Genetically, they are more similar than they are unique
For more than a century, psychiatry has named and sorted the mind's suffering into distinct categories — schizophrenia, bipolar disorder, depression — as though each were a separate country with its own borders. A sweeping genetic study of over a million people now suggests those borders may be largely cartographic fiction: beneath fourteen recognized psychiatric disorders lie just five shared biological signatures, with schizophrenia and bipolar disorder overlapping so profoundly that their separation as distinct diseases is now in question. The finding does not diminish the reality of individual suffering, but it invites medicine to ask whether it has been treating the map rather than the territory.
- A study of more than one million patients has collapsed fourteen psychiatric diagnoses into just five underlying genetic clusters, fundamentally destabilizing how the field understands mental illness.
- Schizophrenia and bipolar disorder — long treated as separate diseases — share 70% of their genetic architecture, raising urgent questions about whether millions of patients have been misclassified and mistreated for decades.
- Pleiotropic genes, which influence multiple conditions simultaneously, are proving to be the hidden architects of psychiatric risk, active across more brain cell types and developmental stages than previously understood.
- Researchers now believe a single therapy targeting shared genetic factors could replace the current patchwork of disorder-specific drugs and interventions that burden the nearly one billion people living with psychiatric conditions worldwide.
- The field faces a race against time: translating these genetic insights into revised diagnostics and new treatments before another generation of patients is filtered through a classification system that biology may no longer support.
For decades, psychiatry has organized mental illness into distinct categories — schizophrenia here, bipolar disorder there, depression in its own corner. The system appeared logical: different symptoms, different diagnoses, different treatments. A landmark genetic study is now challenging whether that entire framework reflects biological reality.
Researchers analyzed DNA from more than a million people diagnosed with one of fourteen psychiatric disorders, comparing them against five million people with no psychiatric diagnosis. Rather than finding fourteen separate genetic blueprints, they discovered just five underlying genetic signatures accounting for the bulk of psychiatric risk across all conditions. Compulsive disorders clustered together; depression, anxiety, and PTSD formed another group; substance use disorders a third; neurodevelopmental conditions like autism and ADHD a fourth. The fifth finding was the most striking: schizophrenia and bipolar disorder shared so much genetic material — 70% of the signal — that their status as separate diseases became genuinely questionable.
The mechanism involves pleiotropy: genes that influence multiple traits at once. Earlier research had identified 109 genes associated in varying combinations with eight psychiatric disorders. When scientists introduced thousands of genetic variants into developing neuron precursor cells, they found that pleiotropic variants — those affecting multiple conditions — were involved in far more protein interactions, active across more brain cell types, and engaged across more stages of brain development than variants unique to single disorders. Their ability to shape cascading biological networks explained why the same genetic variants could produce such different psychiatric presentations.
Andrew Grotzinger of CU Boulder, one of the study's lead researchers, noted that genetically, these disorders are more alike than different. The current symptom-based diagnostic system often results in patients carrying multiple diagnoses and multiple medications. But if the underlying biology is shared, a single intervention targeting common genetic factors could potentially address what medicine now treats as several separate illnesses.
With roughly one billion people worldwide living with some form of psychiatric condition, the stakes of reclassification are immense. A diagnostic system refined over more than a century may be approaching fundamental revision — and the central question now is whether psychiatry can move quickly enough to bring its clinical practice in line with what the genome is revealing.
For decades, psychiatry has sorted the mind's disorders into neat categories: schizophrenia here, bipolar disorder there, depression in its own corner. The system made sense on the surface—different symptoms, different diagnoses, different treatments. But a series of landmark genetic studies is now suggesting that this entire framework may be built on a misunderstanding of what these conditions actually are.
Last year, researchers examined DNA from more than a million people diagnosed with at least one of fourteen psychiatric disorders, comparing their genetic profiles against five million people with no psychiatric diagnosis. What they found was unexpected: instead of fourteen separate genetic blueprints, the data revealed just five underlying genetic signatures that account for the bulk of psychiatric risk across all those seemingly distinct conditions. The implication was stark. These disorders, which patients and clinicians have long treated as fundamentally separate illnesses, may actually be variations on a smaller number of shared biological themes.
The five genetic clusters that emerged from the data mapped onto recognizable patterns. Compulsive conditions—anorexia nervosa, Tourette syndrome, obsessive-compulsive disorder—clustered together. Depression, anxiety, and post-traumatic stress disorder formed another group. Substance use disorders made a third. Neurodevelopmental conditions like autism and ADHD constituted a fourth. But the fifth finding was the most jarring: schizophrenia and bipolar disorder shared so much genetic material that seventy percent of the genetic signal associated with schizophrenia also appeared in bipolar disorder. The overlap was so substantial that it raised a fundamental question: should these two conditions even be classified as separate diseases at all?
