Autism spectrum disorder includes conditions that were previously considered separate — autism, Asperger’s syndrome, childhood disintegrative disorder and an unspecified form of pervasive developmental disorder.
Autism spectrum disorder begins in early childhood and eventually causes problems functioning in society — socially, in school and at work, for example. Often children show symptoms of autism within the first year. A small number of children appear to develop normally in the first year, and then go through a period of regression between 18 and 24 months of age when they develop autism symptoms. Each child with autism spectrum disorder is likely to have a unique pattern of behavior and level of severity — from low functioning to high functioning.