Is Autism Genetic?

A new study looking at autism in 5 countries found that 80 percent of autism risk can be traced to inherited genes rather than environmental factors and random mutations.

The study, published July 18 in JAMA Psychiatry, analyzed data of nearly 2 million people across Denmark, Finland, Sweden, Israel, and Western Australia. It is the largest family-based genetic autism study to date, including children with autism, their siblings and cousins, as well as parents and their siblings.

“We expanded on previous results by including more family members and data from countries that vary widely in their autism health systems,” said Joseph Buxbaum, M.D., one of the study authors and professor of psychiatry at the Icahn School of Medicine at Mt. Sinai Medical Center. “We found that the strongest contributors to risk of autism are from inherited genes. Spontaneous genetic changes and other factors that we could not estimate are additional contributors to risk of autism.”

In addition, the study found very little or no risk resulting from maternal effects – such as chronic health conditions that are consistent across all of a woman’s pregnancies. But for maternal factors that might occur in only one pregnancy, the study’s analysis can’t separate out those risks.

While the study’s authors concluded that maternal effects create no risk for autism, researchers who study these effects say this is a complicated issue.

“The maternal effects aspect of the paper is a clever analytic approach. However, it is based on relatively small numbers of maternally linked cousin pairs with autism, and thus shouldn’t be taken as a definitive answer. Any interaction between inherited gene effects and environments are difficult to model in this approach,” said Daniele Fallin, Ph.D., an epidemiologist and chair of the Department of Mental Health at Johns Hopkins University’s Bloomberg School of Public Health. “While the results confirm the very important role of inherited genes in autism risk, it is a mistake to conclude that they rule out an important role for environmental risk or maternal effects.”

The study also showed the wide range in heritability data that results from each country’s culture around autism. In Western Australia, the data was on the lower end, while most of the Nordic countries reported higher heritability. If a country tends to diagnose autism less frequently, perhaps due to cultural differences or how and when providers screen for autism, the heritability is likely also to show up as a lower number.

“It is not easy to estimate the contribution of random genetic variation from this analysis, but understanding the power of genetic influences is critical to leading us toward personalized treatments and solutions in the future,” said Autism Speaks Chief Science Officer Thomas Frazier, Ph.D. “We encourage everyone with an autism diagnosis to speak with their provider about genetic testing and participate in genetics research when they can.”