A new genetic study suggests the boundaries are blurrier.
Fresh research hints that some of the most commonly diagnosed mental health conditions may be deeply connected at the genetic level, raising questions about how we define, understand, and eventually treat them.
A shared genetic thread tying eight conditions together
A US research team has found that eight major psychiatric conditions appear to share a common genetic foundation. The work, published in the journal Cell in early 2025, focuses on specific gene variants that play a role during brain development.
The conditions involved are:
- Autism
- Attention deficit hyperactivity disorder (ADHD)
- Schizophrenia
- Bipolar disorder
- Major depressive disorder
- Tourette syndrome
- Obsessive-compulsive disorder (OCD)
- Anorexia nervosa
These diagnoses look very different in the clinic. One affects mood, another affects appetite, another movement or attention. Yet at a molecular level they may be drawing from some of the same genetic playbook.
Researchers report that hundreds of gene variants are shared across multiple psychiatric conditions and remain active through several stages of brain development.
The results add genetic weight to something psychiatrists have noticed for years: people often live with more than one diagnosis, and the conditions tend to run in the same families.
From 109 genes to 683 high-impact variants
The new work builds on a large 2019 project that first flagged 109 genes connected, in different patterns, to the eight disorders. The latest study goes much deeper, zooming in on specific variants within those genes.
Scientists looked at nearly 18,000 individual genetic changes, some shared among several conditions and some unique to just one. They inserted these variants into precursor cells that later mature into neurons, then watched how gene activity changed.
By tracking these changes, the team identified 683 variants that genuinely altered gene regulation. They then followed up in neurons from developing mice, strengthening the link between these variants and brain development.
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The key variants do not just sit quietly in the genome; they actively shape how brain cells grow, connect, and communicate over time.
This level of detail shifts the conversation from “which genes are involved?” to “what exactly are these genes doing in the developing brain?”
What scientists mean by ‘pleiotropy’
Many of the variants identified fall into a category known as pleiotropic. In genetics, a pleiotropic variant is one that influences multiple traits or conditions at the same time.
In this study, pleiotropic variants showed three striking features:
- They were involved in far more protein-to-protein interactions than variants linked to just one disorder.
- They were active across more types of brain cells.
- They played roles in several stages of brain development, not just one narrow window.
This broad reach may explain why a single variant can nudge the brain towards different outcomes in different people. One family member might develop bipolar disorder, another OCD, and another depression, yet all share some of the same underlying genetic risks.
Why ‘network’ genes matter so much
The proteins produced by these pleiotropic genes appear highly connected to other proteins, forming dense networks inside brain cells. When one piece of such a network changes, the effects can cascade.
Small genetic shifts in network “hub” proteins may ripple outward, altering whole systems that guide how neurons form, fire, and link together.
This network perspective fits with the idea that psychiatric conditions are less about a single “broken” gene and more about vulnerable systems that are pushed off balance by a mix of genetics, life events, and environment.
Rethinking how we define mental illness
For decades, psychiatrists have used symptom-based checklists to separate conditions into distinct categories. Pleiotropy complicates that picture. If the same genetic changes feed into several conditions, then straight-line boundaries between diagnoses start to look artificial.
At the same time, the study does not claim all these conditions are identical. Each disorder still has its own set of unique genetic variants on top of the shared ones. Those unique elements may help tilt a person’s trajectory in one direction rather than another.
| Type of genetic variant | Role in psychiatric conditions | Potential impact on treatment |
|---|---|---|
| Shared (pleiotropic) | Influences several disorders by affecting broad brain-development networks | Could support therapies that benefit multiple conditions at once |
| Condition-specific | Tilts risk toward a particular diagnosis, such as OCD or anorexia | May guide more tailored, disorder-focused interventions |
This dual picture—shared roots plus individual branches—offers a more nuanced view, closer to what many patients actually experience across their lives.
What this could mean for future treatments
At the moment, people with different psychiatric diagnoses often receive very different medicines, or spend years trying a series of drugs that only partly help. The new findings raise the possibility of therapies that target the overlapping biology instead of only the outward symptoms.
Understanding shared genetic pathways opens the door to treatments that might ease several conditions with a single strategy.
For example, if a particular network of proteins is involved in both depression and schizophrenia, a drug or gene-based therapy that stabilises this network could, in theory, reduce symptoms in both groups of patients. That remains a long way off, but the roadmap is now clearer.
There is also a potential benefit for early intervention. If shared genetic risk factors can be identified long before symptoms appear, families might receive closer monitoring, faster referrals, and more targeted support in childhood and adolescence, when the brain is still highly adaptable.
A vast global burden, and a partial explanation
The World Health Organization estimates that around one in eight people worldwide live with a psychiatric condition. That is close to a billion individuals dealing with distress, stigma, and often limited access to care.
Shared genetic risk does not explain everything, and it certainly does not mean mental illness is predetermined. Still, it gives a clearer framework for why some families see multiple diagnoses across generations and why conditions such as autism and ADHD frequently appear together. Studies suggest that up to 70 percent of people with autism also meet criteria for ADHD, or vice versa.
Genes are only part of the story. Environment, trauma, infection, nutrition, and social factors all interact with biology. Yet having a better handle on the genetic architecture offers a way to design more rational, targeted research into those environmental influences as well.
Key concepts behind the research
Several technical ideas sit in the background of this study, but they can be broken down into more familiar terms.
- Gene regulation: not just which genes you have, but when and where they switch on or off. This timing shapes how the brain forms.
- Precursor neurons: immature cells that will eventually become working neurons. Changes at this stage can influence brain wiring for life.
- Protein interaction networks: proteins act less like isolated tools and more like a production line. A fault in one station can disrupt the entire process.
When a variant alters gene regulation in precursor neurons, it can subtly change how those cells grow, migrate, or connect. Multiply that across thousands of cells at key stages of development, and the knock-on effects can set the stage for later mental health problems.
What this might look like in real life
Picture two siblings who both inherit a cluster of pleiotropic variants. One grows up in a relatively calm, supportive environment and develops mild anxiety and occasional depressive episodes. The other experiences bullying, instability, and sleep problems during adolescence and later receives a diagnosis of bipolar disorder.
They share some baseline genetic vulnerability, but different life experiences and additional genetic differences tilt their outcomes. A shared-variant approach suggests that parts of the same treatment toolkit—say, targeting certain neural networks or inflammatory pathways—could still benefit both siblings, even though their labels differ.
Clinicians are already moving towards more personalised psychiatry, using symptom clusters, history, and sometimes brain scans to shape treatment choices. As shared genetic factors become better mapped, genetic profiles may eventually play a supporting role in designing care plans, while still respecting that no gene test can “define” a person or their future.
For now, the main takeaway is subtle but powerful: psychiatric diagnoses that seem miles apart may be closer cousins than they appear, connected through a mesh of shared genes that influence how the brain is built from the very beginning of life.
