And researchers say they're on their way to discovering as many as 1,000 genes overall that may contribute to the disorder.
An estimated one in 68 American children has an autism spectrum disorder, according to the Centers for Disease Control and Prevention.
Before this research, scientists had identified fewer than a dozen genes apparently linked to autism risk.
The discoveries could lead to tools providing more accurate diagnoses and new directions for therapies.
The research results are published in the online issue of the journal Nature.