificity of the antibody.

Recombinant DNA studies of immunoglobulin genes in mice have revealed that the light-chain genes are encoded in four separate parts in germ-line DNA: a leader segment (L), a variable segment (V), a joining segment (J), and a constant segment (C). These segments are widely separated in the DNA of an embryonic cell, but in a mature B lymphocyte they are found in relative proximity (albeit separated by introns). The mouse has more than 200 light-chain variable region genes, only one of which will be incorporated into the proximal sequence that codes for the antibody production in a given B lymphocyte. Antibody diversity is greatly enhanced by this system, as the V and J segments rearrange and assort randomly in each B-lymphocyte precursor cell. The mechanisms by which this DNA rearrangement takes place are not clear, but transposons are undoubtedly involved. Similar combinatorial processes take place in the genes that code for the heavy chains; furthermore, both the light-chain and heavy-chain genes can undergo somatic mutations to create new antibody-coding sequences. The net effect of these combinatorial and mutational processes enables the coding of millions of specific antibody molecules from a limited number of genes. It should be stressed, however, that each B lymphocyte can produce only one antibody. It is the B lymphocyte population as a whole that produces the tremendous variety of antibodies in humans and other mammals.

Plasma cell tumours (myelomas) have made it possible to study individual antibodies, since these tumours, which are descendants of a single plasma cell, produce one antibody in abundance. Another method of obtaining large amounts of a specific antibody is by fusing a B lymphocyte with a rapidly growing cancer cell. The resultant hybrid cell, known as a hybridoma, multiplies rapidly in culture. Since the antibodies obtained from hybridomas are produced by clones derived from a single lymphocyte, they are called monoclonal antibodies.

As has been stated, cellular immunity is mediated by T lymphocytes that can recognize infected body cells, cancer cells, and the cells of a foreign transplant. The control of cellular immune reactions is provided by a linked group of genes, known as the major histocompatibility complex (MHC). These genes code for the major histocompatibility antigens, which are found on the surface of almost all nucleated somatic cells. The major histocompatibility antigens were first discovered on the leukocytes (white blood cells) and are therefore usually referred to as the HLA (human leukocyte group A) antigens.

The advent of the transplantation of human organs in the 1950s made the question of tissue compatibility between donor and recipient of vital importance, and it was in this context that the HLA antigens and the MHC were elucidated. Investigators found that the MHC resides on the short arm of chromosome 6, on four closely associated sites designated HLA-A, HLA-B, HLA-C, and HLA-D. Each locus is highly polymorphic; i.e., each is represented by a great many alleles within the human gene pool. These alleles, like those of the ABO blood group system, are expressed in codominant fashion. Because of the large number of alleles at each HLA locus, there is an extremely low probability of any two individuals (other than siblings) having identical HLA genotypes. (Since a person inherits one chromosome 6 from each parent, siblings have a 25 percent probability of having received the same paternal and maternal chromosomes 6 and thus of being HLA matched.)

Although HLA antigens are largely responsible for the rejection of organ transplants, it is obvious that the MHC did not evolve to prevent the transfer of organs from one person to another. Indeed, information obtained from the histocompatibility complex in the mouse (which is very similar in its genetic organization to that of the human) suggests that a primary function of the HLA antigens is to regulate the number of specific cytotoxic T killer cells, which have the ability to destroy virus-infected cells and cancer cells.

More is known about the genetics of the blood than about any other human tissue. One reason for this is that blood samples can be easily secured and subjected to biochemical analysis without harm or major discomfort to the person being tested. Perhaps a more cogent reason is that many chemical properties of human blood display relatively simple patterns of inheritance.

Certain chemical substances within the red blood cells (such as the ABO and MN substances noted above) may serve as antigens. When cells that contain specific antigens are introduced into the body of an experimental animal such as a rabbit, the animal responds by producing antibodies in its own blood.

