There is no theory of the cause of autism which everyone has found convincing. There may be multiple causes. Thus we will review some of the proposed causes.
Most researchers are absolutely convinced that the cause is biological rather than psychological.
Parents who do fit the description of the supposedly pathogenic parent almost invariably have normal, non-autistic children. With very few exceptions, the siblings of autistic children are normal. There is a consistent ratio of three or four boys to one girl. Virtually all cases of twins reported in the literature have been identical, with both twins afflicted. Autism can occur or be closely simulated in children with known organic brain damage.