Cause and Risk Factors for Autism

The cause of autism is unknown. The disorder results from abnormalities in brain structure or function and the underlying cause usually cannot be identified.

Patients with autism often have abnormalities in several areas of the brain. This may indicate that a disruption in fetal brain development contributes to the disorder. It may be that brain abnormalities result from genetic (hereditary) or environmental (e.g., exposure to toxins) factors, metabolic disorders (e.g., serotonin deficiency), viral infections (e.g., German measles) or complications during pregnancy and delivery.

A single gene for autism has not been identified, but a group of unstable genes may trigger the disorder in some patients. According to a recent study, approximately 11% of autism cases may have a genetic component. More research is necessary to evaluate a possible link between autism and immunizations like the measles-mumps-rubella (MMR) vaccine.

In November 2012, the results of a large study conducted in Denmark indicated a link between fever/flu during pregnancy and an increased risk for autism. According to the study, which was conducted from 1997 and 2003 and published in Pediatrics, autism was diagnosed twice as often in children whose mother had the flu during her pregnancy and three times as often in those whose mother had fever lasting a week or longer (from any cause) while she was pregnant. More research is needed to determine the exact cause of autism and autism spectrum disorders.

Medical conditions associated with an increased risk for autism include the following:

  • Fragile X syndrome (more common in males; may cause mental retardation)
  • Tuberous sclerosis (syndrome that causes seizures, mental disorders, and tumors)
  • Congenital rubella syndrome (results from transmission of the rubella virus [causes German measles] in utero)
  • Untreated phenylketonuria (PKU; hereditary disease caused by a defective enzyme)

Publication Review By: Stanley J. Swierzewski, III, M.D.

Published: 29 Feb 2000

Last Modified: 01 Sep 2015