I have had an interest in autism for a while, since I've known a couple of people with Aspergers, a form of autism. The other thing that has intrigued me is the controversy about vaccines and autism. So I recently did some reading about it.
Autism is a neurological disorder that is characterized by social and emotional impairments, communication problems, and strange, repetitive behavior. It's actually a wide range of impairments. Autistic people have different connections in their brains--their brains are not wired like everyone else's. There are several things that are thought to cause this, but research is ongoing because there aren't a lot of solid answers yet.
There are several possibilities that may cause autism. One that is pretty certain is genetics. It seems to arise from a spontaneous mutation. Two different genetic causes are Fragile X Syndrome and Rett Syndrome.
Chemicals in our environment may cause problems with the proteins in the brain, causing it to malfunction. A recent scientific article in April called for more research into 10 chemicals that are suspected of causing autism. Two of those chemicals were pesticides, and one was automotive exhaust. There have been studies done that linked smoking during pregnancy and Depakote, a drug that may be taken during pregnancy. A very recent study links psychoactive drugs and autism.
There was a study done in 1998 that linked vaccines and autism. But the study focused on only 12 children, and 10 of the 13 scientists withdrew their names from the interpretation of the results. Since then, there have been 12 studies done that have disproved the first study.