Same Switches, Different Conditions: 683 Genetic Variants That Connect Autism, ADHD, and Six Other Psychiatric Disorders
“Why does my child have both autism and ADHD?” It is one of the questions I hear most often in clinic. Close behind it: “My son has autism, my daughter has anxiety, and my husband was diagnosed with ADHD last year. Is that a coincidence?”
The short answer is: almost certainly not. And a new study has given us the most detailed molecular explanation yet for why different conditions cluster in the same families.
Not genes, but switches
Most of the genetics research you read about focuses on coding variants, changes in the parts of DNA that carry the instructions for building proteins. But the human genome is vast, and only about 2 percent of it codes for proteins. The rest, far from being “junk DNA” as it was once dismissively called, contains an enormous regulatory layer: sequences that control when, where, and how much each gene is switched on.
Researchers at the University of North Carolina tested approximately 18,000 genetic variants associated with eight psychiatric conditions: autism, ADHD, schizophrenia, bipolar disorder, depression, Tourette syndrome, OCD, and anorexia. They found 683 variants that significantly alter gene regulation. These are not changes in genes themselves. They are changes in the switches that control those genes.
Same switches, different positions
The key insight is this: the same regulatory switches, in different configurations, appear to produce different clinical outcomes. This helps explain a pattern that has baffled clinicians and families alike. Why does autism run alongside ADHD in one family, alongside anxiety in another, and alongside mood disorders in a third? The answer, increasingly, is that these conditions share regulatory architecture. The same switches, dialled differently, produce different conditions.
This also helps explain why the same medication can sometimes help across diagnostic boundaries. Stimulants prescribed for ADHD sometimes improve executive function in autistic individuals. SSRIs prescribed for depression sometimes help with anxiety in autistic adults. If the underlying regulatory biology overlaps, it makes sense that pharmacological interventions would cross diagnostic lines too.
What co-occurrence really means
For families, this finding reframes co-occurrence. Having a child with both autism and ADHD is not bad luck, and it is not misdiagnosis. It reflects shared regulatory biology. The variants that influence your child’s autism and their ADHD may literally be the same variants, acting on the same switches, producing effects that we currently split into separate diagnostic categories.
If different conditions run in your family, this is a genetic explanation, not a coincidence. And it supports what many families have long felt: that the diagnostic labels, while useful for accessing services, do not always capture what is actually going on biologically.
Where this leads
The practical implication is a move toward what researchers call transdiagnostic approaches: understanding and treating the underlying biology rather than the diagnostic label. If autism, ADHD, and anxiety share regulatory variants, perhaps we should be thinking less about which box a child fits into and more about which biological pathways are affected and what we can do about them.
We are not there yet. Diagnostic categories remain essential for research, for clinical communication, and for accessing support. But the direction of travel is clear, and studies like this one are part of the reason why.
References
- UNC Neuroscience research: 683 regulatory variants across 8 psychiatric disorders. Related: Psychiatric Genomics Consortium cross-disorder analyses.
Dr Odet Aszkenasy is a Consultant Community Paediatrician and the author of The Genetics of Autism: A Guide for Parents and Professionals.