What Causes Autism Spectrum Disorder?

Many experts believe genes play the biggest role in causing autism. A 2019 study estimated that about 80% of autistic people have it due to genetics.

Research has found more than 800 genes linked to autism. Recently, researchers reported that more than 100 genes are implicated in developing autism.

While research suggests that many autistic people have small mutations in a lot of their genes, it’s not always clear how big of a role these mutations play.

In fact, many autistic people have different mutations, and some don’t show the genetic changes that are often connected to autism. This means that different mutations probably play different roles in causing autism.

For example, some mutations or combinations of mutations could:

• play a role in causing certain behaviors
• contribute to whether someone needs minimal or significant support
• increase a person’s chances of having autism

Other genetic factors that could increase someone’s chances of developing autism include:

• assigned male at birth
• having an autistic sibling
• a chromosomal condition like fragile X syndrome

Because we tend to have more control over environmental factors, researchers have put effort into studying environmental causes of autism.

So far, research suggests that the most influential factors that increase a person’s chances of developing autism are related to what happens before and during birth, like if:

• the fetus is exposed to air pollution or certain pesticides before birth
• the pregnant parent has diabetes or another immune system disorder
• the baby is born before 36 weeks old
• there were birth complications like the baby was breech, in fetal distress, or had a low birth weight
• there were any issues during birth that caused a limited amount of oxygen to the baby’s brain

These factors likely don’t cause autism by themselves. For instance, many babies are born before 36 weeks, with and without autism.

Researchers have also looked into other biological factors connected to autism. These factors are involved with:

• brain connectivity
• growth or overgrowth in certain areas of the brain
• metabolism (how the body produces energy)

Some research links certain immune system issues with autism.

The same research suggests that some infections during pregnancy could increase the child’s likelihood of having autism. Several other immune issues may also increase likelihood, including:

• problems with how the immune system works
• inflammation
• developing antibodies to a condition they haven’t been exposed to

Another possible factor linked to autism? How well an autistic person’s mitochondria (the “powerhouse” of the cell) work. Mitochondria create the majority of a cell’s energy and are an important part of metabolism, among other things.

Recent research has found that there may be a link between mitochondrial function and autism.

Additionally, scientists suggest that mitochondria are also affected by some of the same environmental factors that can increase the chances of someone being diagnosed with autism.

Other factors that may play a role in someone’s chances of developing ASD include:

• the frontal cortex of the baby’s brain overgrows shortly after birth
• the baby is male (autism is 4 times more common in boys than girls)
• advanced paternal age

An autism diagnosis may also be more likely if during pregnancy, the parent:

• had hypertension or diabetes
• experienced an antepartum hemorrhage in the third trimester or postpartum hemorrhage
• has given birth to more than 4 children
• had preeclampsia

Some people believe that vaccines cause autism. This isn’t true.

According to many organizations, including the Centers for Disease Control and Prevention (CDC), there’s no evidence that vaccines cause autism.

This belief comes from a study published in the British medical journal, Lancet, in 1998. The study concluded that the measles, mumps, and rubella (MMR) vaccine caused autism.

The study wasn’t properly conducted, and it was later retracted and disproven. But it gained a lot of publicity, and some people still believe the false findings are true.

Other factors, like smoking during pregnancy, exposure to mercury, or fertility treatments are also believed to cause autism. None of these causes have been proven.

Autism is diagnosed by a medical professional, often a pediatrician or specialist.

According to the Diagnostic and Statistical Manual of Mental Disorders (DSM-5), an autistic person must have both social and behavioral patterns that meet the criteria for autism spectrum disorder.

Someone might receive an autism diagnosis at 18 months or younger, but it’s more common to get diagnosed around 2 years old.

Still, some people don’t get a diagnosis until much older or until adulthood.

When diagnosing ASD, clinicians may look for patterns in communication like:

• difficulty with back-and-forth conversation
• differences in nonverbal communication like facial expressions or body language
• difficulty adjusting behavior to different social settings

A doctor may also look at these behavioral patterns when screening for autism:

• specific movements, actions, or gestures
• strong attachment to routine
• specific, strong interests
• differences in sensory processing

Many autistic people see autism as an identity, not as a condition to be treated. But if you’re experiencing challenges related to being autistic, there are many ways to find support, depending on your needs.

If you’re a parent of an autistic child, you can get some tips for how to support your child here. And if you’re an autistic adult, you can learn more about strategies, support, and therapies here.

When learning what kinds of resources your autistic child needs, it can help to research your options and talk to doctors. Deciding what’s best for your child will depend on the level of support they need and what’s available to you.

While there’s no single way to support autistic people, professionals often agree that the earlier you can connect with support services, the better. Many forms of support — especially for autistic children — can help them feel safe and understood.

Autism is complex. While genetics may be a key factor in causing autism, it’s likely that a person’s environment and other factors also play a role.

Researchers have found more than 800 genes linked to autism. While we still don’t know as much about environmental or biological factors, researchers have made progress.

No matter what causes autism, there’s plenty of opportunities for autistic people to live well and find the support that works for them.