1. Ada
  2. Conditions
  3. Autism
  4. Causes

Autism Causes

  1. Genetics
  2. Medications during pregnancy
  3. Congenital Rubella Syndrome
  4. Parental age and birth spacing
  5. Vaccines

Autism, or autism spectrum disorder (ASD), is a developmental disorder that affects the way a person communicates and interacts with other people, as well as the ways in which they behave and learn.[1]

The type and severity of autism symptoms vary from person to person. Autism is what is known as a spectrum disorder, meaning that people who live with the disorder can experience a wide range of symptoms at varying degrees of severity.[2] Some are more profoundly affected than others.

Scientists believe that both genetics and environment are involved in the development of autism. Most cases of autism spectrum disorders are idiopathic, which means that the cause is not known for certain. A minority of people with autism have secondary autism spectrum disorder, in which a specific cause has been found.[1]

Good to know: While research on the causes of autism is ongoing, the only factor that has been conclusively proven to be related to autism is genetics. Certain medications, rubella and other conditions are thought to be possible causative factors by some medical researchers, but, although there is often compelling evidence, links have not been fully proven. It is important to note that a large body of scientific research shows that there is absolutely no link between autism and vaccines.

Genetic causes of autism

In up to 25 percent of people with autism spectrum disorder, the condition is thought to have a genetic cause. Over 100 genes, many of which are involved with brain development, may be involved in causing autism.[2][3][4]

Good to know: Not everyone with the identified genetic mutations has autism. All human beings carry genetic mutations.

Autism can run in families, although it is not known exactly why this is. In cases of primary autism spectrum disorders, the brother of a child with autism is thought to have a 7 percent chance of developing autism, with an additional 7 percent chance of developing less severe autism spectrum symptoms. The sister of a child with autism is thought to have a 1 to 2 percent chance of developing autism, plus the additional chance of less severe autism spectrum symptoms.[1][2]

Medications taken during pregnancy

Valproic acid

Valproic acid, also called valproate, is used to treat seizures, mania in people with bipolar disorder and to prevent migraine headaches. Some large studies have shown that taking valproic acid during pregnancy increases the risk that the child will be born with serious birth defects and may increase the risk that the child will develop an autism spectrum disorder.[5][6][7][8]

The dosage and the time at which the drug was taken may affect the likelihood of increased risk of autism.[9] However, the link between autism and maternal use of valproic acid is not yet conclusively proven. Because of its toxicity, women who are pregnant or planning to become pregnant should not use valproate. The drug may also cause liver and pancreas damage to users.


Thalidomide is used to treat graft versus host disease (GVHD) in people who have received a skin graft or a donated organ. It is also used in the treatment of multiple myeloma. It is well known that thalidomide carries a risk of severe birth defects when taken by a person who is pregnant, and for this reason it is rarely used to treat adults if other treatments are at all available. Thalidomide can also be transmitted to a fetus through the father’s semen.

Several studies have shown that contact with thalidomide before birth, specifically in the first trimester of pregnancy, may increase the risk that a child will develop autism spectrum disorder.[9][10][11][12]. Research into this is ongoing.


Misoprostol is used to prevent ulcers. It can also be used to induce labor and, in high enough doses, terminate pregnancy in its early stages, although there is some evidence that it is not very effective for this, and many pregnancies continue to term. Several studies have indicated that there is some evidence to suggest that misoprostol use in the first trimester of pregnancy may cause autism spectrum disorder.[13]

However, the exact mechanisms and ways in which the drug may lead to increased risk of autism have not yet been fully explored, and there is still some debate about the role of misoprostol.

Congenital Rubella Syndrome

When a pregnant person is exposed to the rubella virus during the first trimester, the fetus has a high chance of developing congenital rubella syndrome (CRS). This condition can cause deafness, microcephaly, congenital heart disease and learning difficulties. Since the 1970s, it has been strongly suggested that congenital rubella syndrome seems to be associated with higher than usual incidences of autism spectrum disorder, though the link has not yet been conclusively proven.[14][15]

Good to know: Congenital rubella syndrome is very rare in the United States because of the country’s policy of universal immunization against rubella. A study estimated that over 1,000 cases of autism spectrum disorder were prevented by rubella vaccination in the U.S. between 2001 and 2010.[16] Not all cases of CGR lead to autism.

Learn more about Rubella »

Older parents and birth spacing

Age of the parents

Children born to older parents are more likely to develop autism. The risk increases in proportion to the parents’ age and seems to heighten significantly for each additional 10 years in maternal and paternal age.[17][18] There is some evidence emerging that developmental disorders such as autism have their origins very early during the prenatal phase.[19]

Time between births

A study by the Centers for Disease Control and Prevention suggested a connection between autism spectrum disorder and the amount of time between births for each mother. The study found that children who were conceived less than 18 months or more than 59 months (4 years and 11 months) after the previous birth were more likely to develop autism.[20] Several other studies have found that there is compelling evidence that very short or very long birth spacings both increase the risk of autism.[21] However, this link has not yet been fully established.

