When my child was first diagnosed with autism, my head immediately started spinning. One of the first things I thought about was, where did her autism come from? Was it genetic? Did it come from my side of the family or her father's? And perhaps one of the hardest questions: Was there something that I did to cause it?
It's natural for parents to look for an explanation, but autism genetics isn't as simple as tracing a condition through your family tree. There's no single autism gene, and having no family history of autism doesn't mean that genetics aren't involved.
Research shows that autism is highly heritable. However, heritable doesn't mean inevitable. It also doesn't mean that one parent caused or directly passed autism to their child.
Understanding that difference can make the genetics much less confusing. It can also help take some of the unnecessary blame off parents.
Key Takeaways
- Autism is highly heritable, meaning genetic differences explain much of the variation in autism across a population.
- Heritability does not tell you what percentage of your child's autism came from genetics.
- Autism usually cannot be traced to one parent or a single “autism gene.”
- A younger sibling of an autistic child has a higher chance of also being autistic, but heritability and sibling recurrence are different statistics.
- Genetic testing may identify a genetic finding in some children, but it cannot explain every case of autism. If you have questions about your child’s development, you can get started with Alpaca Health.
Is autism hereditary?
Yes, genetics do play a role in autism, but autism isn't usually inherited in a simple or predictable way.
Researchers have identified many genetic differences associated with autism. Some are inherited from a parent, while others arise as a new genetic change in a child. Many genetic factors can contribute, rather than one change being solely responsible.
One large Swedish study analyzed millions of sibling pairs and estimated the heritability of autism at 83%. That number may seem straightforward, but it's easy to misunderstand. It does not mean that 83% of autistic children inherited autism from their parents. It also does not mean that 83% of your child's autism came from their genetics.
It's best to look at heritability as a statistic researchers use to describe differences across a population. That's also why knowing that autism is highly heritable doesn't tell an individual parent whether or not a child will be autistic. We'll look at sibling chances separately below.
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What a heritability percentage does and does not tell you
Heritability means how much of the variation in a trait across a population is associated with genetic differences. It doesn't divide an individual child's autism into genetic and environmental percentages.
That's an important distinction when you read statements online such as “autism is 80% genetic.”
In 2017, a Sandin study estimated autism heritability at 83%. However, earlier studies using the same underlying Swedish data produced an estimate of only about 50%. The difference came partly from how researchers defined and analyzed sibling pairs, not because autism suddenly became more genetic.
This helps explain why you may see different heritability percentages online.
It's best to think of heritability as a population statistic and not a percentage assigned to your child. An 83% heritability estimate doesn't mean your child's autism is 83% due to genetics and 17% due to the environment.
It doesn't tell you which parent contributed more, whether another child will be autistic, or whether a specific genetic change caused your child's autism. Those are different questions that require different types of research.
Which parent does autism come from?
The genetics of autism are complex. Many genetic differences can contribute to whether a child is autistic. However, autism doesn't usually come from a single parent.
Researchers have looked at whether a parent's age affects the likelihood of having an autistic child. A large international study of more than 5.7 million children found that the ages of both the mother and father are associated with differences in autism likelihood.
But these findings still don't tell us that autism comes from the mother or the father.
What the research shows about the father’s contribution
The study found that children born to fathers aged 50 or older were about 1.66 times more likely to have autism than children born to fathers between 20 and 29 years of age.
Saying “1.66 times more likely” can make the difference sound larger than it is. In absolute terms, it's roughly a change from about 3 in 100 children to about 5 in 100.
Paternal age is one factor researchers have studied. However, it can't tell you why an individual child is autistic.
What the research shows about the mother’s contribution
Research has also found an association between autism and maternal age. The same study found that mothers aged 40 to 49 had a modestly higher likelihood of having an autistic child compared with mothers aged 20 to 29. Mothers younger than 20 also had a modest increase in likelihood.
Again, these are population-level associations, and they don't mean a mother's age caused her child's autism. There isn't a test or family history that can simply point to a parent and say, "This is where autism came from."
How can autism be genetic when no one else in the family is autistic?
It's possible for an autistic child to have no family history of autism. There are a couple of reasons why.
New genetic changes that neither parent carried
Some genetic differences occur for the first time in the child. These are called de novo genetic changes, meaning they're present in the child but not inherited from either parent.
A 2014 study examined more than 2,500 families with an autistic child and estimated that de novo coding mutations contributed to about 30% of autism diagnoses in these simplex families.
This doesn't mean new genetic changes cause 30% of all autism. The study looked at families where one child was autistic and other family members were not.
Family traits that were never given a diagnosis
Genetics can run through a family without a relative meeting all the criteria for autism. You may recognize certain traits in yourself or even other relatives only after your child is diagnosed.
Maybe someone in the family has always needed predictable routines, had strong sensory preferences, or found social situations difficult.
Having a single trait or multiple traits doesn't mean that person is autistic. However, it does help explain why “no autism diagnosis in our family” isn't the same as “no genetic contribution in our family.”
If one child is autistic, what are the chances a sibling will be?
A 2024 study followed 1,605 infants who had an older autistic sibling until the age of three. Researchers found that 20.2% of the infants were also diagnosed with autism, or about 1 in 5.
That tells us that a younger sibling of an autistic child has a higher chance of also being autistic. However, most younger siblings in the largest recent study were not diagnosed with autism.
