What Causes Autism?

Flickr photo by KOMUnews
For some parents, one of the scariest things they can hear is that their child has autism. They wonder if they did anything to cause it. They wonder if they could have done something to prevent it. But autism is a mysterious disease, and no one knows for sure what triggers it.

We do know that it's increasing. Autism rates have soared nationwide in the past three decades -- from 1 in 10,000 children in the 1980’s, to 1 in 500, to 1 in 250, to 1 in 150. Today, autism affects 1 in 100 children (1 in every 58 boys).

We do know some of the children it affects. According to the National Institutes of Health, autism is more prevalent in certain groups of people: boys, siblings of those with autism, and people with certain other developmental disorders (Fragile X syndrome, for example).


Some research suggests that autism rates are much higher in some parts of the U.S. than others. For example, a child born in northwest Los Angeles is four times as likely to be diagnosed with autism as a child elsewhere in California. Scientists are still trying to figure out whether those differences reflect higher actual risk or a difference in awareness among residents.

Autism varies by state, too. According to Fighting Autism, Minnesota had the highest prevalence of 8-year-old children with autism in public schools in 2008-2009; Vermont had the lowest.

While no one knows for sure what causes most cases of autism, researchers are trying their best to find out. Here, some of the most popular theories.

Theory 1: Vaccines Cause Autism

  • According to the journal Pediatrics, one in four parents currently believes that some vaccines cause autism in healthy children.

  • A 1998 study by Andrew Wakefield published in The Lancet showed the possibility of a link between the mumps-measles-rubella (MMR) vaccine and autism. A 2009 investigation into his research found that Wakefield had fixed his data. Earlier this year, The Lancet issued a full retraction of the study.

Theory 2: Autism is a Genetic Disease


Theory 3: The Age of the Parents Adds to Autism Risk

  • A 10-year study published in the February 2010 issue of Autism Research suggests that the risk of having a child with full syndrome autism increases with maternal age. The researchers examined 4.9 million births in the 1990s.

  • A 2007 Kaiser Permanente study conducted in California reported that autism risk increased with both the mother's and father's age.


Theory 4: Environmental Toxins Pay a Role in Autism

  • In a January 2010 article "What Causes Autism? Exploring the Environmental Contribution," in the medical journal Current Opinion in Pediatrics, Philip J. Landrigan, M.D., a professor of Pediatrics at Mount Sinai School of Medicine in New York, calls for more research into the autism-environment link. He writes, "[The] likelihood is high that many of the materials ... have potential to cause injury to the developing brain and to produce neurodevelopmental disorders, possibly autism among them." His short list of "human developmental neurotoxicants": lead, methylmercury, polychlorinated biphenyls (PCBs), arsenic, manganese, organophosphate insecticides, DDT and ethyl alcohol.

  • A 2009 study in the journal Epidemiology says that environmental culprits may be to blame for autism: pesticides, viruses, and chemicals in household products.

  • Studies have found that disproportionate numbers of children develop autism after they're exposed to medications in the womb -- thalidomide, misoprostol, and valproic acid. Of children born to women who took valproic acid early in pregnancy, 11 percent were autistic.

  • A 2007 study done by the University of California at San Francisco showed a link between toxins in breast milk and developmental disorders.The study was done on rats, but researchers were alarmed that women are being exposed to certain widespread environmental chemicals (PCEs and PBDEs) that may add to the risk of onset of these developmental disorders in children.

Whatever the "real" cause(s), it's important that research continues, as it will lead the way to better therapies -- and maybe even prevention in some cases. There are currently several large studies underway which may shed some light on the causes of autism.

  • The National Children's Study -- "This study will examine the effects of environmental influences on the health and development of 100,000 children across the United States, following them from before birth until age 21. The study defines environment broadly, taking a number of natural and man-made environmental, biological, genetic and psychosocial factors into account. Findings from the study will be made available as the research progresses, making potential benefits known to the public as soon as possible."

  • The Study to Explore Early Development -- "SEED is a multi-year study funded by CDC. It is currently the largest study in the United States to help identify factors that may put children at risk for autism spectrum disorders (ASDs) and other developmental disabilities."

Let's all hope that these studies solve the autism mystery, and let's do our part by helping to spread the word about autism awareness.

What's your theory about what causes autism?


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