Gene therapy is the insertion of genes into an individual's cells and tissues to treat a disease, and hereditary diseases in which a defective mutant allele is replaced with a functional one.

Although the technology is still in its infancy, it has been used with some success.

Antisense therapy is not strictly a form of gene therapy, but is a genetically-mediated therapy and is often considered together with other methods.

In most gene therapy studies, a "normal" gene is inserted into the genome to replace an "abnormal," disease-causing gene.

A carrier called a vector must be used to deliver the therapeutic gene to the patient's target cells.

Currently, the most common type of vectors are viruses that have been genetically altered to carry normal human DNA.

Viruses have evolved a way of encapsulating and delivering their genes to human cells in a pathogenic manner.

Scientists have tried to harness this ability by manipulating the viral genome to remove disease-causing genes and insert therapeutic ones. Target cells such as the patient's liver or lung cells are infected with the vector.

The vector then unloads its genetic material containing the therapeutic human gene into the target cell.

The generation of a functional protein product from the therapeutic gene restores the target cell to a normal state. In theory it is possible to transform either somatic cells (most cells of the body) or cells of the germline (such as sperm cells, ova, and their stem cell precursors).

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Gene therapy - Science Daily

For patients with choroideremia a rare form of progressive blindness there are no current treatment options that can help stop their visual degeneration. But now a new innovative procedure may be the key.

In a new study published in The Lancet, researchers used a novel gene therapy technique on choroideremia patients, which helped restore some of the sight they had already lost over the years. Gene therapy involves injecting patients with a vital gene that is either missing or defective in their genetic code.

Gene therapy is exciting; its a new type of medicine, lead author Robert MacLaren, a professor at the University of Oxford, told FoxNews.com. And what were doing is it on a very small scale, because were looking at a very straightforward gene to replace.

Caused by a mutation in the CHM gene on the X chromosome, choroideremia causes progressive blindness due to degeneration of the choroid, retinal pigment epithelium and retina. Patients with this disease can start their lives with perfect vision, but eventually start to experience problems with light sensitivity and peripheral vision as they age.

The condition, which affects 1 in every 50,000 people, ultimately leads to the death of the photoreceptor cells in the retina causing complete blindness in middle age.

Its like looking down through a telescope at a small central island of vision, MacLaren explained of the disorder. And by the time theyre in their 40s and 50s, they lose vision completely.

Because choroideremia is caused by a defect in a single gene, MacLaren believed that gene therapy could hold promise for patients with this form of progressive blindness. Additionally, because the cellular degeneration occurs so slowly, the researchers had a large window of opportunity in which they could test their treatment before complete visual loss occurred.

In order to fix the mutation found in choroideremia patients, MacLaren and his colleagues genetically altered an adeno-associated virus (AAV), so that it carried a corrective copy of the CHM gene.

The virus is a small biological organism, and its very good at getting into cells, MacLaren said. But rather than deliver the viruss DNA, weve taken out most of the viral DNA and instead put in the missing gene. So it releases the DNA into the nucleus its a single stranded DNA with the missing [CHM] gene.

The researchers injected their engineered virus into the retinas of six patients between the ages of 35 and 63, all of whom were experiencing different stages of choroideremia. Four of the patients still had good eyesight, though they had almost no peripheral vision, and the other two patients had already started to experience vision loss.

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Gene therapy treats blindness

62-year-old Jonathan Wyatt was diagnosed at age 20 with choroideremia, a rare genetic disorder that causes progressive blindness. In recent years, he was unable to read. He was one of six patients in the gene therapy trial.

Jonathan Wyatt was diagnosed at age 20 with choroideremia, a rare genetic disorder that causes progressive blindness

CBS News

People with the disease lack a gene that helps the eye make a protein needed for normal vision. When scientists injected a copy of that gene into the eye, the retinal cells started producing the protein. All six patients had improved vision and two, including Wyatt, had dramatic results.

Robert Maclaren of Oxford University led the study.

Rather than taking a pill or proteins or tablets, were actually correcting the disease at the genetic level, Maclaren said. In other words, genetically modifying the patients who have the problems to put the gene back thats missing.

"Well, this is a game changer because this is something that's been hypothesized and worked on for almost two decades, Schwartz told CBS News. The eye is the perfect organ into which gene therapy can begin to be successful because it's small, the amount of medication that needs to go into the eye is low, it's relatively safe.

One way this therapy could be useful in patients with macular degeneration is to eliminate the need for monthly injections of drugs into the eye. A single gene treatment could teach the eye to produce the medicine itself, but more testing is needed.

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Gene therapy has clear results for seeing-impaired

Two adults with a rare disease that causes gradual loss of eyesight had their vision improved after being treated with a new gene therapy, according to preliminary results from a new study.

