Why does it? depression often with anxiety? Why are the symptoms of trauma, drug use, and mental health problems so often intertwined? For many patients, more than one mental diagnosis can be confusing and frustrating, leaving them wondering if the initial diagnosis was wrong or worse. But a major new study suggests another possibility: Many mental disorders are linked because some of their biological roots are also linked.
In a study conducted in NatureThe Psychiatric Genomics Consortium Working Group analyzed the genetic data of more than 1 million people. childhood– or adult mental illness and nearly 5 million undiagnosed. The researchers examined 14 conditions and found that the diagnoses fit into broader and partially overlapping families:
- Internal disturbances: major depression, anxiety disorders and aftervulnerable stress disorders (PTSD).
- Schizophrenia and bipolar disorder.
- Obsessive compulsive disorder: obsessive-compulsive disorder (OCD), anorexia nervosa and, to a lesser extent, Tourette’s syndrome.
- Substance use disorder: alcohol use disorders, nicotine dependence, opioid use disorders, and cannabis use disorders.
- Neurodevelopmental disorders: autism spectrum disorder, attention– attention deficit/hyperactivity disorder (ADHD) and to a lesser extent, Tourette syndrome.
Some of the encounters were interesting. Major depression, anxiety disorders, and PTSD share about 90 percent of their genetic risk, while schizophrenia and bipolar disorder share about 66 percent of their genetic traits.
The findings support what many clinicians are already seeing in practice. Depression and anxiety often involve processes such as rumination, avoidance, sleep disturbance, threat sensitivity, and emotional regulation difficulties. PTSD can include depression, anxiety, irritability, and drug use as an attempt to manage the overwhelming excitement. ADHD can co-exist with anxiety or substance abuse, not because the person is inattentive or weak, but because attention, impulse control, reward sensitivity, and stress regulation are all intertwined.
Geneticshowever, there is no fate. A genetic association does not mean that a person is destined to develop the disorder. Environment, trauma, relationships, discriminationpoverty, culture, sleep, physical health and access to care all make up mental health. The study tells us something important about population-level risk; it does not reduce a person to their DNA.
The study also points to future treatment possibilities. Genetically clustered disorders showed similarities in when certain genes were active during development and which types of brain cells were affected. For example, attachment disorder was most strongly associated with genes expressed in oligodendrocytes, while schizophrenia and bipolar disorder were most strongly associated with genes expressed in excitatory neurons. These findings are early, but they could guide future efforts to develop or repurpose treatments for conditions that commonly co-occur.
For patients, referrals are more human than technical: having multiple diagnoses isn’t a personal failing, and it doesn’t mean your symptoms are “all over the place.” Comorbidity common because the mind and brain do not organize themselves according to the chapters in the diagnostic manual.
For clinicians, research reinforces the value of treatment across categories. A patient with depression and anxiety may benefit from approaches that target shared processes rather than treating each diagnosis as an isolated entity.
But the research offers a useful shift in perspective. Mental disorders can be listed separately, but they often travel together because they share vulnerability. Understanding these common roots can help reduce it stigmaimprove care and remind us that people are more complex than any labels.
