Though quite a few rare genetic disorders and toxic exposures are known to cause autism (or autism-like symptoms), most cases are considered idiopathic, meaning they are without a known cause.﻿﻿ A person's biology, surroundings, and other factors may be at play—likely collectively. One postulated cause that has been disproven? Vaccinations.

Known Causes

Some researchers have found differences between brains of those with autism and others. People with autism seem to have larger brains and they also seem to process information differently.﻿﻿ In other words, their brains are "wired" differently. Research on this issue is ongoing, with intriguing findings coming out of top institutions.

Again, most of the time, autism cannot be associated with a specific cause. The few known causes of autism, which are relatively rare, include:

Depakote (also called Valproatean), an anti-seizure medication, taken during pregnancy

Fragile X syndrome (a genetic disorder)

Rubella

PKU

Tuberous sclerosis (genetic disorder)

Prader-Willi syndrome (genetic disorder)

Researchers are further exploring the connection between genetics, the environment, and autism.

Vaccines Do Not Cause Autism If your child with autism was vaccinated, this did not cause their condition. The medical community has soundly refuted these theories, though a very passionate group of parents and researchers continue to disagree based on anecdotal evidence.

Risk Factors

In addition to these rare, documented causes, some studies point to a higher risk of autism being associated with older parenthood,﻿﻿ certain types of pollution, and a variety of other issues.

Association, however, is not the same thing as causation. It may be, for example, that older parents are associated with autism because they are more likely to have autism themselves.

Additional risk factors that have been noted:

Sex: Autism spectrum disorder is four times more likely in boys than in girls.

Family history of autism

Preterm birth (before 26 weeks gestation)

In certain cases, autism may be associated with problems in the immune system. People with autism often have other physical issues related to immune deficiency.﻿﻿ The National Institutes of Health (NIH), however, states that the evidence is not yet strong enough to show a causal relationship.

There is also some evidence that children with autism are more prone to gastrointestinal (GI) problems, allergies, and food intolerances than other children, but no evidence that these cause autism.﻿﻿

Genetics

Researchers are certain that some cases of autism have a genetic basis. So, it is quite possible that genetics are involved in all cases of autism.

Many studies have shown that parents from families with autistic members are more likely to have autistic children. In addition, families with one autistic child are at increased risk of having more than one autistic child.﻿﻿

Importantly, "genetic" and "hereditary" are not the same thing. Studies have shown many cases of spontaneous genetic mutation associated with autism.﻿﻿ Spontaneous genetic mutation, as the name implies, just happens—usually for unknown reasons. In other words, a child can be born with genetic differences that are not inherited, but which may be associated with autism.

Nutrition and Autism Children with autism are often very sensitive to tastes and textures, and thus have limited diets.﻿﻿ It may be the case that they are lacking specific nutrients important to learning and social/intellectual growth. While improved nutrition may be a helpful therapy, it seems unlikely that malnutrition can cause autism.

Debunking Myths

Researchers have done a great deal of work to determine that certain things do not cause autism. Why work so hard to disprove theories? Because several related to autism have led to emotional pain, risky behaviors, health complications, and even some deaths.

For example, avoiding vaccines not only won't prevent autism, but it places your child (and other children) at risk of diseases.

Parental temperament has also been discussed as a potential cause of autism. Dr. Leo Kanner, the man who first identified autism as a unique condition, had the idea that cold, so-called “refrigerator” mothers caused autism. He was wrong.

But Dr. Kanner's thought impressed a major figure in psychology, Bruno Bettelheim. Bettelheim's book, "The Empty Fortress: Infantile Autism and the Birth of the Self," created a generation of parents who carried guilt for their child's disability. Fortunately, that burden is no longer.

As you explore the question of "what causes autism," you are likely to come across many individuals who are absolutely certain they know the answer. It's important to know, though, that the subject is highly controversial and one parent's (or researcher's) passionate statements doesn't take the place of solid research.

A Word From Verywell

You'd think that with so much information available, someone could tell you what caused autism in your child. But the odds are you'll never know; all possibilities are still under investigation. This can be, understandably, frustrating. Remember, though, that the reality is that the vast majority of parents did nothing to cause their child's autism.

Though you may not determine the cause of your child's autism, you can do a great deal to ensure that your child reaches their potential and lives the fullest and happiest life possible.