Causes and Risk Factors of Autism

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Many parents wonder whether something they did—or didn't do—might have caused their child's autism. While it is possible to nail down the cause of autism spectrum disorder (ASD) in some children, most parents will never find a definitive answer to their question. Though quite a few rare genetic disorders and toxic exposures are known to cause autism (or autism-like symptoms), most cases are considered idiopathic, meaning "without known cause."

Common Causes

In most cases, a child's autism cannot be associated with a specific cause. As research progresses, it may be that both genetics and the environment are involved. Some researchers have found differences between the autistic brain and the typical brain. People with autism seem to have larger brains and they also seem to process information differently. In other words, their brains are "wired" differently. Research on this issue is ongoing, with intriguing findings coming out of top institutions.

There are a few relatively rare known causes of autism, including:

  • Depakote (also called Valproatean)—an anti-seizure medication taken during pregnancy
  • Fragile X syndrome—a genetic disorder
  • Rubella
  • PKU
  • Tuberous sclerosis—a rare genetic disorder
  • Prader-Willi syndrome—a rare genetic disorder

Vaccines do not cause autism. If you had your child vaccinated, you did not cause his or her autism. The medical community has soundly refuted these theories, but a very passionate group of parents and researchers continue to disagree based on anecdotal evidence.

Risk Factors

In addition to these rare, documented causes, some studies point to a higher risk of autism being associated with older parenthood, certain types of pollution, and a variety of other issues. Association, however, is not the same thing as causation. It may be, for example, that older parents are associated with autism because they are more likely to have autism themselves and thus have a harder time finding a mate.

These risk factors have been seen:

  • Sex: Autism spectrum disorder is four times more likely in boys than in girls.
  • Family history of autism
  • Preterm birth (before 26 weeks gestation)
  • Older parental age

In certain cases, autism is associated with problems in the immune system. People with autism often have other physical issues related to immune deficiency. The National Institutes of Health (NIH), however, states that the evidence is not yet strong enough to show a causal relationship.

There is also some evidence that children with autism are more prone to gastrointestinal (GI) problems, allergies, and food intolerances than other children, but no evidence that these cause autism.


Researchers are certain that some cases of autism have a genetic basis. So, it is quite possible that genetics are involved in all cases of autism.

Many studies have shown that parents from families with autistic members are more likely to have autistic children. In addition, families with one autistic child are at increased risk of having more than one autistic child.

Interestingly, however, "genetic" and "hereditary" are not the same thing. Studies have shown many cases of spontaneous genetic mutation associated with autism. Spontaneous genetic mutation, as the name implies, just happens—usually for unknown reasons. In other words, a child can be born with genetic differences which are not inherited, but which may be associated with autism.

Lifestyle Risk Factors

Children with autism are often very sensitive to tastes and textures, and thus have limited diets. It may be the case that they are lacking specific nutrients important to learning and social/intellectual growth. While improved nutrition may be a helpful therapy, it seems unlikely that malnutrition can cause autism.

Researchers have done a great deal of work to determine that certain things do not cause autism. Why work so hard to disprove theories? Because several theories related to autism have led to untold emotional pain, risky behavior, and even some deaths. Avoiding vaccines not only won't prevent autism, but it also places your child (and other children) at risk of diseases that can kill them.

For example, Dr. Leo Kanner, the man who first identified autism as a unique condition, had the idea that cold “refrigerator” mothers caused autism. He was wrong. But Dr. Kanner's misinterpretation of autism impressed a major figure in psychology, Bruno Bettelheim. Bettelheim's book, "The Empty Fortress: Infantile Autism and the Birth of the Self," created a generation of parents who carried guilt for their child's disability. Fortunately, that burden is no longer.

As you explore the question of "what causes autism," you are likely to come across many individuals who are absolutely certain they know the answer. It's important to know, though, that the subject is highly controversial and one parent's (or researcher's) passionate statements doesn't take the place of solid research.

A Word From Verywell

You'd think that with so much information available, someone could tell you what caused autism in your child. But the odds are you'll never know. All possibilities are still under investigation. And it can be very frustrating to live with a disorder—whether as a parent or child—when you know little about its cause.

The reality, however, is that the vast majority of parents did nothing to cause their child's autism and have no cause for guilt or self-recrimination. While parents may not discover the cause of their child's autism, they can do a great deal to ensure that their child reaches his/her potential and lives the fullest and happiest life possible.

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