The Categories Are Ours. The Biology Doesn't Care.
Psychiatry sorts the mind into neat boxes: autism here, ADHD there, depression, bipolar, schizophrenia, OCD, Tourette, anorexia. But these conditions cluster in families and pile up in the same person far more often than chance would predict. Why?
A 2025 study from the University of North Carolina, published in Cell, gives the clearest molecular answer yet: many of the genes involved don't respect our diagnostic borders at all.
The Study: Testing Genes in Living Cells
Instead of just reading DNA, the UNC team (Hyejung Won lab) did something more direct. They took 17,841 genetic variants from 136 genomic "hotspots" linked to psychiatric conditions and inserted them into living human neural cells, using a technique called a massively parallel reporter assay.
This let them watch which variants actually changed gene regulation - not just which ones correlate statistically, but which ones do something.
The result: 683 of the 17,841 variants had a real, measurable effect on how genes are switched on and off in developing neurons.
Eight Disorders, One Shared Genetic Layer
These 683 functional variants span eight conditions:
- Autism spectrum disorder
- ADHD
- Major depression
- Bipolar disorder
- Schizophrenia
- Obsessive-compulsive disorder (OCD)
- Tourette syndrome
- Anorexia nervosa
The same variants influence multiple disorders. The biological machinery underneath is shared - even when the clinical labels look completely different.
The Key Discovery: Shared Genes Work Harder and Longer
The researchers split the 683 variants into two groups:
- Pleiotropic variants - shared across multiple disorders.
- Disorder-specific variants - tied to a single condition.
The pleiotropic (shared) variants were more active, more sensitive to change, and active for much longer during brain development than the disorder-specific ones.
In other words, the genes that touch many conditions at once are precisely the ones doing the heaviest lifting during the brain's formative windows. That is a profound clue about where these conditions actually originate.
Why This Matters For How We Think About the Mind
This reframes mental health in a way that matches what many neurodivergent people already experience:
- Co-occurrence isn't a coincidence. If you have autism and anxiety, ADHD and depression, OCD and tics - that overlap has a molecular basis, not a character flaw.
- Diagnostic boxes are tools, not truths. They help clinicians communicate, but your brain was built by shared genetic programs that never read the DSM.
- It opens the door to universal therapies - treatments targeting the shared root mechanisms rather than each label separately.
An Honest Caveat
Shared genetics does not mean "the same genes cause everything." It means partial overlap - a common genetic layer beneath conditions that still have their own specific components and their own lived realities. These variants also affect risk and regulation; they are not switches that determine a destiny.
This is early-stage functional genomics, powerful but still being extended. The value isn't a treatment tomorrow - it's a more accurate map of where these conditions come from.
The Bottom Line
Nearly one billion people worldwide live with a mental health condition. This research suggests that under the hood, many of those conditions share far more than we assumed. Understanding your own profile - across the categories, not just within one - is where personalized care begins.
Source: Deng et al., Won H (2025). Massively parallel reporter assay investigates shared genetic variants of eight psychiatric disorders. Cell. DOI: 10.1016/j.cell.2024.12.022 (UNC).