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.[4] In rare cases, autism is strongly associated with agents that cause birth defects.[5] Controversies surround other proposed environmental causes, such as heavy metals, pesticides or childhood vaccines;[6] the vaccine hypotheses are biologically implausible and lacking convincing scientific evidence.[7] The prevalence of autism is about 1¨C2 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.[8]

Parents usually notice signs in the first two years of their child's life.[9] The signs usually develop gradually, but some autistic children first develop more normally and then regress.[10] Although early behavioral or cognitive intervention can help autistic children gain self-care, social, and communication skills, there is no known cure.[9] Not many children with autism live independently after reaching adulthood, though some become successful.[11] 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.[12]