Autism and vaccines

There has been extensive research on vaccines and autism, and all scientific evidence indicates there is no link between autism and vaccines.[22][23][24][25]

Since 1998, studies supposedly linking the measles, mumps and rubella vaccine (MMR vaccine) to autism have led to a movement among some parents and medical practitioners to choose not to vaccinate children against both these and other infectious diseases. These studies have been discredited as scientifically unsound, but as a result of their impact, epidemics of formerly rare childhood diseases, such as measles, mumps, rubella and whooping cough have become more common.[26][27]

There is no evidence at all that the MMR or any other vaccines are a causative factor for autism. Concern over the possibility that vaccination might lead to autism is unfounded and should not prevent caregivers from ensuring that children for whom they are responsible are vaccinated.

Read more about autism, including diagnosis and management »

  1. National Human Genome Research Institute. “Learning About Autism.” January 2017. Accessed June 12, 2018.

  2. Genetics Home Reference. “Autism spectrum disorder.” June 2017. Accessed June 12, 2018.

  3. US National Library of Medicine. “The genetic landscapes of autism spectrum disorders.” July 2013. Accessed June 12, 2018.

  4. National Institute of Child Health and Human Development. “What causes autism?” January 2017. Accessed June 12, 2018.

  5. US National Library of Medicine. “Prenatal valproate exposure and risk of autism spectrum disorders and childhood autism.” April 2013. Accessed June 12, 2018.

  6. MedlinePlus. “Valproic Acid.” July 2017. Accessed June 12, 2018.

  7. Epilepsy Currents. “In Utero Valproate Exposure and Autism: Long Suspected, Finally Proven”. November 2013. Accessed 15 November 2018.

  8. Pathology Research International. “What We Have Learned about Autism Spectrum Disorder from Valproic Acid”. 2013. Accessed 15 November 2018.

  9. Emerging Health Threats. “Environmental risk factors for autism”. 2011. Accessed 15 November 2018.

  10. Centers for Disease Control and Prevention. “Basics About ASD.” May 2018. Accessed June 12, 2018.

  11. US National Library of Medicine. “Autism in thalidomide embryopathy: a population study.” April 1994. Accessed June 12, 2018.

  12. International Journal of Developmental Neuroscience. “Autism associated with conditions characterized by developmental errors in early embryogenesis: a mini review”. 2005. Accessed 15 November 2018.

  13. US National Library of Medicine. “Autism and Möbius sequence: an exploratory study of children in northeastern Brazil.” June 2003. Accessed June 12, 2018.

  14. Autism Society. “Causes.” July 2015. Accessed June 12, 2018.

  15. US National Library of Medicine. “Does Rubella Cause Autism: A 2015 Reappraisal?” February 2016. Accessed June 12, 2018.

  16. BMC Public Health. “Congenital rubella syndrome and autism spectrum disorder prevented by rubella vaccination - United States, 2001-2010.” May 2011. Accessed June 12, 2018.

  17. US National Library of Medicine. “Maternal and paternal age and risk of autism spectrum disorders.” April 2007. Accessed June 12, 2018.

  18. US National Library of Medicine. “Advanced parental age and the risk of autism spectrum disorder.” December 2008. Accessed June 12, 2018.

  19. Pediatrics. “Birth Spacing and Risk of Autism and Other Neurodevelopmental Disabilities: A Systematic Review”. 5 May 2016. Accessed 15 November 2018.

  20. Centers for Disease Control and Prevention. “Key Findings: Autism is Associated with Amount of Time Between Births.” December 2017. Accessed June 12, 2018.

  21. Pediatrics. “Interpregnancy Interval and Risk of Autism Spectrum Disorders”. October 2015. Accessed 15 November 2018.

  22. Autism Speaks. “What causes autism?” Accessed June 12, 2018.

  23. American Academy of Pediatrics. “Vaccine Safety: Examine the Evidence.” January 2017. Accessed June 12, 2018.

  24. Centers for Disease Control and Prevention. “Vaccines Do Not Cause Autism.” October 2015. Accessed June 12, 2018.

  25. Centers for Disease Control and Prevention. “Measles, Mumps, and Rubella (MMR) Vaccine Safety Studies.” August 2015. Accessed June 12, 2018.

  26. Journal of the American Medical Association. “Association Between Vaccine Refusal and Vaccine-Preventable Diseases in the United States: A Review of Measles and Pertussis.”. 16 September 2016. Accessed 13 November 2018.

  27. Cureus. “The Anti-vaccination Movement: A Regression in Modern Medicine.”. 3 July 2018. Accessed 13 November 2018.