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. Most evidence suggests the vaccine hypotheses are
biologically implausible and lacking 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 diagnosed with autism has increased dramatically since the 1980s, partly due to changes in
diagnostic practice; the question of whether actual prevalence has increased is unresolved.
Parents usually notice signs in the first two years of their child's life. The signs usually develop gradually,
but some autistic children first develop more normally and then regress. Although early behavioral or cognitive
intervention can help autistic children gain self-care, social, and communication skills, there is no known cure.
Not many children with autism live independently after reaching adulthood, though some become successful. An
autistic culture has developed, with some individuals seeking a cure and others believing autism should be
tolerated as a difference and not treated as a disorder.