Study provides evidence why autism is more common in males

Findings suggest that more extreme genetic alterations are required in the female brain to produce symptoms of ASD or neurodevelopmental disorders.

The underlying reasons are not exactly clear, but males pose a greater risk for autism and other neurodevelopmental disorders.

On February 27 Cell Press published a study in the American Journal of Human Genetics supporting the theory of “female protective model,” indicating females require more extreme genetic mutations to push them over the diagnostic threshold for neurodevelopmental disorders than males.

Study author Sébastien Jacquemont of the University Hospital of Lausanne says, “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” The prevalence of neurodevelopmental disorders shows a gender bias for ASD, attention deficit hyperactivity disorder and intellectual disability. “The study suggests that there is a different level of robustness in brain development, and females seem to have a clear advantage,” says Jacquemont.

 It has been suggested by some researchers that a social bias in males increases the likelihood of diagnosis. Others have proposed that there are sex-based differences in genetic susceptibility. In past studies investigating biological explanations inconclusive results have been produced for the gender bias.

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

They found greater number of harmful CNVs in females diagnosed with a neurodevelopmental disorder or ASD than did males diagnosed with the same disorder. Moreover, there was a greater number of harmful SNVs in females diagnosed with ASD than there were in males with ASD. These findings suggest that more extreme genetic alterations are required in the female brain than is required in the male brain to produce symptoms of ASD or neurodevelopmental disorders. Suggesting that the burden difference is genome wide, the focus has been taken off the X chromosome for the genetic basis of the gender bias.

“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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