Controversies in autism

Diagnoses of autism have become more frequent since the 1980s, which has led to various controversies about both the cause of autism and the nature of the diagnoses themselves. Whether autism has mainly a genetic or developmental cause, and the degree of coincidence between autism and intellectual disability, are all matters of current scientific controversy as well as inquiry.

Scientific consensus holds that vaccines do not cause autism, but popular rumors and an article in a respected scientific journal, The Lancet, provoked concern among parents. The Lancet article was retracted for making false claims and because its author was found to be on the payroll of litigants against vaccine manufacturers.

Most recent reviews of epidemiology 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 on the autism spectrum 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 parental age and diabetes in the mother during pregnancy. ASD is associated with several genetic disorders and epilepsy. Autism is also associated with intellectual disability.

There is evidence that autism has a genetic component, and ongoing research focuses on finding the biomarkers that determine autistic phenotypes.

Genetics is viewed as an underlying factor because there is a statistical pattern for a significantly high risk to have another autistic child in families with an already affected child. However, while some parents of autistic children are progressively also being diagnosed on the autism spectrum, at least some autistic children have apparently neurotypical parents. This suggests to some that genetics are either not a necessary cause or that they don't play a part in all cases of ASD, although it could also mean that the gene(s) responsible may be recessive or a spontaneous mutation. The spectrum of autistic disorders is notable for its significant gender disparity, with the incidence of autism in males greatly exceeding the incidence in females. Whilst this could be evidence for a genetic theory, it has also been argued that male brains may be more vulnerable during early development.

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