Autism Risk Not Just Genetic

Although the risk of autism is partly inherited, environmental factors play a major role, according to a new study.

Using California state records, researchers at Stanford University found 192 sets of identical and fraternal twins in which at least one of the two was diagnosed with autism. They also screened the twins for the disorder. Statistical analysis showed that the twins had a 38 percent risk of developing autism based on genetics and a 58 percent risk based on the environment.

Environmental factors can cause autism, not just genetics.

These results, published online in the journal Archives of General Psychiatry, suggest that the environment plays a bigger part in autism than previously thought, said the scientists, including lead author Dr. Joachim Hallmayer, associate professor of psychiatry and behavioral science at Stanford.

Environmental factors that could contribute to autism risk include parental age, low birth weight, multiple births and infections during pregnancy.

The findings also suggest that fraternal twins have a higher risk of both having autism than realized before. Previously, researchers have focused more on that risk in identical twins.

This study was the largest twin study of autism using current diagnostic criteria.

Most autism-related research has focused on genetic causes, and this study shows that scientists need to look closely at environmental factors as well, researchers said.