A pervasive developmental disorder, autism affects information processing in multiple ways. Many people with autism have difficulties with social interaction and communication, sensory deficits, and poor motor coordination. People with autism often have restricted interests and engage in repetitive behaviors. Because autism's symptoms vary greatly, the condition is said to exist on a spectrum, referred to as Autism Spectrum Disorder. (Asperger's syndrome is a condition that is considered to be "high functioning" autism.) Some people with autism have low intelligence while others are quite intelligent.
Autism usually manifests by age two. It affects far more men than women, although women are often overlooked and misdiagnosed. The frequency of diagnosis has surged over the past 20 years; it is not clear whether the incidence is truly increasing, whether experts are more alert to it, or whether the diagnosis has shifted to include lesser degrees of impairment. No one knows for sure what causes autism, but numerous studies link it to advanced maternal and/or paternal age at conception, which increases the risk of direct genetic mutations or factors that influence the expression of genes in the developing brain.
Some research suggests that autism reflects an "extreme male brain," because people with the condition often have in extreme form a number of traits associated with masculinity, including obsession with details and systematizing, and low empathic ability. Reports implicating mercury-containing vaccines have proved baseless, although there is some evidence that environmental toxins may play a role. There is no cure for autism, but some symptoms may ease over the years.