Genetic study: Late autism diagnosis linked to risk of mental disorders
The timing of an autism diagnosis matters. A new study from Aarhus University and collaborators points to genetic and developmental differences between those diagnosed early and those diagnosed later in life.
New research challenges the idea that autism is a single, unified condition with one common underlying cause.
An international study involving researchers from Aarhus University shows that autism diagnosed in early childhood has a different genetic and developmental profile compared to autism diagnosed in late childhood or later.
“This is the first time a genetic study has focused on the time of diagnosis. Through this, we’ve identified distinct genetic profiles linked to two typical developmental trajectories followed by autistic children,” says Professor Anders Børglum from the Department of Biomedicine at Aarhus University.
One of the two trajectories identified by the researchers is associated with early diagnosis and, for example, communication difficulties in very young children. The other is associated with later diagnosis, increased social and behavioral challenges in adolescence, and a higher genetic predisposition for conditions such as ADHD, depression, and PTSD.
Significant differences in genetic profiles
The study, recently published in the scientific journal Nature, analyzed behavioral and genetic data from several large cohorts in Europe and the USA.
Researchers found that children diagnosed with autism early in life—typically before age six—more often exhibited behavioral challenges in early childhood, such as difficulties with social interaction.
In contrast, individuals diagnosed in late childhood or later were more likely to experience social and behavioral difficulties during adolescence. They also had a higher risk of developing mental disorders such as depression and PTSD.
The researchers then compared the genetic profiles of early- and late-diagnosed autism with those associated with other developmental and psychiatric conditions. This revealed significant differences: the average genetic profile of late-diagnosed autism more closely resembles that seen in ADHD, depression, and PTSD than in early-diagnosed autism.
Study highlights distinct developmental trajectories
“This study is a step toward understanding how autistic traits emerge - not just in early childhood, but also later in life,” says Professor Jakob Grove from the Department of Biomedicine at Aarhus University, who also contributed to the study.
He emphasizes that it's not surprising that different individuals with autism follow different developmental paths - nor that their genetic architecture varies.
“But the way in which these genetic architectures differ is unexpected. What’s particularly surprising is that those diagnosed later actually have more genetic overlap with conditions like ADHD, depression, and PTSD than with early-diagnosed autistic people,” he says.
“Before this study, one might assume that late-diagnosed individuals develop comorbidities simply because they’ve struggled without support and received their diagnosis late. Now we can see that they are, to some extent, genetically predisposed to these challenges,” adds Jakob Grove.
Interaction of factors leads to poorer mental health
The study was led by researchers from the University of Cambridge. The authors stress that a lack of early support may also contribute to the increased risk of mental health issues among those diagnosed later.
It’s also important to note that these findings reflect average differences across a spectrum - early’ and ‘late’ diagnosed autism are not formal diagnostic categories.
The study investigated so-called polygenic factors - a set of thousands of genetic variants that collectively influence certain traits. Researchers found that commonly inherited polygenic factors explain about 11 percent of the variation in age at autism diagnosis.
A key next step will be to understand the complex interaction between genetic and social factors that contribute to poorer mental health among people with a late autism diagnosis.
Contact
Professor Anders Børglum
Aarhus University, Department of Biomedicine
Phone: +45 60 20 27 20
Email: anders@biomed.au.dk
Professor Jakob Grove
Aarhus Universitet, Department of Biomedicine
Phone: +45 29 80 17 68
Email: grove@biomed.au.dk
Behind the Research Findings
- The study is a genetic investigation of common DNA variants across the entire genome in thousands of individuals (GWAS) and examines the genetic overlap between different developmental and psychiatric diagnoses.
- Collaborators: University of Cambridge, The Psychiatric Genomics Consortium (PGC), University of Bristol, and iPSYCH
- External funding: Wellcome Trust, Lundbeck Foundation, EU Horizon Europe
- Read more in the scientific article: https://www.nature.com/articles/s41586-025-09542-6