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Autism is a disorder of neural development that is characterized by impaired social interaction and...

Autism is a disorder of neural development that is characterized by impaired social interaction and communication, and by restricted and repetitive behavior. These signs all begin before a child is three years old. Autism involves many parts of the brain; how this occurs is not well understood. The two other autism spectrum disorders (ASD) are Asperger syndrome, which lacks delays in cognitive development and language, and PDD-NOS, diagnosed when full criteria for the other two disorders are not met. Autism has a strong genetic basis, although the genetics of autism are complex and it is unclear whether ASD is explained more by rare mutations, or by rare combinations of common genetic variants. In rare cases, autism is strongly associated with agents that cause birth defects. Controversies surround other proposed environmental causes, such as heavy metals, pesticides or childhood vaccines; the vaccine hypotheses are biologically implausible and lack convincing scientific evidence. The prevalence of autism is about 1–2 per 1,000 people; the prevalence of ASD is about 6 per 1,000, with about four times as many males as females. The number of people known to have autism has increased