They seem not to hear certain sounds or may overreact to other sounds. Some appear to have insensitivity to pain and very low sense of fear. There is still no known cause. Some believe there is a physical problem affecting the brain areas that process language. Others think that there could be a chemical imbalance in the brain.
Genetic factors are also a possibility.
Autistic behaviors occur in 15 out of every 10,000 individuals. Three out of four are males. It is one of the four major developmental disabilities. Autism does not discriminate. It affects all races, nationalities, and social classes.