In the 1940s, experts described the first cases of autism. Then, the debate started. What caused the disorder? What can families do to protect their children?
Even in 2020, we don't have answers to many of these questions.
The National Institutes of Health explains that science shows many factors contribute to autism. They intertwine and interconnect in vulnerable people, and when they do, the disorder emerges.
Autism can also look very different in different people, and that makes accurate diagnoses and comparisons hard for researchers.
Some factors, including premature birth and late-life pregnancies, are accepted autism causes. But others, including environmental triggers, are hot spots of ongoing research.
Here's what we know right now about the disorder and how families can prepare.
The Role of Genetics
Genes pass from parents to children at conception. While researchers don't know what specific genes trigger autism spectrum disorder (ASD), they know that genetic data plays a large role in susceptibility.
In 2019, researchers completed one of the largest ASD studies to date. It involved about 2 million people in five countries. Researchers concluded risk was attributed to:
- Genes. Inherited information accounts for 80% of ASD risk.
- Environment. About 20% of risk is tied to items in the environment.
- Maternal factors. About 1% of risk is tied to maternal health or choices.
The researchers were excited about this work. They said it proves that genes, which we can't control, are often at the heart of a child's autism journey.
Parents who have communication or socialization problems are more likely to have a child with ASD. If you already have a child with autism, the chances that you will have another child with ASD are increased.
But even with the high genetic component, 80% isn't 100%. Studies continually show that factors beyond genetics play a role in ASD risk.
For example, researchers examined twins. If one had ASD, the other had a 60% ASD risk. That's much higher than average, and it proves that genes do play a role. But studies like this suggest a bigger mystery.
Accepted Environmental Risks
Why do some people with autism genes develop the condition and others don't? The environment plays a role.
When researchers discuss "environment," they refer to any cause that isn't genetic. It's a massive term that incorporates dozens of factors. Only a few have been accepted as true autism risks.
In general, experts believe these four environmental factors are tied to ASD risk:
- Parental age: Multiple studies connect advanced age in fathers with ASD risk in their children. Researchers don't know why, and they can't pinpoint the exact age at which the risk rises. The view for women is more complex, experts say. Very young moms are more likely to have kids with autism than older moms. But older women can have more genetic variations in eggs than younger counterparts. That should lead to more autism cases, but researchers aren't sure about the connection yet.
- Extremely preterm birth: Twenty-six weeks of gestation seems to protect against ASD. Kids born before this point have a higher risk of autism, says Mayo Clinic.
- Infection during pregnancy: Serious infections land pregnant moms in the hospital for treatment. When that happens, researchers say, a child's risk of autism rises. But research published in 2019 sharpened the connection. Now, researchers say any infection, even a mild UTI, could enhance a child's risk of autism. An infection could trigger inflammatory proteins in the mother’s body, researchers say, or the issue could reduce a baby's access to serotonin. If a mom's body is busy fighting an infection, and that coincides with a key part of the baby's brain development, autism could occur.
- Closely spaced pregnancies: Kids conceived less than 18 months after a sibling's birth are more likely to have autism than kids who aren't. This finding from the Centers for Disease Control and Prevention can't be explained by other factors, like an underlying disorder in the pregnant woman. It's the spacing of the pregnancies that seems to matter.
You can control some of these factors. Using effective birth control for 18 months after a successful pregnancy could be a smart step, for example. And washing your hands carefully during pregnancy could keep some infections away.
But the science shows that some factors are out of your control, even though they raise the risk for your baby.
Untested but Interesting Environmental Risks
Bodies are porous, and the items we eat, drink, touch, and breathe can become part of our cells. During pregnancy, those same toxins could move through the placenta and into a baby's body.
Researchers debate how dangerous these environmental risks are in 2020, and they wonder how much ASD risk they confer. The American Speech-Language-Hearing Association says these items merit more study:
- Automotive exhaust
- Flame retardants
- Hydrocarbons (typically from water contaminated with fossil fuels)
- Polychlorinated biphenyls (found in coolants and heat transfer fluids)
It’s wise to avoid these contaminants during pregnancy. Tainted water and polluted air aren't safe for growing babies, even if they don't spark ASD.
But women who steer clear of all the items on this list may still have kids with autism. The research just isn’t clear right now.
