Epidemiology of autism

The epidemiology of autism is the study of the incidence and distribution of autism spectrum disorders (ASD). A 2012 review of global prevalence estimates of autism spectrum disorders found a median of 62 cases per 10,000 people. There is a lack of evidence from low- and middle-income countries though.

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; it is unclear whether prevalence has actually increased; and as-yet-unidentified environmental risk factors cannot be ruled out. The risk of autism is associated with several prenatal factors, including advanced paternal age and diabetes in the mother during pregnancy. ASD is associated with several genetic disorders and with epilepsy.

Autism is a complex neurodevelopmental disorder. Many causes have been proposed, but its theory of causation is still questionable and ultimately unknown. Autism is believed to be largely inherited, although the genetics of autism are complex and it is unclear which genes are responsible. 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 any convincing scientific evidence.Andrew Wakefield published a small study in 1998 in the United Kingdom suggesting a causal link between autism and the trivalent MMR vaccine. After data included in the report was shown to be deliberately falsified, the paper was retracted, and Wakefield's medical license revoked.

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