Autism is a disorder of neural development characterised by impaired social interaction and communication, and by restricted and repetitive behavior. 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.

The prevalence of autism is about 1–2 per 1,000 people worldwide; however, the centres for Disease Control and Prevention (CDC) reports approximately 9 per 1,000 children in the United States are diagnosed with ASD.[2][3] 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.