That only one common variant came out of this large sample study indicates that "there probably are many more that contribute to autism, but none have large effects," says Dan Arking, Ph.D., assistant professor of medicine at Hopkins' McKusick-Nathans Institute of Genetic Medicine. "Alternatively, there may be numerous rare gene-variant containing genes." Identifying these will require even larger collaborative studies that are currently under way, he adds.

The identification of semaphorin 5A, and seven additional likely ” but not yet proven ” genes involved in nervous system development, cell structure and other cell functions, only was possible through an extensive collaborative effort that included inpatient samples from the Autism Consortium in Montreal, the Autism Genome Project and additional samples from Finland and Iran.

"These discoveries are an important step forward, but just one of many that are needed to fully dissect the complex genetics of this disorder," says Mark Daly, Ph.D., a senior associate member at the Broad Institute of Harvard and MIT and an associate professor at the Center for Human Genetic Research at Massachusetts General Hospital. "The genomic regions we've identified help shed additional light on the biology of autism and point to areas that should be prioritized for further study."

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