Large-scale studies show shared risk pathways across diagnoses — helping explain comorbidity and pointing to more personalized care.

Establishing a diagnosis for a psychiatric disorder is not a simple process. Although many people may feel that it means you thumb through the latest edition of the DSM (Diagnostic and Statistical Manual of Mental Disorders) published by the American Psychiatric Association, and there you have it. It’s not that simple.

I found that out when I began as an intake person at a mental health center and had to decide on diagnoses for people who were coming to the center. Nothing was ever clearly one diagnosis without others. Also, many people had two or three diagnoses, and perhaps even a medical condition that could have contributed to those diagnoses.

To say that I was opening my eyes to the realities of our inability for specificity in psychiatric diagnosis is not an understatement. We were in uncharted territory and had been led to believe that things would be fine if only we read the DSM carefully. Now we know that’s not so.

Most people don’t encounter mental illness in tidy categories. They encounter it in lived combinations: a teenager whose panic attacks come with a heavy sadness; a new parent who can’t sleep because worry and intrusive thoughts keep cycling; an adult who recovers from substance use only to discover that untreated trauma has been steering the wheel the whole time. Clinicians have long had a word for this “stacking” of symptoms — comorbidity — but until recently, we had only partial explanations for why it happens so often.

One reason overlaps matter is practical: they can change how a person is treated and how they understand themselves. If depression and anxiety show up together, is that two separate problems — or one shared vulnerability expressing itself in two ways? And if someone meets criteria for both bipolar disorder and psychosis-spectrum symptoms at different points in life, are we sure the boundary between those diagnoses is as firm as our manuals imply? New genetic research is pushing psychiatry to take those questions seriously, not as philosophy, but as data.

What About Genetics and Vulnerability?

In December 2025, an unusually large and rigorous study in Nature analyzed genetic data from 14 major psychiatric disorders, drawing on samples that together included more than a million cases. The core finding was simple yet disruptive: many psychiatric diagnoses share substantial genetic risk, meaning the same DNA variations can increase vulnerability to more than one condition.

That doesn’t mean genes “cause” a disorder in a direct, single-switch way. Instead, it suggests that multiple diagnoses can arise from overlapping biological tendencies — especially those that shape how the brain processes threat, reward, learning, and emotional regulation.

Using statistical modeling, the researchers found that the 14 disorders tended to cluster into five broader genetic groupings — essentially families that share common roots. A university summary of the same work, aimed at a general audience, described these groupings in ways that mirror what many clinicians observe in practice: disorders that revolve around compulsivity (such as OCD and related patterns), internalizing problems (like depression, anxiety, and PTSD), neurodevelopmental conditions (including ADHD and autism-spectrum diagnoses), mood–psychotic spectrum disorders (including schizophrenia and bipolar disorder), and substance use disorders. In everyday language, the data suggest that many of our current labels may reflect different “faces” of shared vulnerabilities rather than completely separate diseases.

News coverage highlighted how striking the pattern is: the analysis didn’t merely find a small overlap — it found coherent clusters, each tied to sets of genetic variants that recur across multiple diagnoses. This helps explain a common clinical reality: a person may start with anxiety, then develop depression; another might show early attention problems, later develop mood instability; another might cycle through compulsive behaviors and substance use. The overlap is not just a quirk of diagnosis — it may be a feature of underlying biology. Once again, we’re faced with the nature vs. nurture debate, but here it’s even more complicated.

Two genetic concepts help clarify this. A single gene variant can influence multiple traits. In psychiatry, some genetic influences don’t respect diagnostic boundaries. A detailed review of cross-disorder genetics shows that this shared influence appears at multiple levels — from genome-wide correlations to specific biological pathways and individual loci. For example, if a biological pathway affects how the brain learns from stress, that same pathway might increase the risk of anxiety in one person and depression in another — or both in the same person — depending on life experiences and other biological factors.

