A child whose development is delayed learns those skills, but learns them at a slower rate. A child with autism, though, has very inconsistent development. Autism is diagnosed by the presence or absence of certain behaviors, characteristic symptoms and developmental delays early in life, usually prior to thirty months of age. This information is taken both by examination and from the child's known history. Autism and its behavioral symptoms occur in approximately one per 500 births.
Autism is four times more common in boys than in girls.
It has been found throughout the world, in families of all racial, ethnic and social backgrounds. Although it is not known what causes autism, it is believed that anything that can produce structural or functional damage in the central nervous system can also produce the syndrome of autism. Certain viruses and genetic conditions are thought to be associated with autism. Since science is unable to determine what causes autism, it cannot medically correct the problems in the child's brain. There is more misinformation about autism than any other disorder.