The likelihood wasn't the same for every family. The data showed that recurrence was higher when:
- The younger sibling was a boy
- The family already had more than one autistic child
- The older autistic sibling was a girl
The study found that 25.3% of younger boys were diagnosed, compared with 13.1% of younger girls. Also, families with more than one older autistic child had a higher recurrence than families with one.
Heritability and sibling recurrence are not the same. The 83% figure describes how genetic differences contribute to variation in autism across a population. The 20.2% figure answers a much more concrete family question: among the younger siblings followed in this study who already had an autistic sibling, how many were later diagnosed with autism?
Neither of these statistics can predict with certainty whether your child will be autistic.
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What researchers mean when they say environmental factors
Researchers also study possible environmental influences on autism, meaning non-genetic factors that may be associated with a diagnosis. An association doesn't necessarily mean that something caused autism.
Taking acetaminophen during pregnancy is a good example. A few studies have reported an association between prenatal acetaminophen use and autism. This has raised understandable concerns among parents, but research findings need to be interpreted carefully.
A 2024 study followed nearly 2.5 million children and found a small association between acetaminophen use during pregnancy and autism. But when researchers compared siblings to better account for genetic and family factors, the association disappeared.
So the researchers concluded that the earlier association may have been explained by shared family factors rather than acetaminophen itself.
For us as parents, that's an important distinction. A study showing that two things occur together doesn't prove that a medication you took, a food you ate, or another choice you made during pregnancy caused your child's autism.
Which non-genetic factors have consistent evidence behind them
Some factors, including parental age and certain pregnancy or birth-related factors, have shown more consistent associations with autism. But even these findings can't explain why an individual child is autistic or prove that one factor caused it.
Why some reported links disappear under closer study
Researchers use different study designs to determine whether an apparent association is likely to represent cause and effect. Sibling comparisons can be particularly useful since siblings share many genetic and family factors.
The acetaminophen study shows how much that matters. What initially looked like a small association across the broader population was no longer present when researchers dug deeper and compared siblings.
Research on autism continues to evolve. Parents shouldn't interpret every reported association as evidence that a decision they made caused their child's autism.
Did something you do cause your child’s autism?
There usually isn't one thing a parent did or didn't do that explains why their child is autistic.
Unfortunately, parents have been blamed for autism before, often without good evidence. In the mid-20th century, the “refrigerator mother” theory blamed autism on mothers who supposedly were not emotionally warm enough with their children. That has been discredited, and the idea was wrong.
Research has also looked at vaccines. A 2019 nationwide study of 657,461 Danish children found no evidence of an increased autism risk after MMR vaccination, including among children with an autistic sibling.
Autism genetics are complex, and science often cannot tell a family exactly why one child is autistic. Not having a simple explanation does not mean a parent's choices caused it.
What can a genetic evaluation tell your family, and what can it not?
A genetic evaluation may help identify a genetic condition or change associated with your child's autism. A geneticist will typically review your child's medical, developmental, and family history before determining whether testing may be appropriate.
Chromosomal microarray is one type of genetic test that looks for missing or extra pieces of genetic material.
Genetic testing may provide information about other health considerations or the chance that a genetic condition could occur in other family members. However, testing alone doesn't find an explanation for every autistic child. A negative result also doesn't mean genetics aren't involved.
Genetic testing can't predict your child's future abilities, support needs, or level of independence.
Alpaca Health does not provide genetic counseling or genetic testing. If you have questions about genetics, ask your child's pediatrician or healthcare professional whether a referral to clinical genetics or a genetic counselor may be appropriate.
What knowing the genetics changes for your family right now
It's natural to look for an explanation. However, finding one doesn't change who your child is or what they need today. Your child's support will still be based on their individual strengths, challenges, and daily needs.
That's why a specific genetic finding isn't required to benefit from appropriate developmental, educational, or therapeutic support.
How Alpaca Health helps families asking whether autism is hereditary
Alpaca Health doesn't provide genetic counseling or testing. We can help families take the next step when they have questions about their child's development or possible autism.
Alpaca Health provides autism evaluations and individualized ABA therapy for families when needed. Get started with Alpaca Health to explore your family's next steps.
You don't have to figure this out alone.
Alpaca Health matches your family with a vetted, in-network BCBA, often within days and with no waitlist. We handle the insurance paperwork so you can focus on your child.
Get matched with a BCBA →Frequently asked questions about inheriting autism
Is autism dominant or recessive?
Autism is usually neither dominant nor recessive. It generally doesn't follow one simple dominant or recessive inheritance pattern. Several different genetic factors can contribute, but some genetic conditions associated with autism have specific inheritance patterns.
Can autism skip a generation?
It's possible for autism to appear in a child even when neither parent has an autism diagnosis. Genetic differences may be inherited without every family member being autistic, and new genetic changes can also occur.
Is high-functioning autism hereditary?
“High-functioning autism” isn't a specific diagnosis or a genetic type of autism. Autism is highly heritable, but science doesn't divide its genetics into functioning labels.
What are the three main causes of autism?
There are not three established causes of autism. We know genetics play a major role, but researchers continue to study non-genetic influences and how they may interact with genetic factors. If you want to move from questions about cause to a plan for support, you can start an intake.