The study involved six patients ages 35 to 63 with choroideremia, an inherited condition with no cure that causes vision problems early in life, and eventually leads to blindness. Patients have a mutation in a gene called CHM, which causes light-sensitive cells in the eye to slowly stop working.

The goal behind the new gene therapy is to use a safe virus to deliver a working copy of the gene to the right part of the eye to prevent the cells from degenerating. [7 Diseases You Can Learn About From a Genetic Test]

The new study was an early test of the therapy in which the researchers aimed to carry out the treatment without causing damage to the eye. (Patients must have an eye surgery so that the virus can be injected under the retina with a fine needle).

The result showed that the treatment did not cause harm, and in fact, improved vision in a few of the patients.

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Six months after the treatment, four patients recovered the visual acuity (clearness or acuteness of vision) that they had before the surgery, and developed increased sensitivity to light. And two patients had improvements in vision: They were able to read two to four more lines on a sight chart.

"We did not expect to see such dramatic improvements in visual acuity," study researcher Robert MacLaren, of the Nuffield Laboratory of Ophthalmology at the University of Oxford in the U.K., said in a statement. It is still too early to know if the improvements will last, but they have so far been maintained for as long as two years, MacLaren said.

The study is the first to test gene therapy in patients before they'd experienced significant thinning of the retinal cells, MacLaren said.

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Gene therapy improves vision for some with rare disease

By delivering gene therapies to patients before they go blind, doctors may be able to prevent the loss of many important light-detecting cells.

Light preserver: Robert MacLaren performs retinal surgery on a patient participating in a gene therapy experiment at the Oxford University Eye Hospital.

A new kind of gene therapy has reversed some vision loss in people born with a degenerative eye disease for which there is no existing treatment.

In a first for the field, the treatment can be given to some participants who still had 20/20 vision, albeit in a limited field of vision. By delivering gene therapy at an earlier stage, researchers hope to save more light-sensing cells in the retina.

We need to push gene therapy forward, to apply it before vision is gone, says Robert MacLaren, an ophthalmologist at the University of Oxford who led the study. When retinal damage gets to a certain point, its beyond repair.

MacLaren says earlier treatment could also be particularly important for conditions such as retinitis pigmentosa and age-related macular degeneration.

The surgical procedure employed put the precious remaining vision of patients in the trial at risk because it involved detaching delicate retina tissue in one of each participants eyes, but so far no problems have occurred since that surgery, the researchers report. Some participants report that theyre now able to detect more light, read more letters and numbers, and even see the stars at night. One patient, who before his treatment could not read any lines on an eye chart with his most affected eye, was able to read three lines with that eye following his treatment.

The condition addressed in the work is choroideremia, an eye disease that affects an estimated one in every 50,000 people. Because the gene that causes this disease is on the X chromosome, it primarily affects males. Starting in late childhood usually, the condition causes progressive narrowing or tunneling of vision and often ends in blindness. The condition gradually wipes out the light-detecting rods and cones in the retina.

The experimental treatment adds a working copy of the culpable gene to the retinal cells of patients born with a defective copy. The trial also involved an experimental way of delivering gene therapy to the eye. Each patients retina was first lifted, and the gene therapy was injected into the space created under the retina. MacLaren and colleagues report on the condition of six patients in a study published on Wednesday in the Lancet.

Other groups are also developing gene therapies for retinal diseases. This includes a group at Childrens Hospital of Philadelphia, which recently funded a new company to continue human trials of a treatment for Lebers Congenital Amaurosis, another inherited form of retinal degeneration (see New Gene Therapy Company Launches).

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Gene Therapy Tested as a Way to Stop Blindness

Thursday 16 January 2014 19.26

Pioneering gene therapy has restored vision to two men with a rare inherited eye disease who were told to expect to go blind.

Scientists hope early intervention with the surgical treatment will halt progression of the devastating disorder, choroideremia, before patients are robbed of their sight.

It is the first time gene therapy has successfully been applied to the light-sensitive photoreceptors of the retina, the digital camera at the back of the eye.

Preliminary results from the first six patients taking part in a Phase One trial surprised and delighted the Oxford University team.

Although the trial was only designed to test safety and dosages, two men with relatively advanced disease experienced dramatic improvements to their eyesight.

The researchers are now planning a larger Phase II trial that will focus on the therapy's effectiveness.

Professor Robert MacLaren, who led the gene therapy operations at Oxford Eye Hospital, said: "We're absolutely delighted with the results so far.

"It is still too early to know if the gene therapy treatment will last indefinitely, but we can say that the vision improvements have been maintained for as long as we have been following up the patients, which is two years in one case.

"In truth, we did not expect to see such dramatic improvements in visual acuity and so we contacted both patients' home opticians to get current and historical data on their vision in former years, long before the gene therapy trial started.

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Gene therapy breakthrough in blindness research