A pervasive developmental disorder, autism affects information processing in multiple ways. Many people with autism have difficulties with social interactions and communication, sensory deficits, and poor motor coordination. Autistic people often have restricted interests and engage in repetitive behaviors.
Because autism's symptoms vary greatly, it's said to exist on a spectrum, and is increasingly referred to as Autism Spectrum Disorder. (Asperger's is a condition often referred to as "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 males than females. 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 increasing the risk of direct genetic mutations or of factors that influence the expression of genes in he developing brain.
Reports implicating mercury-containing vaccines have proved baseless, although there is some evidence that environmental toxins may play a role. Some research suggests that autism reflects an "extreme male brain," because people with the condition often have an obsession with details and systematizing but are low on empathic ability. There is no cure for autism, although some symptoms may ease over the years.