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What Causes Autism?


Updated December 23, 2010

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

What Causes Autism?:

Most 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 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" that may be misdiagnosed as autism), most cases of autism are considered "idiopathic," meaning "without known cause." Some of the specific known causes of autism are listed at the end of this article.

A Controversial Topic:

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 can't take the place of solid research. This article provides an overview of some currently known causes as well as different theories that are either debunked or now under investigation.

For More on Autism Controversies:

Do Vaccines Cause Autism?:

Two theories link autism and vaccines. The first theory suggests that the MMR (Mumps-Measles-Rubella) vaccine may cause intestinal problems leading to the development of autism. The second theory suggests that a mercury-based preservative called thimerosal, used in some vaccines, could be connected to 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.

For More on Vaccines and Autism:

Is Autism Genetic?:

It is certain that some cases of autism have a genetic basis, and it is quite possible that genetics are involved with all cases of autism. Studies have shown many cases of "spontaneous" genetic mutation which are not inherited. In addition, studies have shown that parents from families with autistic members are more likely to have autistic children, and families with one autistic child are at increased risk of having more than one autistic child.

For More on Genetics and Autism:

Is Autism Caused by Bad Parenting?:

No. Dr. 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, whose book "The Empty Fortress: Infantile Autism and the Birth of the Self" created a generation of parents carrying the guilt for their child's disability. Fortunately, our generation is spared that burden.

For More on Refrigerator Mothers and Autism: Is Autism Caused by Bad Parenting?

Is Autism Caused by Differences in the Brain?:

Some researchers have found differences between the autistic brain and the typical brain. Autistic individuals seem to have larger brains. They also seem to process information differently; in other words, their brains are "wired" differently. Research on this issue is ongoing, and intriguing findings are coming out of top research institutions.

For More on Autism and the Brain:

Is Autism an Immune Deficiency Problem?:

There is some evidence that autism is linked to problems in the immune system. Autistic individuals often have other physical issues related to immune deficiency. Some researchers say they have developed effective treatments based on boosting the immune system. The NIH, however, states that the evidence is not yet strong enough to show a causal relationship.

Is Autism Caused By Food Allergies?:

There is some evidence that allergies to certain foods could contribute to autistic symptoms. Most people who hold to this theory feel that gluten (a wheat product) and casein (dairy) are the most signficant culprits.

For More on Autism and Food Allergies:

Is Autism Caused By Poor Nutrition?:

It seems unlikely that malnutrition can cause autism. But megavitamin therapies have been used for many years to treat autistic symptoms. Certain supplements, particularly omega fish oils, do seem to be helpful for treating some aspects of autism.

For More on Autism and Nutrition: Is Autism Caused By Poor Nutrition?

So...What DOES Cause Autism?:

Just some of the issues known to cause autism include: In addition to these rare, documented causes, some studies point to higher risk of autism associated with older parenthood, certain types of pollution and a variety of other issues:

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. Could your individual child have developed autism as a result of heredity? Could he or she have been exposed in utero to something that caused a neurological anomaly? Could some post-natal exposure be to blame? As of the writing of this article, all of those possibilities are still under investigation.


Caglayan, A. (2010). Genetic causes of syndromic and non-syndromic autism. Developmental Medicine & Child Neurology, 52(2), 130-138. doi:10.1111/j.1469-8749.2009.03523.

CDC Page on Vaccine Safety

Exploring Autism

"Finding Supports Theory That Autism Results From Failure of Brain Areas To Work Together" NIH News, November 2004.

The Autism Institute.

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