Last updated on September 25, 2026
Most autistic people are autistic because of genes inherited from their parents, according to a National Autistic Society review of 83 research papers. Published on 15 September 2026, the review draws on family studies and DNA research to explain why autism often runs in families. It also finds that no single gene determines whether someone is autistic.
The charity examined research into both genetic and other possible contributors to autism. Its conclusion is that inherited genes account for most cases, while other factors sometimes play a part, usually alongside those genes.
What the family studies found
Researchers can investigate inheritance by comparing people who share different amounts of DNA. If a characteristic occurs more often among close relatives than distant relatives, and more often among identical twins than non-identical twins, that provides evidence of genetic influence.
A study of more than two million people across five countries found 22,156 people with an autism diagnosis. Published in JAMA Psychiatry in 2019, it estimated that inherited genetic factors accounted for about 80% of the variation in autism likelihood across the populations studied. The researchers found little evidence of an additional effect attributable specifically to the mother.
That 80% is a population estimate. It isn’t a prediction for an individual child, and it doesn’t mean that 80% of one person’s autism came from their genes.
A UK study of twins reached a similar conclusion through a different method. Across several measures of autism, identical twins were considerably more alike than non-identical twins. The researchers’ estimates of genetic influence ranged from 56% to 95%, depending on how autism was measured.
Autism also becomes more likely as family members share more genes. In a study covering births in six countries and regions, researchers examined more than 2.5 million children. They found that a child with an older autistic sibling was 8.4 times as likely to receive an autism diagnosis as a child without an autistic family member. Having an autistic cousin was associated with roughly twice the likelihood. These are relative comparisons between groups, rather than the chance of a diagnosis for any particular family.
What DNA research adds
Family studies establish a strong pattern of inheritance. DNA research investigates which genetic differences contribute to it. The answer is spread across many parts of the genome.
Some differences linked to autism are common in the wider population and each contributes a small amount. A 2014 study published in Nature Genetics found that these common differences, considered together, accounted for much of the genetic contribution in the population it studied.
Other differences are rare and can have a larger effect. Some are inherited; others arise for the first time in a child. A large sequencing study published in Cell analysed DNA from 35,584 people, including 11,986 autistic people. It identified 102 genes associated with autism risk. Many of those genes are active early in brain development and have roles in regulating gene activity or communication between nerve cells.
The studies examine different parts of the same picture. Common genetic differences can collectively have a substantial effect across a population, while a rare variant may be particularly relevant to an individual person. Neither type provides a universal explanation for autism.
This also helps explain why autism doesn’t follow a simple family pattern. An autistic person may have non-autistic parents, while two autistic relatives may have quite different characteristics. The Society’s guide to the causes of autism discusses these questions in more detail.
Why there’s no genetic test for autism
Scientists have identified genes associated with autism, but that doesn’t give clinicians a DNA result that can confirm or rule out a diagnosis. The combinations involved vary between people, and carrying a particular genetic difference doesn’t automatically mean someone will be autistic.
Genetic testing can sometimes identify a separate condition relevant to a person’s health or development. It can’t diagnose autism or reliably predict whether a child will be autistic, according to the Society. NHS England’s guidance on assessment likewise states that there’s no biological test or scan used to confirm or refute an autism diagnosis. Assessment instead considers a person’s development and characteristics.
How autistic people responded
The National Autistic Society shared its review with a panel of 300 autistic people and family members. Almost two thirds, 64%, felt the information could help dispel myths about autism’s causes. Some were concerned that discussing inherited genes might lead parents to feel blamed.
Kelly-Marie, from Birmingham, told the charity that recognising autism among her siblings and children helped her understand their shared experiences. “It can be a relief that nobody has done anything ‘wrong’,” she said.
Panel members also told the Society they’d prefer future research to address priorities identified by autistic people and their families, rather than focus on finding a “cure”. The charity has included responses to their questions in its published guidance.
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