What Causes Autism? Everyday Health MenuNewslettersSearch Autism What Causes Autism Here Are the Possible Genetic and Environmental Risk Factors Current research points to some clear genetic and environmental risk factors for autism from mutating genes during the development of a fetus to the age of parents when a child is born. By Brian MastroianniMedically Reviewed by Samuel Mackenzie, MD, PhDReviewed: April 3, 2018Medically ReviewedWhat exactly causes autism remains somewhat elusive, but research suggests both genetics and environmental factors play a role.Roy Scott/Getty Images Autism affects millions of people worldwide — one in every 68 children falls on the autism spectrum in the United States alone. Yet what exactly causes autism spectrum disorders (ASD) still remains somewhat elusive. (1) Research, however, has identified certain risk factors — both environmental and genetic — that have been associated with the developmental disorder. The conundrum is that while not everyone with these risk factors necessarily has autism, the disorder is more prevalent in people with such characteristics, explains Jeremy Veenstra-Vanderweele, MD, director of child and adolescent psychiatry at Columbia University College of Physicians and Surgeons. “Not everyone who will be exposed to some of the genetic or environmental risk factors for autism will be diagnosed,” he says. “There is no guarantee that a person will be on the spectrum. But it is important for people, especially parents and family members of children, [to know] what these potential factors are." Here are some of those risk factors. Autism May Be in Your Genes Dr. Veenstra-Vanderweele says that right now huge strides are being made in understanding the genetic risk factors for autism. More than 100 genes have been linked to autism. (2) This doesn’t mean that if someone has one of those specific genes they’ll have autism; it means autism is more prevalent in people with those 100 genes. Because there’s no one genetic combination that can predict autism, it’s likely that the genes associated with the disorder play a role in determining where someone falls on the spectrum, severity of symptoms, and susceptibility to developing problems in the first place. It might be, for example, that someone with a specific gene linked to autism will develop the disorder only if they are exposed to another risk factor, such as coming in contact with certain chemicals or pollutants. (See more on environmental risk factors below.) Conversely, someone without the gene who came in contact with those other risk factors might not develop autism either. In approximately 20 percent of children with autism, doctors can identify a specific gene or genetic abnormality associated with the disorder, Veenstra-Vanderweele says. (3) It also means that autism is more likely to run in families. (Though it’s worth noting that not all children of parents with a history of autism will necessarily have the disorder.) “You can find autism in children who come from parents who may be quite healthy, who might not exhibit any signs of ASD,” he says. “But on the genetic side, the parents could have precursor genes that could contribute to autism risk.” One recent study pointed to a new genetic risk factor for ASD — postzygotic mosaic mutations (genetic abnormalities that become abnormal after conception) — which were shown to contribute to autism risk in about 3 to 4 percent of the children in the study with the disorder. (4) The study included 2,300 families who had a single child with autism. Veenstra-Vanderweele says much more research is needed to better understand the seemingly complex role genetics plays in autism spectrum disorders. Certain Pregnancy Complications Drugs and Other Environmental Factors May Play a Role in Autism In addition to your genetic makeup, other factors in the environment, like your mother’s health during her pregnancy with you and certain chemicals she was exposed to, may play a role in determining who develops autism. (Note that scientists mean any nongenetic cause when they use the term “environmental risk factors” for autism.) (5) Conclusive and definitive research on what these risk factors are, however, is scant, according to a review paper published in the March 2017 issue of the journal Molecular Autism. (6) Remember in the example of the individual with the gene associated with autism, having that gene didn’t necessarily mean the individual would have autism? Similarly, for the environmental factors known to contribute to autism risk, none of the factors necessarily or definitively mean an individual will develop autism. Some of the environmental risk factors that have been linked to autism risk include: (7)Having a parent who was older when you were bornMalnutrition in your mother during pregnancy with youComplications during pregnancy or birthPregnancies spaced less than one year apart Other factors with inconclusive evidence as to their role in the development of autism include: exposure to air pollution, mercury, and heavy metals, according to the 2017 Molecular Autism paper. (6) And finally there is a growing body of research looking at potential connections between psychiatric disorders and autism, including some preliminary evidence that suggests autism risk may be increased in children whose mothers took certain antidepressant medications during pregnancy, according to a study published on July 19, 2017, in the BMJ. (8) That said, the potential relationship between prenatal antidepressant use and autism is still not well understood and more data is needed, Veenstra-Vanderweele adds. (In an editorial that accompanied the antidepressant-autism study in BMJ, another expert agreed.) (9) There Is NO Scientific Evidence That Vaccines Cause Autism A much-talked-about report from the 1990s claimed there may be a link between certain vaccinations given during infancy and autism. Those claims have since been debunked by subsequent studies — and the “evidence” behind those earlier claims has been found to be unreliable. (10) The American Academy of Pediatrics has compiled a list of dozens of studies that have found there is NO connection between childhood vaccines (or the ingredients in them) and autism. (11) The Centers for Disease Control and Prevention has said the same. (12) Veenstra-Vanderweele says that this train of thought is dangerous. Vaccinate your children. He says there is no scientific evidence that pinpoints vaccinations as a cause of autism. NEWSLETTERS Sign up for our Healthy Living Newsletter SubscribeBy subscribing you agree to the Terms of Use and Privacy Policy. Editorial Sources and Fact-Checking Autism Spectrum Disorder. Centers for Disease Control and Prevention. March 10, 2017.What Causes Autism? National Institute of Child Health and Human Development. January 31, 2017.Autism Spectrum Disorder. National Institute of Mental Health. October 2016.Exonic Mosaic Mutations Contribute Risk for Autism Spectrum Disorder. American Journal of Human Genomics. August 31, 2017.Environmental Factors in Autism Initiative. Autism Speaks. 2018.Environmental Risk Factors for Autism: An Evidence-Based Review of Systemic Reviews and Meta-Analyses. Molecular Autism. 2017.What Causes Autism? Autism Speaks.Rai, D, et al. Antidepressants During Pregnancy and Autism in Offspring: Population Based Cohort Study. BMJ. July 19, 2017.Schendel, DE. Prenatal Antidepressant Use and Risk of Autism. The British Medical Journal. July 19, 2017.Plotkin, S, et al. Vaccines and Autism: A Tale of Shifting Hypotheses. Clinical Infectious Diseases. February 15, 2009.Vaccine Safety: Examine the Evidence. American Academy of Pediatrics. January 26, 2017.Vaccines Do Not Cause Autism. Centers for Disease Control and Prevention. 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