Autism is a disorder of neural development characterized by impaired social interaction and communication, and by restricted and repetitive behavior. Others also exhibit sensory processing deficits, as well as symptoms related to agression, attention, hyperactivity, and speech. These signs all begin before a child is three years old.[1] Autism affects information processing in the brain by altering how nerve cells and their synapses connect and organize; how this occurs is not well understood.[2] It is one of three recognized disorders in the autism spectrum (ASDs), the other two being Asperger syndrome, which lacks delays in cognitive development and language, and Pervasive Developmental Disorder-Not Otherwise Specified (commonly abbreviated as PDD-NOS), which is diagnosed when the full set of criteria for autism or Asperger syndrome are not met.[3]

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, or pesticides;[6] theories relating to childhood vaccines are biologically implausible and lack convincing scientific evidence.[7] 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.[8] According to the Center for Disease Control and Prevention in 2009, studies show that since 2006 autism has been diagnosed in 9.0 per 1,000 children in the United States.[9]

Parents usually notice signs in the first two years of their child's life.[10] The signs usually develop gradually, but some autistic children first develop more normally and then regress.[11] Although early behavioral or cognitive intervention can help autistic children gain self-care, social, and communication skills, there is no known cure.[10] Not many children with autism live independently after reaching adulthood, though some become successful.[12] An autistic culture has developed, with some individuals seeking a cure and others believing autism should be accepted as a difference and not treated as a disorder.[13]