In addition to the ABO and MN systems, geneticists have identified about 14 blood-type gene systems associated with other chromosomal locations. The best known of these is the Rh system. The Rh antigens are of particular importance in human medicine. Curiously, however, their existence was discovered in monkeys. When blood from the rhesus monkey (hence the designation Rh) is injected into rabbits, the rabbits produce so-called Rh antibodies that will agglutinate not only the red blood cells of the monkey but the cells of a large proportion of human beings as well. Some people (Rh-negative individuals), however, lack the Rh antigen; the proportion of such persons varies from one human population to another. Akin to data concerning the ABO system, the evidence for Rh genes indicates that only a single chromosome locus (called r) is involved and is located on chromosome 1. At least 35 Rh alleles are known for the r location; basically the Rh-negative condition is recessive.

A medical problem may arise when a woman who is Rh-negative carries a fetus that is Rh-positive. The first such child may have no difficulty, but later similar pregnancies may produce severely anemic newborn infants. Exposure to the red blood cells of the first Rh-positive fetus appears to immunize the Rh-negative mother, that is, she develops antibodies that may produce permanent (sometimes fatal) brain damage in any subsequent Rh-positive fetus. Damage arises from the scarcity of oxygen reaching the fetal brain because of the severe destruction of red blood cells. Measures are available for avoiding the severe effects of Rh incompatibility by transfusions to the fetus within the uterus; however, genetic counselling before conception is helpful so that the mother can receive Rh immunoglobulin immediately after her first and any subsequent pregnancies involving an Rh-positive fetus. This immunoglobulin effectively destroys the fetal red blood cells before the mothers immune system is stimulated. The mother thus avoids becoming actively immunized against the Rh antigen and will not produce antibodies that could attack the red blood cells of a future Rh-positive fetus.

Human serum, the fluid portion of the blood that remains after clotting, contains various proteins that have been shown to be under genetic control. Study of genetic influences has flourished since the development of precise methods for separating and identifying serum proteins. These move at different rates under the impetus of an electrical field (electrophoresis), as do proteins from many other sources (e.g., muscle or nerve). Since the composition of a protein is specified by the structure of its corresponding gene, biochemical studies based on electrophoresis permit direct study of tissue substances that are only a metabolic step or two away from the genes themselves.

Electrophoretic studies have revealed that at least one-third of the human serum proteins occur in variant forms. Many of the serum proteins are polymorphic, occurring as two or more variants with a frequency of not less than 1 percent each in a population. Patterns of polymorphic serum protein variants have been used to determine whether twins are identical (as in assessing compatibility for organ transplants) or whether two individuals are related (as in resolving paternity suits). Whether the different forms have a selective advantage is not generally known.

Much attention in the genetics of substances in the blood has been centred on serum proteins called haptoglobins, transferrins (which transport iron), and gamma globulins (a number of which are known to immunize against infectious diseases). Haptoglobins appear to relate to two common alleles at a single chromosome locus; the mode of inheritance of the other two seems more complicated, about 18 kinds of transferrins having been described. Like blood-cell antigen genes, serum-protein genes are distributed worldwide in the human population in a way that permits their use in tracing the origin and migration of different groups of people.

Hundreds of variants of hemoglobin have been identified by electrophoresis, but relatively few are frequent enough to be called polymorphisms. Of the polymorphisms, the alleles for sickle-cell and thalassemia hemoglobins produce serious disease in homozygotes, whereas others (hemoglobins C, D, and E) do not. The sickle-cell polymorphism confers a selective advantage on the heterozygote living in a malarial environment; the thalassemia polymorphism provides a similar advantage.

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Human genetics | biology | Britannica.com

Psoriasis – Causes, Symptoms and Treatment – Health.com …

Jump to: Types | Causes | Symptoms | Diagnosis | Treatment | Living with Psoriasis | Celebrities with Psoriasis

Psoriasis is a disease in which red, scaly patches form on the skin, typically on the elbows, knees, or scalp. An estimated 7.5 million people in the United States will develop the disease, most of them between the ages of 15 and 30. Many people with psoriasis experience pain, discomfort, and self-esteem problems that can interfere with their work and social life.

Although the exact cause of psoriasis is unknown, researchers say the disease is largely geneticits caused by a combination of genes that send the immune system into overdrive, triggering the rapid growth of skin cells that form patches and lesions.

