Modern Medicine

Scientists narrow down the startling risk factors that can cause autism

Alexandra Ossola, special to
Key Points
  • About 1 in 68 children are diagnosed with autism.
  • Researchers estimate that there may be hundreds of genes that could influence the development of autism.
  • Mothers who have bacterial or viral infections during pregnancy or those who are obese are more likely to give birth to babies who later develop autism.
  • Childhood or prenatal exposure to toxic chemicals, such as pesticides and hormone-disrupting phthalates (often found in plastics) and some found in air pollution, play a role.
Scientists hone in on the risk factors that can cause autism

Amidst the media hubbub of the new presidential administration, autism was back in the news. Well-known vaccine skeptic Andrew Wakefield attended one of President Donald Trump's inaugural balls; Robert F. Kennedy Jr., an environmental attorney and outspoken critic of vaccines, claimed that Trump had asked him to chair a commission on "vaccine safety and scientific integrity," though seven months after those initial reports no concrete plans for such a commission have been made public. Both Wakefield and Kennedy have expressed their doubts about the safety of vaccines on the basis that they may be linked to increased incidence of autism.

For many researchers working to find the causes of autism, this is frustrating, if well-tread, rhetoric. "Regarding vaccines, the case has been closed for many years as far as the evidence is concerned," says Mayada Elsabbagh, an assistant professor of psychiatry at McGill University. Alycia Halladay, the chief science officer at the Autism Science Foundation, called the discussion about vaccines and autism a "distraction" because money spent looking into it isn't being dedicated to more pressing research questions.

In the past decade, researchers have come a long way in narrowing down which conditions may make autism more likely to develop. What they learn could lead to more sophisticated treatments for autism at its early stages, or even prevent the disorder from developing in the first place.

Ritesh Uttamchandani | Hindustan Times | Getty Images

Autism Spectrum Disorder, or autism for short, is a disorder that can affect how the brain develops. It's characterized by social challenges, difficulties in communication and behavioral issues, according to the Centers for Disease Control and Prevention. Symptoms usually appear in children between 12 and 18 months old. And the effects of autism can range from slight social challenges to severe cognitive impairment.

"If you've met one person with autism, you've met one person with autism — everyone looks a little different," says Heather Volk, an assistant professor in the department of Mental Health at the Johns Hopkins Bloomberg School of Public Health.

About 1 in 68 children are diagnosed with autism, according to the CDC. Today the Autism Society estimates that 3.5 million Americans are living with an autism spectrum disorder, and the prevalence has been rising over time, increasing by 119.4 percent between 2000 and 2010, according to the CDC. Though that's likely also driven by greater awareness of the condition and its symptoms, as well as access to services, Elsabbagh says. A 2014 study found that it costs $2.4 million to support a person with autism and an intellectual disability (which appears to affect 40 percent to 60 percent of those with autism) throughout the course of his or her life.

Cracking the genetic code

Scientists spent decades looking for a specific gene, or a specific part of the brain, that could be causing the symptoms of autism. But that work hasn't turned up any one specific answer. Instead, researchers have had to change their questions. They now suspect that autism, like other complex diseases such as cancer or obesity, comes about by the interaction of many different genes and environmental factors. Researchers estimate that there may be hundreds of genes that could make someone more likely to develop autism, but merely having any one of those genes doesn't determine whether or not the disorder develops, or how severe it is if it does.

Through careful epidemiological studies conducted on large populations, a number of scientists, including Craig Newschaffer at Drexel University and Peter Bearman at Columbia University, have been able to point to some factors that correlate to the risk of autism. Over the years, researchers have determined that childhood or prenatal exposure to toxic chemicals, such as pesticides ; hormone-disrupting phthalates (often found in plastics) and some found in air pollution, have played a role. Mothers who have bacterial or viral infections during pregnancy or those who are obese are also more likely to give birth to babies who are later diagnosed with autism.

It's important to note, however, that these are risk factors for autism, not causes — there's a correlation between these factors and autism, but researchers aren't quite sure of the mechanism that might make the disorder more likely to develop.

Red flags

Researchers are getting creative with the kinds of studies they are designing to better assess these and other potential risk factors. One long-running study at the University of California, Davis tracks a huge array of children's genetic and environmental factors in children as young as two years old to compare those that develop autism to those that do not. Other research efforts start even earlier, tracking moms — since autism seems to run in families, scientists are recruiting mothers who already have one child with autism, then recruit the next sibling.

"If you do this during pregnancy, you can give the mom questionnaires in real time and ask her things like where she drove, what she ate," Volk says. Plus, you can take samples from the mother during her pregnancy or even image the fetus' brain as it develops.

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But even if a well-designed study uncovers a new risk factor, that has to be validated and replicated by other scientists. And so far, Volk says, researchers are not far enough down the road to come up with any interventions to treat or prevent autism based on those findings. There are some findings that, if reflected in policy, are generally beneficial, such as having cleaner air and making baby bottles that are BPA-free. "But we're not far enough to think about pharmacological interventions in pregnancy," Volk says.

I don't think [understanding autism] is an unsolvable problem. I don't think any autism researcher would be doing it if it were.
Alycia Halladay
chief science officer at the Autism Science Foundation

Right now the most effective interventions for autism take place after a child has begun to show symptoms. "The best way for us to support children with autism is to support parents so that they interact with children and address concerns with children together," Elsabbagh says.

Programs are popping up all over the world to help parents do exactly that—to modify their own behavior towards children with autism so that, over time, the children's brains develop in the most optimal way possible. In the US, some of those programs include the UC Davis MIND Institute, the Center for Autism and the Developing Brain in New York and the Semel Institute for Neuroscience and Human Behavior at UCLA. Researchers are working on how to make these costly programs available to all families who need them, Elsabbagh says.

It's not clear what future interventions might look like. But scientists are working on it. "I think the best thing we can do as scientists is ask smart questions and follow the data where it seems to point," Volk says.

Sometimes, that process is time consuming or surprisingly complex. "I think maybe the challenge in that type of reporting is that science changes incrementally. We make small discoveries over time," Elsabbagh says.

And though they've been at it for decades, researchers are hopeful that they can unravel autism to provide more effective interventions for people with autism. "I don't think [understanding autism] is an unsolvable problem. I don't think any autism researcher would be doing it if it were," says Halladay of the Autism Science Foundation.

According to the National Autism Association, a person with autism may:

Not respond to his or her name.
Have obsessive interests.
Avoid eye contact or physical contact.
Have difficulty understanding, or showing understanding, of others' feelings or their own.
Repeat words or phrases.
React more or less sensitively than usual to sounds, smells, tastes, sights or physical sensations.

— By Alexandra Ossola, special to