Autism is a pervasive developmental disorder, with abnormal behaviour manifestation occurring between 2.5 to 3 years. Autism is a disorder of neural development characterized by impaired social interaction, verbal and non-verbal communication, and by restricted and repetitive behaviour. The diagnostic criteria require that symptoms become apparent before a child is three years old. 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. 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.
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. In rare cases, autism is strongly associated with agents that cause birth defects. Controversies surround other proposed environmental causes, such as heavy metals, pesticides or childhood vaccines; the vaccine hypotheses are biologically implausible and lack convincing scientific evidence. The prevalence of autism is about 1–2 per 1,000 people worldwide, and it occurs about four times more often in boys than girls. The number of people diagnosed with autism has been increasing dramatically since the 1980s, partly due to changes in diagnostic practice and government-subsidized financial incentives for named diagnoses; the question of whether actual prevalence has increased is unresolved.
- Impairment of social reciprocal behaviour.
- Abnormal or impaired speech and language development.
- Demand for sameness.
- Often associated with mental retardation.
- Restricted repertoire of interests and activities.