A dermatologist can likely tell the difference between psoriasis and eczema, but to the untrained eye, these skin conditions can appear similar. Generally speaking, psoriasis appears as thick, red patches that have a scaly buildup on top, according to the American Academy of Dermatology (AAD). These lesions are usually well defined, whereas eczema tends to cause a rash and be accompanied by an intense itch.

In addition, psoriasis tends to occur on the outside of the knees and elbows, and on the lower back and scalp; eczema usually covers the elbow and knee creases and the neck or face.

Research published in 2015 in the Journal of Clinical Medicine suggested that infants and children with psoriasis may be particularly likely to be misdiagnosed with eczema because they may have less scaling than adults.

RELATED: Whats That Rash?

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Psoriasis can range in severity, from mild patches to severe lesions that can affect more than 5% of the skin. There are five types of the disease: plaque psoriasis, pustular psoriasis, guttate psoriasis, inverse psoriasis, and erythrodermic psoriasis. Some people will have one form, whereas others will have two or more.

Plaque psoriasis appears as red patches with silvery white scales, or buildup of dead skin cells, called plaques. Its the most common type of psoriasis, affecting up to 90% of all people with the disease, according to the AAD. Most often found on the scalp, elbows, lower back, and knees, the plaques themselves will be raised and have clear edges; they may also itch, crack, or bleed.

Pustular psoriasis is a form of psoriasis in which white pustules (or bumps filled with white pus) appear on the skin. In a typical cycle, the skin will turn red, break out in pustules, and then develop scales. There are three types of pustular psoriasis: von Zumbusch pustular psoriasis (which appears abruptly and can be accompanied with fever, chills, and dehydration), palmoplantar pustulosis (which appears on the soles of the feet and the hands), and acropustulosis (a rare form of psoriasis that forms on the ends of the fingers or toes).

Guttate psoriasis is a type of psoriasis that appears as red, scaly teardrop-shaped spots. (The word guttate is Latin for drop.) During a flare-up, hundreds of lesions can form on the arms, legs, and torso, although they can also appear on the face, ears, and scalp. Guttate is the second most common type of psoriasis, occurring in about 10% of all people with the disease. Its most likely to appear in people who are younger than 30, oftentimes after they develop an infection like strep throat.

Inverse psoriasis is a type of psoriasis that appears as smooth, bright red lesions in the armpit, groin, and other areas with folds of skin. Because these regions of the body are prone to sweating and rubbing, inverse psoriasis can be particularly irritating and hard to treat.

Erythrodermic psoriasis is rare but can require immediate treatment or even hospitalization. The lesions look like large sheets rather than small spots, as if the area has been burned, and tend to be severely itchy and painful. A flare-up can trigger swelling, infection, and increased heart rate.

Psoriasis is not contagiousits a genetic, autoimmune disease. Psoriasis lesions cannot infect other people; likewise, people cant catch psoriasis from someone else, whether through touching, sexual contact, or swimming in the same pool. Its unclear, however, whether a majority of the general public is aware of this fact. In a small 2015 survey in the Journal of the American Academy of Dermatology, about 60% of people said they thought that psoriasis was infectious, while 41% said they thought the lesions looked contagious.

RELATED: 14 Ways to Manage Your Psoriasis

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The simplest answer to the question of what causes psoriasis: your genetics. An estimated 10% of people inherit at least one of the genes that can cause psoriasis. (There are as many as 25 genetic mutations that make someone more likely to develop psoriasis.) But only 2% to 3% of people will develop the disease, according to the National Psoriasis Foundation (NSF). Therefore, researchers believe that psoriasis is caused by a certain combination of genes that spring into action after being exposed to a trigger. Common triggers include stress, an infection (like strep throat), and certain medications (like lithium). Cold, dry weather and sunburns may also trigger psoriasis flares.

When someone with psoriasis is exposed to a trigger, their immune system scrambles to defend itself by producing T cells, a type of white blood cell that helps ward off infections and other diseases. With psoriasis, however, T cell-production goes into overdrive, eventually causing inflammation and faster-than-usual growth of skin cells, leading to psoriasis symptoms.

