As of 2015, the scientific consensus is that autism spectrum disorders may be inherited, but scientists have not yet found the exact genes responsible, according to WebMD. Autism seems to run in families; however, there may be other non-hereditary causes of the disorder.
The prevalence of autism spectrum disorder in children who have a sibling with the disorder is much higher than the prevalence in the general population. However, it is lower than the prevalence of most disorders caused by a single inherited gene, states PubMed. This suggests that autism spectrum disorders are inherited, but that multiple genes or a combination of genes and environment are responsible for the development of the disorder and the its severity.