Consider now that most psychiatric disorders are influenced by many genetic variants, each with a small effect. When conditions are highly polygenic, it becomes more likely that different diagnoses will share some risk variants simply because there are so many contributors. A 2025 review summarizes this pattern as pervasive overlap paired with high polygenicity — lots of shared signal, plus many tiny effects spread across the genome. In other words, psychiatry is not dealing with single-gene illnesses; it is dealing with complex risk “weather systems,” where different storms can form from overlapping conditions. Complex? You bet it is and its significance lies in treatment for these individuals.

Fluctuating Diagnoses

These patterns also align with a general vulnerability factor for psychopathology, often described as a “p factor.” You can think of it as a shared baseline susceptibility — like a lower threshold for stress-related disruption — that can manifest differently depending on developmental stage, learning history, social environment, and protective factors. Many factors, many diagnoses, and many symptoms.

It’s tempting to hear “genetic overlap” and worry that it reduces a person to biology. It shouldn’t. As the saying goes, genes load the gun, but the environment often pulls the trigger — except even that metaphor is too simple. Biology and experience braid together.

Trauma, chronic stress, sleep disruption, substance exposure, social isolation, discrimination, and economic insecurity can all shape how genetic vulnerability is expressed. Overlap, then, is not destiny; it explains why symptoms can cluster and shift over time.

Clinically, the overlap offers a hopeful message: if multiple diagnoses share pathways, treatments could be designed to target shared mechanisms rather than one disorder at a time. That could mean fewer medication “trial and error” cycles and greater precision. Currently, as many people know, medication for psychiatric disorders is a hit-or-miss process. Too many patients have to be put on short-term trials of too many medications and then they want to give up and not take anything. We can all understand their frustration.

Some researchers are already examining shared genetic architecture across psychiatric conditions and other health risks because patients often have both mental and physical health struggles. If we can identify common biological routes, we may be able to predict who needs early screening for sleep problems, inflammation-related issues, or substance-related risk alongside mood symptoms. If you will recall, inflammation is seen as one of the underlying factors in specific psychiatric disorders such as depression and most probably anxiety.

Future Diagnostic Change

Over time, research may reshape how diagnosis is framed. Today’s diagnostic manuals are largely symptom-based because symptoms are what clinicians can reliably observe. But symptom-based categories can miss what’s happening beneath the surface.

A major advantage of cross-disorder genetics is that it points toward biology-informed groupings — not to erase diagnoses overnight, but to complement them. The review on genetic and phenotypic similarity argues that overlaps appear across many levels of observation, not just at the DNA level — supporting the idea that our current boundaries may be more porous than we assume.

And understanding overlap can reduce shame. People blame themselves when one diagnosis becomes two, or two become three, as if it reflects personal failure. It’s not. In reality, it often reflects how vulnerability works. If you’ve ever felt like you’re playing diagnostic “whack-a-mole,” this research offers reassurance: it’s not that you’re broken in new ways every year. It may be that the same underlying system is asking for help in different languages.

The emerging picture also invites compassion. When a loved one seems to “change diagnoses,” it can appear uncertain or inconsistent. Genetic overlap suggests that shifting presentations may be expected in some people, especially during developmental transitions such as adolescence, the postpartum period, or later-life medical changes. Better science provides more realistic expectations and earlier, kinder intervention.

None of this means the differences between disorders are imaginary. People with schizophrenia can experience realities profoundly different from those with panic disorder; people with anorexia face risks that require specialized care; substance use disorders carry unique medical dangers. The point is not sameness. The point is connectedness: shared roots with different branches. Recognizing what patients have always needed — treatment that respects their specific symptoms while addressing the broader vulnerabilities that may connect them.

As research expands, the next step is to translate shared genetic signals into actionable understanding: which brain cells and circuits are affected, how development alters risk, and which interventions — therapy, medication, sleep stabilization, social support, prevention programs — most effectively address the pathway. Overlap isn’t merely diagnostic noise. It is part of the underlying architecture of mental illness. You could compare it to a forest that has many different types of trees. Yes, it’s a forest, but there are many different trees in it.