New work on thousands of gene variants suggests that autism, ADHD, depression and several other diagnoses may be different outcomes of overlapping genetic programs active during brain development.
A single genetic thread running through eight conditions
A US research team has reported that eight major psychiatric disorders appear to share a substantial slice of their genetic makeup.
The conditions examined were:
- Autism spectrum disorder
- Attention deficit hyperactivity disorder (ADHD)
- Schizophrenia
- Bipolar disorder
- Major depressive disorder
- Tourette syndrome
- Obsessive-compulsive disorder (OCD)
- Anorexia nervosa
Researchers had already known, from a large 2019 analysis, that 109 genes were implicated in different combinations across these eight conditions.
The new study, published in early 2025 in the journal Cell, goes several steps further.
Instead of just listing genes, the team tracked how specific variants of those genes behave during brain development, and how they might steer brain cells down different paths.
Many of the shared variants remain active for long stretches of brain development, influencing several stages rather than a single moment in time.
How the team probed the brain’s genetic control panel
The scientists, led by geneticist Hyejung Won at the University of North Carolina, started with nearly 18,000 DNA variants linked to the eight conditions.
These variants were divided into two broad groups: those shared across multiple disorders, and those unique to a single diagnosis.
To see what these variants actually do, the team inserted them into precursor cells that later develop into neurons.
These precursor cells act as a kind of rehearsal stage for the future brain, where early instructions are laid down.
By watching changes in gene activity inside these cells, the researchers could pinpoint variants that genuinely alter how genes switch on and off.
This approach allowed them to identify 683 specific variants that clearly affected gene regulation.
They then examined these variants further in developing mouse neurons, providing a second line of evidence in a living brain.
What “pleiotropy” means for mental health
A core concept in this work is pleiotropy: when a single gene variant influences more than one trait or condition.
Many of the variants linked to multiple psychiatric diagnoses turned out to be strongly pleiotropic, nudging several brain processes at once.
In simple terms, the same small change in DNA can raise the chance of autism in one person, ADHD in another, and depression in a third, depending on how it interacts with other genes and life experiences.
The researchers found that these pleiotropic variants:
- Engaged in many more protein-to-protein interactions than variants unique to one condition.
- Were active in a broader range of brain cell types.
- Participated in regulatory mechanisms that act at multiple stages of brain development.
The findings hint at a core set of genetic switches that sit high up in the brain’s control hierarchy.
Changes at that level can ripple down through networks of proteins and genes, contributing to different clinical pictures.
Why diagnoses often cluster together
The shared genetic architecture may help clarify why psychiatry often sees overlapping diagnoses rather than neat boxes.
Autism and ADHD, for instance, show particularly high overlap: up to 70 percent of people diagnosed with one also meet criteria for the other.
Families frequently show clusters of different conditions, such as depression in one relative, bipolar disorder in another, and OCD in a third.
A common set of genetic variants, active across multiple brain cell types and stages, offers a plausible explanation for these family patterns.
This doesn’t mean that the conditions are identical, or that environment and life events do not matter.
Each disorder still carries its own unique genetic contributions and is shaped by upbringing, stress, trauma, infections, and many other influences.
But there now appears to be a shared biological backbone underneath that variety.
From genetic tangle to treatment targets
Pleiotropy used to be seen mainly as a nuisance for researchers.
If the same genes contribute to several disorders, then drawing clean diagnostic lines from biology alone becomes extremely difficult.
Won argues that this challenge can be turned into an opportunity.
If scientists can map the shared genetic factors that sit at the crossroads of several conditions, pharmaceutical research may be able to design treatments that benefit more than one diagnosis at a time.
For example, if a particular protein network is influenced by pleiotropic variants in autism, ADHD and bipolar disorder, a drug that stabilises that network could in theory ease symptoms across all three.
Current psychiatric medications are often blunt tools, developed decades ago and used across conditions without a clear genetic rationale.
Targeting shared genetic pathways could eventually create more precise, mechanism-based treatments.
A vast potential impact
The World Health Organization estimates that around one in eight people worldwide lives with a psychiatric condition.
That equates to almost one billion individuals.
Even a modest improvement in treatments, especially therapies that help multiple diagnoses, could affect huge numbers of patients and families.
| Global burden | Approximate figure |
|---|---|
| People living with psychiatric conditions | ~1 billion (1 in 8) |
| Core genes linked to 8 disorders (2019 study) | 109 genes |
| Variants tested in precursor cells | ~18,000 variants |
| Variants confirmed to affect regulation | 683 variants |
What this does and does not mean for individuals
Although the study focuses on shared genetic roots, it does not suggest that all these conditions are the same thing with different labels.
Clinical experiences still differ sharply: someone with schizophrenia will face challenges distinct from a person with anorexia or Tourette syndrome.
The work also doesn’t provide a simple genetic test that can predict a future diagnosis.
Each variant usually nudges risk only slightly.
Dozens or hundreds of such nudges, combined with stress, nutrition, infections, social support and more, shape what actually happens.
For families, the message is mixed but useful.
Seeing several different diagnoses in one family does not mean the family is uniquely “unlucky”; it points toward shared genetic factors that science is beginning to map.
Some key terms worth unpacking
A few concepts from this research crop up often in genetics news, and they can sound more mysterious than they are.
- Gene variant: A small difference in DNA code between individuals, often just one “letter” change. Many variants are harmless; some alter how genes work.
- Gene regulation: The process that decides when, where and how strongly a gene is switched on. Mis-timed activation can disrupt development.
- Protein network: Genes code for proteins, and proteins interact in chains and webs. A change in one protein can affect many others, like knocking over a domino.
- Pleiotropy: One variant influencing several traits or conditions, rather than a one-gene–one-effect relationship.
Thinking in terms of networks rather than single “faulty genes” fits psychiatry particularly well, because mental health involves many brain systems working together.
Where this line of research could lead next
The new findings raise several practical questions for the next decade of mental health research.
One route is to test whether people with different diagnoses but similar genetic risk profiles respond better to the same types of treatment.
Another is to track how these pleiotropic variants interact with real-world experiences such as early stress, nutrition, or sleep disruption.
Researchers could also model these variants in organoids – tiny clumps of human brain tissue grown in the lab – to watch how cell networks develop across time.
Outside the lab, this kind of work feeds into debates over how psychiatric conditions are defined.
If diagnoses share a common genetic backbone, clinicians may eventually shift toward describing underlying dimensions such as cognitive flexibility, social communication or emotional regulation, rather than rigid categories.
For patients and carers, the immediate takeaway is not a new pill or test, but a clearer view of why mental health diagnoses often blend into one another, and why families can see a patchwork of labels across generations instead of a single recurring condition.
