Autism genetics: is autism genetic?

If you have recently recognized autistic traits in yourself, you may have started noticing them in a parent, sibling or child too. That is common, and it reflects one of the most consistent findings in autism research: autism runs in families, mostly because of genes. This page explains what that means, and what it does not.

Is autism hereditary? What twin studies show

Twin studies compare identical twins, who share nearly all their genes, with non-identical twins, who share about half. If identical twins are much more often both autistic than non-identical twins, genes are playing a large part. That is exactly the pattern researchers find.

What heritability means, and what it does not

Heritability is a population statistic. A figure of 80 percent means that about 80 percent of the variation in autism across a population is linked to genetic differences between people. It does not mean that 80 percent of a single person's autism comes from genes, and it does not mean an autistic parent has an 80 percent chance of an autistic child. Those are common misreadings.

How many genes are involved?

There is no single "autism gene". Research points to a very large number of genetic differences that each nudge development a little, plus a smaller number of rarer variants with larger effects.

• Common variants: small differences shared by many people. Individually each has a tiny effect, but together they add up. A 2019 genome-wide study of 18,381 autistic people and 27,969 comparison participants identified the first five clearly linked locations in the genome and showed that common variants contribute substantially.
• Rare variants: less common changes, some inherited and some new in the child (called de novo). A 2020 sequencing study of 35,584 people, 11,986 of them autistic, identified 102 genes linked to autism, many involved in how brain cells develop and communicate.
• Overlap with other traits: the 2019 study found that the genetic background of autism overlaps with that of several other traits and conditions, including educational attainment, schizophrenia and major depression. Overlap means shared genetic influences, not that one condition leads to another.

Does autism come from the mother or the father?

From either, and usually from both. Most of the genetic contribution comes from many common variants that each parent passes on, mixed together in the child. Neither parent is "the source". Large population studies have also tested whether something specific about the mother's body or pregnancy explains autism in families, and found that effect to be very small.

Can autism be passed down?

Yes, in the sense that it often runs in families. Autistic adults frequently recognize traits in parents, grandparents or siblings who were never diagnosed, especially in generations when autism was rarely identified in adults. But inheritance is not simple. Two autistic parents can have a child who is not autistic, and two parents with no obvious traits can have an autistic child. Genetic counseling can help families who want to understand their situation, but no one can predict a specific child's outcome with certainty.

What about the environment?

Genes do not explain everything. The WHO lists several environmental factors that appear more often in the backgrounds of autistic children, such as older parental age and some exposures during pregnancy. These are associations studied at a population level, and none is a cause on its own. Vaccines, diet after birth and parenting style are not among the established factors.

• Autism myths and factsCommon autism myths checked against research: vaccines, empathy, parenting, "everyone is a little autistic", gender, work and relationships, all sourced.

Is there a genetic test for autism?

No genetic test can diagnose autism, in children or adults. Autism is diagnosed through a clinical assessment of development, communication and behavior. Genetic testing is sometimes offered to children, usually to look for a known genetic condition that can occur alongside autism and may have medical implications, not to confirm autism itself.

• How to get tested for autism as an adultYes, adults can be tested for autism. The practical steps: preparing notes, getting a referral, choosing an assessor, paying, and what the result means.

Why genetic research is sensitive

Many autistic people are wary of genetic research, worried it could be used to screen autistic people out of existence. Researchers and autistic advocates have argued that genetics should be used to understand autism and co-occurring medical conditions and to improve support, not to judge whose lives are worth living. We share that view: understanding where autism comes from is useful because it can reduce blame and improve care.