Autism causes :

Autism has no single, known cause. Given the complexity of the disease, and the fact that symptoms and severity vary, there are probably many causes. Both genetics and environment may play a role.

• Genetic problems. Several genes appear to be involved in autism. Some may make a child more susceptible to the disorder. Others affect brain development or the way that brain cells communicate. Still others may determine the severity of symptoms. Each problem in genes may account for a small number of cases, but taken together, the influence of genes is likely substantial. Some genetic problems seem to be inherited, while others happen spontaneously.
• Environmental factors. Researchers are currently exploring whether such factors as viral infections, complications during pregnancy and air pollutants play a role in triggering autism.