Features of autism can affect age of diagnosis – and so can genes

The age at which a person is diagnosed with autism is sometimes linked to their genetic make-up and their risk of developing mental-health conditions, according to an analysis of behavioural and genetic data¹. Children who are diagnosed early — typically before six years old — are more likely to experience social and behavioral challenges during infancy and early childhood, whereas those who are diagnosed later experience higher rates of conditions such as attention deficit hyperactivity disorder (ADHD) and depression.

Differences in genetic profiles seem to account for about 11% of this distinction. The findings, published today in Nature, counter previous assumptions that later diagnoses mainly occurr in children who exhibit milder autistic traits overall, or experience delays in diagnosis owing to social factors, such as access to health care, says Varun Warrier, who studies neurodevelopment at the University of Cambridge, UK, and is a lead author on the study.

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But the results do not mean that autistic people fall neatly into two categories, he adds. “What we are looking at are the averages underlying these groups,” he says. And the age at diagnosis is still only an imperfect proxy for the developmental and genetic differences the study found: factors such as delays in accessing health care can still exert a big effect.

The findings could spark further research to improve diagnoses and better personalize support for autistic people, Warrier adds. “The more you understand about a condition and what gives rise to the risk for it, the better your understanding of how to diagnose it and how to treat it,” says Elliot Tucker-Drob, who studies developmental psychology at the University of Texas at Austin.

No single cause

Autism is a complex condition that affects brain development and can cause repetitive behaviours and difficulties with social communication. There is no single cause of autism. Last week, US health secretary Robert F. Kennedy Jr called the search for genetic drivers of the condition “entirely fruitless”, but, in fact, researchers have found the heritabilty of autism to be about 80%.

Those genetic factors, and the traits that they influence, are extraordinarily diverse. “It’s been such a challenge to really parse the genetics of autism,” says Natalie Sauerwald, who studies genomics at the Flatiron Institute in New York City. In one study published this year, for example, Sauerwald and her colleagues incorporated data on nearly 240 characteristics of autism, including behavioural traits². “It’s not exactly a two-question questionnaire,” she says.

Diagnostic patterns

Warrier’s research into this complexity began with a simple question: why are some children diagnosed with autism at a young age, and others diagnosed later, sometimes well into adolescence or beyond?

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This has often been attributed to social factors, such as cultural stigmas around autism or a lack of access to care, that delays diagnosis, says Warrier. Another explanation has been that early diagnoses might occur in people whose autistic traits are more pronounced, whereas later diagnoses could reflect milder challenges that are not noticed as quickly.