Researchers have found that small, common gene variations can add up to substantially increase risk for autism spectrum disorders (ASD). Their study, published this week in Molecular Autism, found the cumulative effects of these small gene changes are a major source of autism risk.
“This could explain why, while the parents might each not show any symptoms, their children receive enough of the risk versions to be affected,” explains study co-author Bernie Devlin, Ph.D., of the University of Pittsburgh. "Each of the common variations involved in ASD has little effect on its own. However our results show that they add up."
The findings also highlight the many different genetic combinations that can predispose individuals to autism, says Andy Shih, Ph.D., Autism Speaks senior vice president for scientific affairs. “This may help us better understand the genetic components of autism and possibly the environmental factors that interact with them,” he adds.
In all, the researchers analyzed one million common variations in the genomes of just over 2,000 families affected by autism. In families with only one affected child, 40 percent of autism risk appeared to be inherited. In families with more than one affected child, the role of inherited risk increased to more than 60 percent.
The findings are so important because they begin to clarify the role of small, common genetic variations, Dr. Shih explains. The complex causes of ASD involve both inherited and environmental influences. In recent years, the strong effect of certain rare autism genes has become clear. In and of themselves, these rare mutations appear sufficient to cause autism.
By contrast, scientists have yet to fully understand the role of more common autism risk genes. Many involve tiny changes in a gene’s DNA sequence and increase risk only slightly. The new findings suggest that, cumulatively, they form a major source of increased risk.
The analysis was made possible by two large collections of genetic information from families affected by ASD. The first is the Autism Genome Project (AGP). The AGP provides qualified researchers with anonymous genetic information from thousands of families with one or more affected children. Autism Speaks supports the AGP through both research grants and anonymous genetic information from families who participate in its Autism Genome Research Exchange. The second autism database was the Simons Simplex Collection. It provides genetic information from families with only one child and neither parent affected by autism.