Boys are four times more likely than girls to have autism, and two studies hint at why: girls with the disorder tend to have many more genetic mutations than boys, suggesting that girls undergo greater genomic change before showing autistic behaviour.

Groups led by Michael Wigler at Cold Spring Harbor Laboratory in New York and Matthew State at Yale University in New Haven, Connecticut, conducted the most comprehensive search yet for spontaneous duplications or deletions of stretches of DNA that may be associated with autism spectrum disorders. In analysing the genomes of more than 1,000 people — some with autism, some unaffected family members — the teams found at least 130 sites in the genome where spontaneous duplications or deletions might contribute to autism risk.

State's team found that duplication of a region on chromosome 7 is associated with autism. Autism is marked by antisocial behaviour, and deletion of the same region is linked to Williams–Beuren syndrome, a condition that involves hypersocial behaviour.

In a third study, Dennis Vitkup at Columbia University in New York and his colleagues, in collaboration with Wigler, analysed relationships between the mutated genes uncovered by Wigler's genetics study that were likely to be involved in brain function. Many clustered into a large network that regulates the creation and activity of connections between nerve cells.

Neuron 70, 863–885 (2011); Neuron 70, 886–897 (2011); Neuron 70, 898–907(2011)