A group of conditions involving serious impairment in several areas of development, including physical, behavioral, cognitive, social, and language development.

The incidence of pervasive development disorders (PDDs) in the general population is estimated at 1%. These disorders are thought to be genetically based, and there is no evidence linking them to environmental factors. Many children who are diagnosed with PDDs today would have been labeled psychotic or schizophrenic in the past. The most serious form of pervasive developmental disorder is autism, a congenital condition characterized by severely impaired social interaction, communication, and abstract thought, and often manifested by stereotyped and repetitive behavior patterns.

In addition to autism, several other conditions are considered pervasive developmental disorders by the American Psychiatric Association. Rett's disorder is characterized by physical, mental, and social impairment that appears between the ages of five months and four years in children...