Another 34 genes have been linked with autism spectrum disorder, according to a presentation yesterday (October 16) at the American Society of Human Genetics annual meeting in San Diego.

Harvard Medical School graduate student Jack Kosmicki and his colleagues studied exome sequences of 37,269 individuals with autism and pinpointed 99 genes that could play a role in causing the disorder, 65 of which had previously been identified. The new result builds on work from the last decade and provides a “very accurate list” of genes that Kosmicki and his colleagues are confident play a role in the disorder.

“Autism is a common condition, but we don’t know its cause. We think it is predominantly genetic, so if we can understand the underlying biology, we can develop a therapy for the symptoms of the disorder,” Stephan Sanders, a geneticist and pediatrician at the University of California,...

One challenge with developing therapies is that symptoms of the disorder vary widely, especially in terms of intellectual abilities. “In autism, we have patients all across the IQ spectrum,” Sanders says. Adding genes to the list associated with autism has helped the researchers begin to tease apart which ones specifically are more strongly associated with autism alone (that is, kids with ASD who have typical intellectual performance and development) compared with those more strongly linked to intellectual disability and developmental delay. 

The team collected data on the intellectual abilities of about 80 percent of the individuals whose genetic samples were included in the study and also gathered previously published data on genetic mutations associated with intellectual disability and developmental delay. A meta-analysis of the results revealed that about half of the 99 ASD genes identified are more strongly associated with intellectual disability and developmental delay than with ASD, and the other half were more strongly related to ASD alone, while only a few were related to both ASD and intellectual disability and developmental delay.

In addition, the team found that patients with variants in the genes more strongly tied to intellectual disability and developmental delay walked 2.6 months later and had an 11.7-point lower IQ, on average, than patients with variants in ASD genes not tied to intellectual or developmental issues. Parsing the genes in such a way helps to explain why individuals with autism differ widely in their development and behavior.

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