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Newswise It takes more mutations to trigger autism in women than in men, which may explain why men are four times more likely to have the disorder, according to a study published 26 February in the American Journal of Human Genetics1.

The study found that women with autism or developmental delay tend to have more large disruptions in their genomes than do men with the disorder. Inherited mutations are also more likely to be passed down from unaffected mothers than from fathers.

Together, the results suggest that women are resistant to mutations that contribute to autism.

This strongly argues that females are protected from autism and developmental delay and require more mutational load, or more mutational hits that are severe, in order to push them over the threshold, says lead researcher Evan Eichler, professor of genome sciences at the University of Washington in Seattle. Males on the other hand are kind of the canary in the mineshaft, so to speak, and they are much less robust.

The findings bolster those from previous studies, but don't explain what confers protection against autism in women. The fact that autism is difficult to diagnose in girls may mean that studies enroll only those girls who are severely affected and who may therefore have the most mutations, researchers note.

The authors are geneticists, and the genetics is terrific, says David Skuse, professor of behavioral and brain sciences at University College London, who was not involved in the study. But the questions about ascertainment are not addressed adequately.

Genetic burden:

The new study draws from the Simons Simplex Collection (SSC), a database of families that have one child with autism and unaffected parents and siblings. (This project is funded by the Simons Foundation, SFARI.orgs parent organization.) In a 2011 study, researchers found that girls with autism in the SSC tend to have more large duplications or deletions of regions of the genome, called copy number variants (CNVs), than do boys with the disorder, although this disparity does not reach statistical significance2.

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Girls Protected From Autism, Study Suggests