Autism has a strong genetic basis — genes play a big role in its occurrence. Studies of twins have led researchers to estimate the Heritability of autism to be more than 90%.

New research from Carnegie Mellon University suggests this genetic risk comes not from rare variations or sudden mutations but from changes in our DNA that are more common.

The study found that approximately 52% of autism could be traced to common genes and rarely inherited variations, with sudden mutations accounting for only 2.6%. The research, focusing on about 3,000 subjects, is the largest of its kind and suggests that the inherited risk for autism outweighs environmental risks.

…[F]or many families, the interplay between common and spontaneous genetic factors could be the underlying genetic architecture of the disorder.

“From this study, we can see that genetics plays a major role in the development of autism compared to environmental risk factors, making autism more like height than we thought — many small risk factors add up, each pushing a person further out on the spectrum,” Kathryn Roeder, professor of statistics and computational biology at Carnegie Mellon and lead author of the study, said in a statement.

“These findings could not have happened without statistics, and now we must build off of what we learned and use statistical approaches to determine where to put future resources, and decide what is the most beneficial direction to pursue to further pinpoint what causes autism.”

The genetics of autism is coming of age. New statistical methods allowed researchers to decipher the heritability of autism. They were able to compare their results with a similar study that included twins, cousins, and useful factors.

“Thanks to the boost in statistical power that comes with ample sample size, autism geneticists can now see the forest for the trees,” Thomas R. Insel, director of the National Institute of Mental Health (NIMH) said. “Knowing the nature of the genetic risk will help focus the search for clues to the molecular roots of the disorder.”

Scientific efforts are now zeroing in on very specific genetic mutations that were detected in the study group.

“Within a given family, the mutations could be a critical determinant that leads to the manifestation of ASD in a particular family member,” Joseph Buxbaum, first author and professor of psychiatry, neuroscience, genetics and genomic sciences at the Icahn School of Medicine at Mount Sinai (ISMMS), said.

“The family may have common variation that puts it at risk, but if there is also a ‘de novo’ mutation on top of that, it could push an individual over the edge. So for many families, the interplay between common and spontaneous genetic factors could be the underlying genetic architecture of the disorder.”

So far, studies have not been large enough to reveal common genetic variations that are linked to autism. The research group at Carnegie Mellon hopes to develop a model that predicts risk based on all of these various factors.

The study is published in Nature Genetics.