The signs and symptoms of psoriasis vary depending on the type and severity of the skin disease. Some people may have one form of psoriasis, while others can have two or more.

Raised reddish patches. People with plaque psoriasis can experience a flare-up of red, raised patches. These patches can be itchy or painful or crack and bleed.

Scaly patches. Often seen in plaque psoriasis, scales are patches of built-up dead skin cells that have a silvery-white sheen. They often appear on top of raised, red patches that can be itchy or painful or crack and bleed. People with plaque psoriasis can experience a flare-up of symptoms on their scalp, knees, elbows, and lower back.

White pustules. A characteristic of pustular psoriasis, these white pus-filled blisters can cluster on the hands and feet or spread to most of the body. After the pustules appear, scaling usually follows. In people with von Zumbusch psoriasis, the pustules will dry after 24 to 48 hours, leaving the skin with a glazed appearance. In people with palmoplantar pustulosis, the pustules will turn brown, then peel, then start to crust.

Red, smooth lesions.Seen in inverse psoriasis, these very red lesions are smooth and shiny and are found in parts of the body with folds of skin, like the armpits, groin, and under the breasts. Because these lesions tend to be located in sensitive areas, they are prone to irritation from rubbing or sweating.

Red spots. A telltale sign of guttate psoriasis, these small, red spots are shaped like drops and usually appear on the torso, arms, and legs. In most cases, they arent as thick as plaque psoriasis lesions, but they can be widespread, numbering into the hundreds.

Nail changes.About 50% of people with psoriasis experience changes to their finger or toenails, including pitting (the appearance of holes in the nail), thickening, and discoloration, according to the NPF.

RELATED: 10 Things Your Nails Can Tell You About Your Health

Areas of the body normally affected by psoriasis

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There are no special diagnostic tests for psoriasis. Instead, a psoriasis diagnosis is made by a dermatologist, who will examine the skin lesions visually. In some cases, psoriasis can resemble other types of skin conditions, like eczema, so doctors may want to confirm the results with a biopsy. That involves removing some of the skin and looking at the sample under a microscope, where psoriasis tends to appear thicker than eczema.

Doctors may also take a detailed record of your familys medical history: About one-third of people with psoriasis have a first-degree relative who also has the condition. Health care providers may also try to pinpoint psoriasis triggers by asking whether their patients have been under stress lately or are taking a new medication.

Theres no one-size-fits-all psoriasis treatment, and the medications that work for some people may not work for others. The goal, however, is the same for everyone: to find psoriasis medications that can reduce or eliminate psoriasis symptoms. Here are some of the most commonly prescribed therapies.

Topical medications. A first-line form of therapy for mild to moderate conditions, topicals (in psoriasis cream, gel, and ointment forms) are applied directly to the skin in the hopes of reducing inflammation and slowing down skin cell growth. Some are available over-the-counter, like products with salicylic acid and coal tar as active ingredients, while others, like calcipotriene (a form of vitamin D3) and tazarotene (a vitamin A derivative known as a retinoid) are available by prescription. There are also special psoriasis shampoos that can help clear up scalp psoriasis; many contain coal tar and salicylic acid.

Phototherapy. Also called light therapy, phototherapy exposes a persons skin to ultraviolet light, which is thought to kill the immune cells contributing to psoriasis. Phototherapy can be administered in the form of UVB rays, a combination of UVA and UVB, or UVA rays alongside an oral or topical medication called psoralen (a treatment called PUVA). The catch: These treatments have to be done in a doctors office, a psoriasis clinic, or with a specialized phototherapy unit and usually require several visits, which can become expensive. Because indoor tanning increases the risk of skin cancer (especially melanoma), its not considered a safe substitute for phototherapy under medical supervision.

