Special Needs & Autism

The epidemiology of autism is the study of factors affecting autism spectrum disorders (ASD). more...

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Most recent reviews estimate a prevalence of one to two cases per 1,000 people for autism, and about six per 1,000 for ASD; because of inadequate data, these numbers may underestimate ASD's true prevalence. ASD averages a 4.3:1 male-to-female ratio. The number of children known to have autism has increased dramatically since the 1980s, at least partly due to changes in diagnostic practice; the question of whether actual prevalence has increased is unresolved, and as-yet-unidentified contributing environmental risk factors cannot be ruled out. The risk of autism is associated with several prenatal and perinatal factors, including advanced parental age and low birth weight. ASD is associated with several genetic disorders and with epilepsy, and autism is associated with mental retardation.

Autism and its causes

Further information: Causes of autism

Autism is a complex neurodevelopmental disorder. Many causes have been proposed, but its theory of causation is still incomplete. Autism is largely inherited, although the genetics of autism are complex and it is generally unclear which genes are responsible. Although a link between autism and environmental exposures is plausible, little evidence exists to support associations with specific environmental exposures. In rare cases, autism is strongly associated with agents that cause birth defects. Other proposed causes, such as childhood vaccines, are controversial and the vaccine hypotheses lack convincing scientific evidence.

Frequency

Although incidence rates measure autism risk directly, most epidemiological studies report other frequency measures, typically point or period prevalence, or sometimes cumulative incidence. Attention is focused mostly on whether prevalence is increasing with time.

Incidence and prevalence

Epidemiology defines several measures of the frequency of occurrence of a disease or condition:

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