What role does inheritance play?

Recent studies strongly suggest that some people have a genetic predisposition to autism. In families with one autistic child, the risk of having a second child with the disorder is approximately 5 percent, or one in 20. This is greater than the risk for the general population.

Researchers are looking for clues about which genes contribute to this increased susceptibility. In some cases, parents and other relatives of an autistic child show mild impairments in social and communicative skills or engage in repetitive behaviors.

Evidence also suggests that some emotional disorders, such as manic depression, occur more frequently than average in the families of people with autism.

Autism & Genes A National Institute of Child Health and Human Development Report