What Really Causes Autism?


There are many possible causes of autism. (Photo: Getty)

With all of the fear and confusion surrounding what may (and may not) cause autism, many parents are hoping for one clear-cut culprit to emerge. But while a wealth of studies are finally shedding some light on what puts a child at risk for autism, researchers are discovering that there are many factors at play. In other words, it’s complicated. “The data we have thus far would suggest there are going to be multiple causes of autism,” David G. Amaral, PhD, research director of The MIND Institute at UC Davis, tells Yahoo Parenting.

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Some people have a genetic predisposition to autism spectrum disorders (ASD), but that’s only part of the picture. In general, the cause is more than likely a complex combination of genetics and environment. “There is some consensus that adversities during pregnancy increase the risk of a child developing autism,” Joachim Hallmayer, MD, associate professor of psychiatry and behavioral sciences at Stanford School of Medicine, tells Yahoo Parenting.

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Here’s a look at some of the latest research on the possible causes of autism (and one whose link to ASD has been debunked).

Gestational diabetes

A new study involving 320,000 children published in the Journal of the American Medical Association found that mothers diagnosed with gestational diabetes mellitus by 26 weeks were more likely to have infants with an increased risk of ASD. The timing of the diagnosis appears to be significant since women who had type 2 diabetes before becoming pregnant were not significantly associated with a risk of having a child with ASD.

The researchers note there may be several reasons why gestational diabetes appears to play a role in ASD, including the fetus experiencing lower levels of oxygen in the blood; oxidative stress in cord blood and placental tissue; and chronic inflammation.

Autoimmune diseases

A 2013 study of more than 2,400 mothers found that those with "anti-brain” antibodies are more likely to have children with autism spectrum disorders. Antibodies are your body’s way of fighting off disease-causing bacteria and viruses, but sometimes, antibodies attack their own tissues. In this case, they may harm an infant’s brain development and possibly lead to autism. The study found that mothers of an ASD child were four times more likely to have anti-brain antibodies than other women of childbearing age.

“It’s not clear why they’re generating these antibodies,” says Amaral, “but they’re directed at the fetal brain. These antibodies are not found in women with typically developing children or even in other children who go on to develop other neuro disorders.”

ASD mothers with anti-brain antibodies were also more likely to have an autoimmune disease, particularly rheumatoid arthritis and lupus, according to the study. More research is needed, but the study could lead to a biomarker for autism and possibly a drug that blocks these antibodies to prevent the condition.

Air Pollution

Exposure to air pollution during pregnancy (such as living near high-traffic areas and freeways) is associated with having an autistic child, according to a study published in Environmental Health Perspectives. And timing matters: Researchers found a link between a greater chance of having a child with ASD and air pollution exposure during pregnancy, particularly the third trimester, but not before or after pregnancy. In general, the greater the exposure to air pollution, the higher the risk of having a child with ASD. According to the study, polluted air contains toxins linked to neurotoxicity during pregnancy.


Although the fear of vaccines lives on (case in point: The US experienced a record number of measles cases in 2014, according to the Centers for Disease Control and Prevention), the small, flawed, and falsified study that propagated the idea that the measles, mumps and rubella (MMR) vaccine causes autism has been debunked and retracted. Meanwhile, multiple studies have confirmed there is no autism-vaccine link. Most recently, a study in the Journal of the American Medical Association involving more than 95,000 children looked at kids with and without siblings who had autism spectrum disorder and their rates of MMR vaccinations. The study found that, even in children who have a sibling with autism spectrum disorder that puts them at a higher risk of developing the disorder themselves, receiving the MMR vaccine was not associated with an increased risk of ASD at any age. “If it were the vaccines [causing autism], it would be terrific because it would be so easy to do something about it,” says Amaral. “But research shows there is no link [between autism and] vaccines.”

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