What are the causes of autism?

The causes of autism are hard to pin down. A lot of people "know" what causes autism, but their explanations often don't stand up to scientific scrutiny. Here are a few of the theories you're likely to run into.

Vaccines and autism. In the late 1990s and early 21st century, people noticed that the percentage of children being diagnosed with autism was on the rise, pretty much at the same time that more and more children were being vaccinated for more and more diseases. It was reasonable to wonder whether something in the vaccines was causing neurological changes in a lot of children and contributing to, if not causing, symptoms of autism in many of them. And since many children begin receiving vaccines right around the time these symptoms become noticeable, many parents noticed soon, or immediately, after having their children vaccinated that their children's behavior "didn't seem quite right", and attributed the "changes" they observed to the vaccines.

Vaccines and autism. In the late 1990s and early 21st century, people noticed that the percentage of children being diagnosed with autism was on the rise, pretty much at the same time that more and more children were being vaccinated for more and more diseases. It was reasonable to wonder whether something in the vaccines was causing neurological changes in a lot of children and contributing to, if not causing, symptoms of autism in many of them. And since many children begin receiving vaccines right around the time these symptoms become noticeable, many parents noticed soon, or immediately, after having their children vaccinated that their children's behavior "didn't seem quite right", and attributed the "changes" they observed to the vaccines.

Quite a bit of research has been done to see if there is a link between immunizations and autism, and it's pretty clear by now that vaccines are not to blame. Children who go unvaccinated, and children who are vaccinated later in life, develop autism at the same rates as children who receive vaccines on the schedule recommended by the medical community. 

The Autism Science Foundation web site provides more information about the research on autism and vaccines.

Mercury and autism. Along with the "vaccines and autism" scare came the hypothesis that it was thimerosal, a mercury-based preservative used in many vaccines, that caused neurological changes resulting in autism. This, too, was understandable, since mercury is a known neurotoxin. However, the makers of vaccines stopped using thimerosal years ago and the rate of autism diagnoses has continued to increase. The site linked above also provides information about research on mercury and autism.

Genetic causes of autism. Autism runs in the family, so it makes sense to wonder about, and do research on, possible genetic causes of autism. Studies of identical twins have shown that if one has autism the other has about an 80 to 90 percent chance of also having it; however, if a fraternal twin has autism, the likelihood of the other also having it is only 3-10%, the same as for siblings who are not twins. This is still higher than the one in 88 chance we find in the general population. 

This does not necessarily mean there is a gene that directly causes autism. In fact, researchers have identified about 20 different genes that increase or decrease a person's chances of being on the autism spectrum. 

Environmental factors. It could be that some people's genetic makeup makes them vulnerable to environmental factors that cause autism in some people and not in others. Increased risk of autism has been associated with food allergies, parental age, and exposure to certain pesticides and pharmaceuticals. If these factors result in symptoms of autism in some individuals but not others, it could be that a combination of environmental toxins and a genetic predisposition to autism is necessary for symptoms to appear.

We may never know exactly what causes autism. However, as we learn more about autism, we learn more about how to help people on the spectrum live more independent, more fulfilled, more productive lives.

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