Do Vaccines Cause Autism?
There's a lot about autism that researchers don't understand quite yet. But the science is clear on this: There is no connection between vaccines and ASD.
In 1998, The Lancet published a study connecting the measles, mumps, and rubella (MMR) vaccine with autism. It caused quite a stir, and it's still cited today by people worried about vaccines.
But as the National Capital Poison Center explains, the study is not accurate. The doctor and lead researcher falsified data. He violated accepted ethical practices and had substantial financial conflicts of interest . In time, he lost his license to practice medicine.
Moms who make decisions based on this false data are making a mistake. So are moms who avoid vaccines due to mercury exposure. The National Capitol Poison Center explains that a link between mercury in vaccines and ASD has also been debunked.
The American Academy of Pediatrics collects data on vaccines and safety. Dozens and dozens of studies prove that these interventions save lives, and they simply do not cause autism.
And yet, the association persists. Timing might play a role.
Signs and symptoms of autism emerge at about age 2, when a child is getting core vaccines. Some parents draw a causal link between the vaccine and ASD. The child had no observable signs before; they got the vaccine; and now, symptoms are noticeable.
Timing doesn't cause ASD. Vaccines aren't the issue. This is one of the things we can say for certain regarding autism risks.
Why Are Researchers Undecided on Some Issues?
If autism has been in circulation since the 1940s, and researchers have access to so many powerful tools, why can't they give clear answers about the risks in 2020? It's a complicated question to answer.
Autism experts explain that the difficulty lies in determining things that are potentially linked to autism versus those that could trigger the disorder.
Plenty of autism research relies on observation. Researchers look at two things and try to draw parallels. For example, they may ask pregnant women how often they drink coffee. Then, they follow these women and determine how many of them have kids with autism.
Unfortunately, these studies cannot prove that one thing always leads to another. Researchers find a connection, but they are not sure if it's meaningful.
Read through autism research like this, and you usually see a disclaimer that encourages more study. That means there is no definitive answer. The information is helpful to further studies, but no conclusions have been made.
For example, the National Center for Health Research cites a connection between income and ASD. In one study, for every $1,000 in income above average, the rate of autism went up by 3%.
Read this study, and you might believe wealth contributes to autism. But how does that work? How would that make sense?
Correlation is not causation. While links between autism and various other factors are interesting, they don’t mean that these factors cause autism. We still need to learn more.
Causation studies give definitive answers. Unfortunately, these studies are very hard to find with ASD.
What to Do With Research
Studies are ongoing in 2020. Researchers hope to map genes and determine what alterations lead to autism spectrum disorder. And they are searching for clear signs that toxins and environmental factors lead to autism.
It’s widely accepted that ASD likely develops due to an interplay between genes and environment. That leads to hundreds or even thousands of variables to study. This scientific work will take time. In the interim, answers are not solid.
If you're concerned about ASD risk, talk to your doctor before pregnancy. Ask about steps you can take to mitigate your risks and keep your baby healthy.
If you can, dig into your family history and ask your partner to do the same. Does someone in your family tree have autism? How many do?
While information like this can’t definitively tell you if you will have a child with autism, it can help you weigh the overall possibility. It can also be worth it to talk with a genetic counselor who can help you assess your risk.
- What Causes Autism? (January 2017). National Institutes of Health.
- Genetic Factors Are Primary Cause of Autism, Study Finds. (July 2019). UPI.
- What We Know About the Causes of Autism. Association for Science in Autism Treatment.
- The Link Between Parental Age and Autism Explained. (January 2020). Spectrum.
- Autism Spectrum Disorder. (January 2018). Mayo Clinic.
- Pregnancy Infection Increases a Child's Autism, Suicide Risk. (March 2019). UW Medicine.
- Key Findings: Autism is Associated with Amount of Time Between Births. (August 2019). Centers for Disease Control and Prevention.
- Autism. American Speech-Language-Hearing Association.
- Vaccines Do Not Cause Autism. National Capital Poison Center.
- Vaccine Safety: Examine the Evidence. (July 2018). American Academy of Pediatrics.
- Why Don't We Know Which Environmental Factors Cause Autism? (November 2015). Spectrum.
- What Causes Autism and Why Are More and More Kids Being Diagnosed With It? National Center for Health Research.