a developmental disorder that affects physical, social, and language skills. The syndrome usually appears before three years of age, although the earliest signs are quite subtle.

Autistic children (childhood disease and disorder) appear indifferent or averse to affection and physical contact, although attachment to parents or certain adults often develops later. Speech develops slowly and abnormally (it is often atonal and arrhythmic) or not at all. It may be characterized by meaningless, noncontextual echolalia (constant repetition of what is said by others) or the replacement of speech by strange mechanical sounds. There may be abnormal reaction to sound, no reaction to pain, or no recognition of genuine danger, yet autistic children are extremely sensitive. Usually the syndrome is accompanied by an obsessive desire to prevent environmental change. Frequently there are also rhythmic body movements, such as rocking or hand-clapping. About 25 percent of autistic children develop seizures by late adolescence.

Estimates of the prevalence of autism range from 10 to 20 per 10,000 children; some 15 to 20 percent are able to become socially and vocationally independent. The disorder is about four times more common in males.

Autism is still incompletely understood. Abnormalities of the brain (particularly in the cerebellum, brain stem, and limbic system) are likely to have occurred during early development. Genetic or environmental influences, a deficiency of large neurons called Purkinje cells in the cerebellum, or an excess of the neurotransmitter serotonin may also cause autism. There is no cure for autism; behavioral or drug therapy may improve some symptoms. People with the condition have a normal life expectancy.