autismstudy_sizedThe risk of having an Autism Spectrum Disorder (ASD) is greater for boys: 1 in 52 versus 1 in 252 for girls, according to the Centers for Disease Control. Researchers have long speculated that mutations in the X chromosome passed down by the father might be to blame, but a recent study published in the American Journal of Human Genetics reveals a new theory.

The researchers concluded that females actually carry more genetic mutations for ASD—but they’re “better at dealing with severe mutations and males are more at risk for having mutations result in disease. Researchers added that they believe it takes more to push females into a state of intellectual disability, because females have two X chromosomes (versus the one that boys have).

To conduct the study, Evan Eichler, a professor of genome science at the University of Washington School of Medicine in Seattle, teamed with a colleague, Sebastien Jacquemont, of University Hospital of Lausanne, Switzerland. The pair analyzed DNA samples from nearly 16,000 people with neurodevelopment disorders, and they also looked at additional samples from a separate group of 800 families affected by ASD.

The scientists discovered that while boys were more affected by ASD, the serious genetic mutations were more likely to be passed to children through their mother's DNA as opposed to their father's. And analyzing the group of 16,000 they discovered that female children had a larger number of genetic mutations known to be associated with neurodevelopment disorders than did male children. Even in the smaller 800 family group, the researchers saw that girls had both more major and a higher number of small mutations compared to the boys. Sixty percent of the severe genetic mutations came from the child's mother, with 40 percent