What Causes Autism In Children? 6 Facts You Need to Know

While there are many misconceptions about what causes autism in children, we've separated the facts from fiction. Here's everything you need to know.

child playing board game
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There is a lot that isn't fully known about autism, but researchers do believe there is a genetic component. So, for example, if you have autism, it's more likely your child will too. Although the severity of autism can vary widely, many children with the neurological disorder—which typically appears in the first three years of life—have problems speaking, interacting with others, sharing affection, and learning.

Nancy Wiseman had a feeling early on that something wasn't quite right with her daughter. When Sarah was 6 months old, she stopped babbling, and by 10 months, she was silent. By 18 months, the increasingly aloof toddler no longer responded to her name, and she resisted being held, kissed, or touched. "I felt that I was losing my child a little more each day," says Wiseman, of Merrimac, Massachusetts. When Sarah wasn't saying any words or even making sounds that resembled words by 20 months, her grandmother, a school psychologist, suspected that the girl might actually be deaf. Instead, Wiseman learned that her daughter had autism. "The diagnosis really knocked the wind out of me," she recalls, "but I was relieved to finally know what was wrong."

Thanks to the tireless efforts of parents and advocates, public awareness of autism has grown tremendously since it was first identified in 1943, but it is gaining even more attention today than ever before. Congress has held hearings on the condition. Public-health agencies are spending millions to study it. Researchers at countless universities are racing to find the causes and best treatments.

"There are many unanswered questions," says Alice Kau, Ph.D., an autism expert at the National Institutes of Health, which funded more than $74 million in autism research in 2002, as compared with only $22 million in 1997. Still, researchers are beginning to make progress in unraveling this baffling disorder.

Here are six facts about autism that every parent should know, from what does (and does not) cause autism to how early intervention may be key.

Autism May Be Genetic

While scientists do not know what causes autism, there may be a genetic component. According to the U.S. Department of Health and Human Services, autism tends to run in families. What's more, evidence now suggests that mutations of certain genes can increase one's risk of becoming autistic. Still, it's important to note that this link is complex. "Most people with autism have different mutations and combinations of mutations," an article by the National Institute of Health (NIH) explains. "Not everyone with autism has changes in every gene that scientists have linked to ASD."

Environmental Factors Can Play a Role

Many conditions can be caused by environmental factors, including autism. Some chemicals can (and do) increase your risk. However, the NIH explains this increased risk is usually combined with other factors.

"If someone is susceptible to [autism, or] ASD because of genetic mutations, then certain situations might cause autism in that person," NIH writes. "For instance, an infection or contact with chemicals in the environment could cause autism in someone who is susceptible because of genetic mutations.However, someone who is genetically susceptible might not get an ASD even if he or she has the same experiences."

Vaccines Have Not Been Linked to Autism

Even though there's been widespread controversy about a possible connection between vaccines and autism, according to the Centers for Disease Control and Prevention (CDC), vaccines do not cause autism. Some parents of children whose autistic symptoms first appeared shortly after their measles-mumps-rubella (MMR) immunization are convinced the shot was the cause, but repeated studies have failed to find scientific evidence.

What's more, the one small scale—and heavily criticized—study which suggested otherwise has been retracted and debunked. In January 2011, the British Medical Journal publicly denounced Dr. Andrew Wakefield, the author of the study. They cited the research as "fraudulent," stating he had "falsified data" and tampered with his research results to give the MMR vaccine bad publicity.

"Any apparent association [between vaccines and autism] is a coincidence," says Neal Halsey, M.D., director of the Institute for Vaccine Safety at Johns Hopkins University, in Baltimore. Up to 40 percent of children with autism typically experience regression at 12 to 18 months; they start developing normally but then suddenly lose communication and social skills. Parents may also notice symptoms at this age not because of the MMR vaccine but because of when it is administered, i.e. the MMR vaccine is routinely given at 12 to 15 months—when the first symptoms of autism often become noticeable.

The possibility that mercury poisoning might cause autism is also a concern. Since the 1930s, a preservative called thimerosal, which contains small amounts of mercury, had been used in some childhood vaccines (not MMR). Although mercury is known to be harmful to the brains of infants and young children, most vaccine experts say the amounts used in the preservative were too tiny to cause neurological damage. Nevertheless, manufacturers voluntarily began removing thimerosal in 1999, and by the end of 2001, none of the routine vaccines given in early childhood contained the preservative. The preservative is now used only in flu shots and some vaccines given to adults and adolescents.

Infections During Pregnancy Can Increase Your Child's Autism Risk

While vaccines haven't been linked to autism, exposure to infection in the womb seems to increase a child's risk. A study released in March 2019 and published in JAMA Psychiatry analyzed 1,791,520 Swedish children. It found that if a pregnant person suffered from a severe infection, their child was 79% more likely to be diagnosed with autism spectrum disorder. The increase was found with both major infections (like sepsis, pneumonia, meningitis, and flu) and minor infections (like urinary tract infections). Dr. Kristina Adams Waldorf, co-author of the study, said the results should encourage pregnant people to get the flu shot, which is safe for pregnancy and can prevent serious complications.

Other Biological Factors Can Contribute to Autism

In addition to genetic and environmental factors, certain biological components can increase one's risk of autism. These include, but are not limited to:

  • Problems with brain connections
  • Problems with growth (or overgrowth) in certain areas of the brain
  • Problems with metabolism
  • Problems in the body's immune system, which protects against infections

Early Autism Treatment Is Crucial

There is no known cure for autism, but intensive therapy can help children learn a wide range of skills, from making eye contact to hugging to having a conversation. Because children with autism have very different behaviors and abilities, the most effective approach takes into account a child's unique challenges and encourages healthy development through play, rather than just trying to change specific symptoms.

And the sooner a child begins, the better. A panel of experts convened by the National Academy of Sciences in 2001 recommended that children should have 25 hours of therapy per week as soon as autism is suspected.

"Intervention can take many forms, from going to a regular preschool to a parent's working with her child over the course of a normal day to direct therapies from well-trained teachers and professionals—all depending on the child," says Catherine Lord, Ph.D., director of the Center for Autism and Communication Disorders at the University of Michigan, in Ann Arbor.

Thanks to early intervention, some children—like Nancy Wiseman's daughter, Sarah—make remarkable progress. "At the very least, we're able to lessen the severity of symptoms," says Dr. Lord. "The latest studies show that almost 80 percent of kids with autism now have some speech by age 9, whereas only 50 percent of these kids were talking 20 years ago." And though past research suggests that most autistic children have below-average cognitive abilities, a recent study found that early treatment raised children's IQ scores by about 20 points, to almost normal levels. Those who started therapy as toddlers were also more likely to attend regular kindergarten.

Updated by
Kimberly Zapata
Kimberly Zapata

Kimberly Zapata is the Associate Editor at Parents. Her parenting, health, and wellness work has been published on numerous websites, including Health, Healthline, Parade, Washington Post, Huffington Post, Oprah, The Mighty, Mic, and Vice. She is also the founder and creator of Greater Than: Illness, an organization dedicated to empowering teens and young adults struggling with mental illness. And when she is not writing—or working—she is caring for her two children, aged 8 and 3.

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