Daily Archives: February 27, 2014

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When it comes to developmental disorders of the brain, men and women are not created equal.

Decades of research have shown that males are at far greater risk for neurodevelopmental disorders such as autism spectrum disorder (ASD) than females. Boys, on average, are five times more likely to have autismthan girls.What causes this disparity has largely remained unknown.

Now scientists haveuncovered compelling genetic evidence to explain why the biological scales arent balanced.

According to a team of geneticists in the U.S. and Switzerland,it all boils down to whats called the female protective model. This suggests that girls have a higher tolerance for harmful genetic mutations and therefore require a larger number ofthem than boys to reach the diagnostic threshold of a developmental disorder. With identical genetic mutations, then, a boy could show symptoms of ASD while a girl could show none.

But because the female mutation threshold is higher, when girls are diagnosed with ASD, they tend to fall on the more severe end of the spectrum.

Researchers believe the same dynamic could explain why more boys are diagnosed withADHD, intellectual disabilities and schizophrenia. The findings were published Thursday in the American Journal of Human Genetics.

Geneticists analyzed DNA samples from 16,000 boys and girls with neurodevelopmental disorders.They found that, on average, females diagnosed with ASD had 1.3 to 3 times more harmful genetic alterations than males diagnosed with the disorder.

The findings suggest that as the male brain develops, smaller and more subtle genetic changes can trigger autism spectrum disorders. Female brains require a greater number or severity of mutations before showing symptoms, so their symptoms tend to be worse.

Theres no application in terms of treatment, said study author Sbastien Jacquemont of University Hospital of Lausanne in Switzerland, but it does help understand the inheritance dynamics in families.

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Genetics May Explain Why Autism Is More Common in Boys

By Dennis Thompson HealthDay Reporter

TUESDAY, Feb. 25, 2014 (HealthDay News) -- U.S. Food and Drug Administration hearings opened Tuesday on a controversial fertilization technique that uses the DNA from three people -- two women and one man -- with the goal of preventing inherited genetic diseases.

The technique involves the unfertilized eggs, or "oocytes," from two females. Parts of each egg are combined to weed out inherited genetic disorders contained in one woman's DNA, and the resulting healthy egg is then fertilized using a male's sperm.

The FDA's two-day hearing is meant to provide a forum for discussing how this technique might be tested in human clinical trials.

But the discussion is expected to veer into the ethics of manipulating human genetics to produce "perfect" babies.

"The potential benefits are huge, but the potential harms are also huge," said Dr. Michelle Huckaby Lewis, a faculty member at the Johns Hopkins Berman Institute of Bioethics and the Genetics and Public Policy Center, in Washington, D.C.

The procedure could have unintended health consequences both for newborns and for future generations, as the genetic tinkering reverberates through time, Lewis said.

In addition, she said, the technique raises troubling questions of parental rights and family structure.

"When you use a technology in a new way like this, it really challenges our notions of what it means to be a parent and what it means to be a family," Lewis said.

The hearing was prompted by the work of Shoukhrat Mitalipov, an associate scientist at Oregon Health & Science University (OHSU).

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FDA Explores '3-Person' Embryo Fertilization

PUBLIC RELEASE DATE:

27-Feb-2014

Contact: Mary Beth O'Leary moleary@cell.com 617-397-2802 Cell Press

Males are at greater risk for neurodevelopmental disorders, such as autism spectrum disorder (ASD), than females, but the underlying reasons have been unclear. A large cohort study published by Cell Press on February 27th in the American Journal of Human Genetics provides compelling evidence in support of the "female protective model," which proposes that females require more extreme genetic mutations than do males to push them over the diagnostic threshold for neurodevelopmental disorders.

"This is the first study that convincingly demonstrates a difference at the molecular level between boys and girls referred to the clinic for a developmental disability," says study author Sbastien Jacquemont of the University Hospital of Lausanne. "The study suggests that there is a different level of robustness in brain development, and females seem to have a clear advantage."

A gender bias in the prevalence of neurodevelopmental disorders has been reported for ASD, intellectual disability, and attention deficit hyperactivity disorder. Some researchers have suggested that there is a social bias that increases the likelihood of diagnosis in males, whereas others have proposed that there are sex-based differences in genetic susceptibility. However, past studies investigating biological explanations for the gender bias have produced inconclusive results.

To examine this question, Jacquemont teamed up with Evan Eichler of the University of Washington School of Medicine to analyze DNA samples and sequencing data sets of one cohort consisting of nearly 16,000 individuals with neurodevelopmental disorders and another cohort consisting of about 800 families affected by ASD. The researchers analyzed both copy-number variants (CNVs)individual variations in the number of copies of a particular geneand single-nucleotide variants (SNVs)DNA sequence variations affecting a single nucleotide.

They found that females diagnosed with a neurodevelopmental disorder or ASD had a greater number of harmful CNVs than did males diagnosed with the same disorder. Moreover, females diagnosed with ASD had a greater number of harmful SNVs than did males with ASD. These findings suggest that the female brain requires more extreme genetic alterations than does the male brain to produce symptoms of ASD or neurodevelopmental disorders. The results also take the focus off the X chromosome for the genetic basis of the gender bias, suggesting that the burden difference is genome wide.

"Overall, females function a lot better than males with a similar mutation affecting brain development," Jacquemont says. "Our findings may lead to the development of more sensitive, gender-specific approaches for the diagnostic screening of neurodevelopmental disorders."

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Study uncovers why autism is more common in males