New genetic evidence hints they may be more tightly linked.
A major study published in early 2025 suggests that many well-known mental health disorders share a surprisingly deep genetic foundation, reshaping how scientists think about diagnosis, risk, and treatment.
A shared genetic thread behind eight disorders
Researchers in the US have shown that eight different psychiatric conditions appear to arise, at least partly, from the same set of genes.
The disorders linked in the work are:
- Autism
- Attention deficit hyperactivity disorder (ADHD)
- Schizophrenia
- Bipolar disorder
- Major depressive disorder
- Tourette syndrome
- Obsessive-compulsive disorder (OCD)
- Anorexia nervosa
These conditions can look very different in the clinic. One affects mood, another eating, another thinking and perception. Yet the new findings show that they overlap at the level of DNA in a way that is hard to ignore.
Dozens of the same genetic switches appear to nudge brain development towards a range of psychiatric outcomes, depending on when and where they act.
The study builds on work from 2019, when an international team first identified 109 genes that were linked, in different combinations, to those eight disorders. The new research goes a step further, drilling into how specific variants in those genes behave during brain development.
What the new study actually did
The team examined nearly 18,000 genetic variants across both shared and disorder-specific genes. They inserted these variants into precursor brain cells – the immature cells that later become neurons – to see how they alter gene activity.
By watching what happened in these human-derived cells, and then checking similar processes in developing mouse neurons, the scientists could track which variants disrupt normal gene regulation.
They identified 683 variants that changed how genes are switched on and off in brain cells. Many of those were linked to more than one disorder.
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Variants that increase risk for several different conditions tend to sit at key control points in the brain’s genetic wiring.
These multi-use variants are known as “pleiotropic” – a term used when one genetic change influences multiple traits or conditions.
Pleiotropy: one variant, many outcomes
Pleiotropy is not new in genetics, but this study shows how influential it may be in psychiatry.
The team found that pleiotropic variants:
- Interact with many more proteins than disorder-specific variants.
- Affect a broader range of brain cell types.
- Remain active across several stages of brain development.
- Tend to sit in regulatory regions that control cascades of other genes.
That means a single variant can subtly distort multiple biological processes, from how neurons grow, to how they connect, to how they communicate with each other.
In effect, these shared variants behave like central junctions in a busy rail network: a fault there will not just delay one train, but disrupt entire routes.
The same underlying genetic nudge might push one person towards ADHD, another towards depression, and a third towards both.
This shared legacy helps explain why these conditions tend to cluster in families, and why individuals often receive more than one diagnosis. For example, studies suggest that up to 70 percent of people with autism also meet criteria for ADHD, and vice versa.
Why this blurs traditional diagnoses
Psychiatric categories were largely defined before genetics came into play, based on symptoms that patients reported and clinicians observed.
The new findings highlight how messy those boundaries may be biologically. Two people can look very different in the clinic, yet share many of the same genetic risk factors acting in the brain.
| Aspect | Traditional view | Genetic view from new study |
|---|---|---|
| Disorders | Distinct and separate conditions | Overlapping syndromes with shared roots |
| Genetic risk | Each disorder has its own genes | Many key genes influence several disorders |
| Family patterns | Curious but unexplained overlaps | Expected when shared variants run in families |
| Treatment vision | One diagnosis, one specific therapy | Shared therapies targeting common pathways |
One of the study’s authors described pleiotropy as a “challenge” for traditional classification, because it makes clean diagnostic boxes harder to defend. Yet it also opens the door to a different kind of psychiatry, focused on the biology that cuts across labels.
New hope for broad-acting treatments
Because these pleiotropic variants sit in central regulatory hubs, they could make efficient targets for new therapies.
A future medication might be designed not for “depression” or “OCD” alone, but for a shared circuit that drives vulnerability to several conditions.
That does not mean a single pill will flatten all differences between disorders. Each condition still has unique genetic and environmental factors. Yet therapies aimed at shared pathways could ease symptoms in more than one diagnosis at once, or prevent progression from one condition to another.
For drug developers, this approach might be more realistic than chasing dozens of separate targets for every diagnostic category.
Why timing in brain development matters
One of the study’s striking points is that many shared variants stay active over long stretches of brain development.
Some are switched on early, when neural stem cells are dividing. Others remain engaged later, when neurons are forming connections and refining networks. A single variant can influence different steps along this timeline.
That flexibility in timing may help explain why people with similar genetic risk can end up with different diagnoses. Subtle differences in when those variants have their strongest effect, combined with environment and life events, could steer development in multiple directions.
What this might mean for families
For relatives of people with psychiatric conditions, the shared genetic basis cuts both ways.
- It can help explain why several members of a family receive different diagnoses across the same cluster of conditions.
- It suggests that mental health history in a family may point to a broader vulnerability, not just to one specific disorder.
- It underscores that these conditions are not a matter of “willpower” or “character”, but are deeply tied to brain biology.
At the same time, genes are not destiny. Many people carry risk variants and never develop a diagnosed condition. Lifestyle factors, social support, trauma, education, and access to care all play powerful roles alongside biology.
Putting some key terms in plain language
The study leans on concepts that can sound abstract, so a few definitions help:
- Genetic variant: A small difference in DNA sequence between people, such as a single “letter” change in the genetic code.
- Gene regulation: The process by which cells decide which genes to switch on or off, and by how much.
- Protein-protein interaction: Proteins in cells often work in teams. An interaction means two or more proteins physically connect or influence each other’s actions.
- Precursor neuron: An immature brain cell that has not yet fully specialised into a specific type of neuron.
When a variant affects gene regulation rather than the core structure of a protein, its impact can be very context-dependent. It might be harmless in one cell type or life stage, yet disruptive in another. That fits well with the varied ways psychiatric conditions show up across age and environment.
Real-life scenarios and future risks
Imagine two siblings who both inherit a set of pleiotropic risk variants. One grows up in a stable home, with early support for attention and learning problems. The other faces bullying, chronic stress, and little access to care. Their brains carry similar vulnerabilities, but the outcomes could be very different: one develops mild ADHD symptoms, the other lives with severe depression and OCD.
This kind of scenario reflects what geneticists already see in population studies. Shared genetic roots set the stage, but life experiences shape how that script is read.
The World Health Organization estimates that around one in eight people globally live with a psychiatric condition. As genetic studies grow larger and more detailed, the number of shared variants is likely to rise. That brings opportunities and risks:
- Better prediction tools might identify people at high risk earlier, allowing targeted support.
- Poorly regulated use of genetic data could fuel stigma or discrimination if handled without care.
- Drug development may shift towards treatments aimed at shared biological pathways rather than narrow diagnostic labels.
For patients and families, the headline message from this study is subtle but powerful: many psychiatric diagnoses may be different branches growing from some of the same roots. Understanding those roots could eventually change how mental health is talked about, treated, and funded.
Originally posted 2026-03-04 00:38:40.