Andrew Grotzinger, an assistant professor of psychology and neuroscience at CU Boulder and one of the study's lead researchers, framed the implications plainly. Genetically, he observed, these disorders are more alike than different. The current system of diagnosis—based on observable symptoms in a clinical room—often results in patients receiving multiple diagnoses and multiple medications, each targeting a different named condition. But if the underlying biology is shared, the entire treatment strategy might be misaligned. A single intervention targeting the shared genetic factors could potentially address what we now call several separate illnesses.
The mechanism behind this overlap involves what geneticists call pleiotropy: genes that influence multiple traits or, in this case, multiple psychiatric conditions. Earlier research had identified 109 genes associated in different combinations with eight psychiatric disorders. When scientists introduced nearly eighteen thousand variations of these shared and unique genes into precursor cells that would become neurons, they could observe how the genes affected expression during human development. The work identified 683 genetic variants that impacted gene regulation. Crucially, the pleiotropic variants—those affecting multiple conditions—were involved in far more protein-to-protein interactions than variants unique to specific disorders. They were also active across more types of brain cells and engaged in regulatory mechanisms that shaped multiple stages of brain development. This ability to influence cascades and networks of biological processes explained why the same genetic variants could contribute to different psychiatric presentations.
Traditionally, pleiotropy had been viewed as a complication, a messy fact that made psychiatric classification harder. But researchers now see it differently. If the shared genetic basis of these disorders can be understood, treatments could be designed to target those shared factors—potentially treating multiple conditions with a single therapy rather than requiring separate pills and separate psychotherapy interventions for each diagnosis.
The World Health Organization estimates that roughly one in seven people globally—nearly a billion individuals—live with some form of psychiatric condition. If the genetic architecture of these disorders is truly as overlapping as the research suggests, the implications for treatment could be enormous. The current diagnostic system, refined over more than a century, may be on the verge of fundamental revision. The question now is whether psychiatry can move fast enough to translate these genetic insights into clinical practice before another generation of patients cycles through the old framework of separate diseases and separate treatments.
Notable Quotes
Genetically, we saw that they are more similar than they are unique. By identifying what is shared across these disorders, we can hopefully come up with strategies to target them in a different way that doesn't require four separate pills or four separate psychotherapy interventions.— Andrew Grotzinger, assistant professor of psychology and neuroscience at CU Boulder
This work provides the best evidence yet that there may be things that we are currently giving different names to that are actually driven by the same biological processes.— Andrew Grotzinger
The Hearth Conversation Another angle on the story
So if schizophrenia and bipolar disorder share seventy percent of their genetic basis, what does that actually mean for someone living with one of these diagnoses right now?
It means the label they carry might be capturing something real about their symptoms, but missing something equally real about the underlying biology they share with people labeled differently. Right now, a person might get one diagnosis and one medication regimen, while someone else with overlapping genetic risk gets a completely different treatment plan. The genetics suggest those plans might be addressing the same root problem in different ways.
But symptoms are different, aren't they? Schizophrenia and bipolar disorder look nothing alike in the clinic.
They look different on the surface, yes. But the research suggests that's partly because we're looking at the downstream effects of shared genetic machinery expressing itself in different ways. The genes involved in pleiotropy—the ones that affect multiple traits—are active across many types of brain cells and influence development at multiple stages. The same genetic variant could tip toward one presentation in one person and another presentation in someone else, depending on other genetic and environmental factors.
Does this mean the researchers are saying we should stop using the words schizophrenia and bipolar disorder?
Not necessarily. The symptoms are real and matter clinically. But it suggests that our current way of organizing these conditions—as fourteen separate diseases—might be like organizing animals by whether they fly or swim, when what actually matters is their underlying physiology. You might need different approaches for different presentations, but you'd be targeting shared biological mechanisms rather than treating them as fundamentally distinct illnesses.
What would change in practice if psychiatry actually adopted this framework?
Instead of a patient receiving four separate medications for four separate diagnoses, they might receive one or two treatments designed to address the shared genetic factors driving their symptoms. It would require rethinking how we train psychiatrists, how we design clinical trials, and how we think about what a diagnosis actually means. But for someone struggling with multiple psychiatric conditions, it could mean fewer pills, fewer side effects, and treatments actually designed around their biology rather than around historical categories.
How confident are researchers that this genetic overlap is real?
Confident enough that major journals like Nature and Cell published the work. The study examined over a million people—the largest of its kind. The five genetic clusters emerged consistently across the data. The pleiotropy findings were replicated in cellular and animal models. It's not perfect, and there's more work to do, but this isn't speculative. The genetic overlap is there.