Genetic clues point to broader diagnoses in autism, ADHD

polygenic risk – A study of 140,000 people in Denmark finds that people diagnosed more recently with ADHD or autism carry fewer ADHD- and autism-linked genetic variations than those diagnosed a decade earlier. The pattern points toward a broadening of diagnostic criteria as a

The question has been asked for years, especially by families watching rates climb: Are autism and ADHD being diagnosed too often, or are we finally seeing what was always there?

A new genetic look at thousands of Danish lives pushes the debate toward one answer—at least in part. In a study spanning 140. 000 people. researchers found that those diagnosed with ADHD or autism in more recent years have fewer genetic variations linked to these conditions than people diagnosed a decade earlier.

Diagnoses of autism and ADHD have risen dramatically across the world over the past two decades, reaching up to tenfold. The increase has been especially visible among girls and adults. Explanations have ranged from better awareness and less stigma to changes in the diagnostic criteria themselves. Other theories have pointed to the commercial interests of pharmaceutical companies and private diagnostic clinics. Still others have blamed the environment. including rising screen use and claims—often disputed—that childhood vaccinations and prenatal exposure to paracetamol (acetaminophen) contribute to risk.

Genetics is central to the latest study. ADHD and autism are highly heritable. and research has identified thousands of common gene variants—each one associated with a slightly higher likelihood of developing core traits. In recent years. advances in DNA analysis have made it possible to calculate a person’s “polygenic risk score.” A high score for ADHD or autism. however. is “not diagnostic in itself. ” as Sonja LaBianca of Copenhagen University Hospital in Denmark put it. Such scores do not capture the effects of environmental, cultural and social factors, or the impact of rare genetic variants.

But because DNA in a population doesn’t shift much over a decade, those scores can help set a baseline and test which forces are most likely moving the numbers.

LaBianca and colleagues built polygenic risk scores for autism and ADHD using genome-wide association studies published in 2018 and 2019. They applied those scores to participants from the iPSYCH cohort study: 140. 000 people overall. including 37. 000 who had been diagnosed with ADHD or autism between 1994 and 2016. The researchers didn’t stop there. They also calculated polygenic risk scores for depression and for certain personality traits—such as risk-taking—that are associated with mental health conditions.

With that data, the team tested three possible scenarios for why diagnosis rates have risen. One scenario is straightforward: broadening diagnostic categories lowered the threshold for diagnosis. Another is that people who used to be diagnosed with mental health conditions are now being recognized as neurodivergent instead. A third is that improved awareness helps clinicians and families spot people who previously “fell through the gaps.”.

The pattern the researchers found is hard to ignore. People diagnosed more recently had significantly lower polygenic risk scores for ADHD and autism than those diagnosed earlier. They also had lower risk scores for mental health conditions and for personality traits linked to conditions like ADHD. including impulsivity.

That combination. LaBianca said. points to a key explanation: the diagnostic system is probably not catching only the people with the most obvious traits—the ones who also tend to have the highest polygenic risk scores. Instead, more diagnoses appear to be reaching individuals whose genetics place them lower on the ADHD- and autism-associated spectrum.

Better awareness and reduced stigma may still play a role, but the study has “less data to support that,” LaBianca said.

Some readers may hear the findings and jump to the charge of overdiagnosis. LaBianca cautioned against that leap. Even the group with the lowest polygenic scores still had significantly more risk variants than a neurotypical control group. “That supports the finding that we’re not overdiagnosing,” she said. She added that she would use the term “overdiagnosing” only if clinicians were diagnosing individuals at the same polygenic level as the background population.

Tinca Polderman at Vrije University Amsterdam in the Netherlands agreed that broadening diagnostic criteria is likely a major driver. But she warned against separating genetics and environment as if they were independent levers. “Polygenic risk scores provide just a piece of the puzzle,” she said.

Her point landed with particular weight on what comes next: if more individuals are seeking help for these symptoms while carrying less genetic predisposition. researchers will need to search harder for other risks beyond DNA. “If more individuals are seeking help for these symptoms. but are less genetically predisposed. we need to look at other risk factors. ” LaBianca said.

autism ADHD diagnoses polygenic risk scores genetics Denmark iPSYCH cohort diagnostic criteria neurodivergent impulsivity