What are the known causes of autism?
No one knows exactly what causes autism, but scientists think that both genetic and environmental factors may play a role. Family studies have shed the most light on the genetic contribution to autism. Studies of twins have shown that in identical twins there is about a 75% rate of both twins having autism, while in non-identical twins this occurs about 3% of the time. The risk of autism in siblings ranges from 2 to 6 percent. And in families with autism, there are often other developmental problems as well, such as language delays or learning disabilities. The inheritance pattern is complex and suggests that a number of genes are involved. Autism also tends to occur more frequently than expected among individuals who have certain other medical conditions, including Fragile X syndrome, tuberous sclerosis, congenital rubella syndrome, and untreated phenylketonuria (PKU). Some harmful substances ingested during pregnancy also have been associated with an increased risk of autism, specifi
