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What causes autism spectrum disorder (ASD)?

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Scientists don't know exactly what causes autism. Autism was first described in the 1940s, but very little was known about it until the last few decades. Even today, there is a great deal that we don't know about autism.

Because the disorder is so complex and no two people with autism are exactly alike, there are probably many causes for autism.

Genes & ASD

Genes: Bits of DNA that carry information about making the proteins that form your body.

Chromosomes: Packages of DNA in each cell in your body.

A great deal of evidence supports the idea that genes are one of the main causes of ASD. More than 100 genes on different chromosomes (pronounced KROH-muh-sohmz) may be involved in causing ASD, to different degrees.

People with autism have slight changes, called mutations (pronounced myoo-TEY-shuhnz), in many of these genes. However, the link between genetic mutations and autism is complex:

  • Most people with autism have different mutations and combinations of mutations. Not everyone with autism has changes in every gene that scientists have linked to ASD.
  • Many people without autism or autism symptoms also have some of these genetic mutations that scientists have linked to autism.

This evidence means that different genetic mutations probably play different roles in ASD. For example, certain mutations or combinations of mutations might:

  • Cause specific symptoms of ASD
  • Control how mild or severe those symptoms are
  • Increase susceptibility to autism. This means someone with one of these gene mutations is at greater risk for autism than someone without the mutation.

Interactions Between Genes and the Environment

If someone is susceptible to ASD because of genetic mutations, then certain situations might cause autism in that person.

For instance, an infection or contact with chemicals in the environment could cause autism in someone who is susceptible because of genetic mutations.1 However, someone who is genetically susceptible might not get an ASD even if he or she has the same experiences.2

Other Biological Causes

Researchers are also looking into biological factors other than genes that might be involved in ASD. Some of these include:

  • Problems with brain connections
  • Problems with growth or overgrowth in certain areas of the brain
  • Problems with metabolism (the body's energy production system)
  • Problems in the body's immune system, which protects against infections

  1. Landrigan, P. J. (2010). What causes autism? Exploring the environmental contribution. Current Opinion in Pediatrics, 22(2):219-25. [top]
  2. Hallmayer, J., Cleveland, S., Torres, A., Phillips, J., Cohen, B., Torigoe, T., et al. (2011). Genetic heritability and shared environmental factors among twin pairs with autism. Archives of General Psychiatry, 68(11), 1095-1102. doi: 10.1001/archgenpsychiatry.2011.76. [top]

Last Updated Date: 11/30/2012
Last Reviewed Date: 12/18/2013
Vision National Institutes of Health Home BOND National Institues of Health Home Home Storz Lab: Section on Environmental Gene Regulation Home Machner Lab: Unit on Microbial Pathogenesis Home Division of Intramural Population Health Research Home Bonifacino Lab: Section on Intracellular Protein Trafficking Home Lilly Lab: Section on Gamete Development Home Lippincott-Schwartz Lab: Section on Organelle Biology