Systemic medications. If topical medications and phototherapy dont work, doctors may recommend taking systemics, or prescription drugs that affect the entire body. These meds can be taken orally or via an injection, and include cyclosporine (which suppresses immune system activity and slows skin cell growth), acitretin (an oral retinoid, or form of vitamin A, that slows down the speed at which skin cells grow and shed), and methotrexate (a medication that was originally used as a cancer treatment, but can also slow down the growth of skin cells).

Biologic drugs. Biologics contain human or animal proteins and can block certain immune cells that are involved in psoriasis. Theyre usually recommended for people with moderate to severe psoriasis and are administered via an injection or IV infusion. There are currently three types of biologics that can help treat psoriasis, all of which block immune system chemical messengers that promote inflammation called cytokines. The three types of biologics block the cytokines tumor necrosis factor alpha (TNF-alpha), interleukin 12, interleukin 23, and interleukin 17-A (IL-12, IL-23, and IL-17A, respectively).

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Alternative and complementary therapies. Some alternative therapiesincluding acupuncture, massage, and Reikimight help relieve certain psoriasis symptoms, like pain. They may also help control stress, a common psoriasis trigger. Other stress-relievers include meditation, mindfulness, exercise, yoga, and Tai Chi. Always talk to your doctor before beginning any alternative psoriasis treatments.

There is currently no cure for psoriasis. As a chronic autoimmune disease, most people with psoriasis will always have it. But it is possible to treat the condition. In fact, the right medications and therapies can reduce symptoms and even clear up the skin entirely in some people.

More psoriasis treatments may be available in the future. Researchers are currently trying to uncover what causes the lesions on a cellular level and how to prevent flare-ups caused by the immune system.

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For the millions of Americans who have psoriasis, the skin condition can pose many challenges. Not only can the pain and itching interfere with their ability to sleep or work, but research shows that many people with psoriasis feel unattractive; worse, if they feel self-conscious, they may withdraw from their friends and family and become isolated.

People with psoriasis are also twice as likely to be depressed as those who dont have the skin condition, according to the NPF, and they can also be more likely to have suicidal thoughts. If youre feeling a loss of energy, lack of interest in once-enjoyable activities, or an inability to focus, talk to your doctor about whether you may have depression or should see a mental health specialist.

An estimated 30% of people with psoriasis will also develop psoriatic arthritis, a disease which causes joint pain, stiffness, and swelling. Having psoriasis may also make people more likely to develop cardiovascular disease, obesity, and diabetes, according to the NPF.

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There are many ways that people living with psoriasis can manage the condition. This includes avoiding tobacco, alcohol, and unhealthy foods. Although there is no psoriasis diet, per se, eating healthy meals may help you feel better. You should also keep tabs on whether your joints feel stiff or sore or whether your nails are pitting or turning yellowtwo possible signs of psoriatic arthritis. Recognizing these symptomsand getting treatmentcan help prevent further damage to the joints.

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Anyone can develop psoriasiseven the most beautiful people on the planet. And as people who are paid to look flawless, many celebrities with psoriasis say that the skin condition delivers a serious blow to their self-esteem and fear that it can interfere with their careers.

In 2011, Kim Kardashian revealed her psoriasis diagnosis on an episode of Keeping Up With the Kardashians. Although her mother, Kris Jenner, was diagnosed with psoriasis at the age of 30, Kim was surprised to learn that she had the skin condition too. My career is doing ad campaigns and swimsuit photo shoots, she said in the episode. People dont understand the pressure on me to look perfect. Imagine what the tabloids would do to me if they saw all these spots.

Model and actress Cara Delevingne also has psoriasis, which she struggled to manage while runway modeling. She told Londons The Times in an interview that people would paint her body with foundation to cover up the patches. It was every single show, she said. People would put on gloves and not want to touch me.

Other models also struggle with psoriasis, like CariDee English, who won Americas Next Top Model in 2006. Partly in response to the hurtful tabloid headlines that called out the lesions on her legs, she posted before-and-after photos of one of her flare-ups, saying, I knew I didnt want anyone capturing my psoriasis in a way that wasnt empowering.

Other celebs who have psoriasis include golfer Phil Michelson, country singer LeAnn Rimes, and pop star Cyndi Lauper.

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