Massive study reveals genetic risk for mental illness often points to multiple disorders

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A sweeping new study of over two million people in Sweden has found that the genetic risk for mental illness often points toward multiple disorders, not just the one diagnosed. The study, led by Dr. Kenneth S. Kendler of Virginia Commonwealth University, calculated a measure called "genetic specificity" for nine major psychiatric and substance use disorders. The results showed a wide range, with schizophrenia having the highest genetic specificity at 73.1% and drug use disorder the lowest at 29.5%. The findings suggest that some diagnostic categories may be less distinct at the genetic level than previously assumed, and that genetic specificity can be modified by clinical features like age of onset, recurrence, and treatment setting.

Why it matters

This study challenges long-held assumptions about the genetic distinctness of psychiatric disorders, with implications for how researchers design genetic studies and how clinicians think about diagnostic boundaries. The discovery that genetic specificity can shift based on clinical factors like age of onset and treatment setting also suggests new ways that this information could be used to refine prognosis and guide treatment decisions.

The details

The research team analyzed data from over two million individuals born in Sweden between 1950 and 1995, drawing from national patient registries and primary care records. They calculated genetic specificity - the percentage of total inherited risk in a person with a given diagnosis that points toward that specific diagnosis rather than others. Schizophrenia had the highest specificity at 73.1%, followed by bipolar disorder at 54.8% and alcohol use disorder at 54.1%. In the middle tier were ADHD (48.2%), autism (47.5%), and PTSD (47.4%). The conditions with the most blurred genetic identities were major depression (41.1%), anxiety disorder (38.6%), and drug use disorder (29.5%). Genetic specificity also varied based on clinical features, with earlier onset and more recurrent episodes associated with higher specificity. Interestingly, bipolar patients treated in hospitals had much higher specificity than those seen only in primary care.

• The study analyzed data on individuals born in Sweden between 1950 and 1995.
• The research article was published on March 3, 2026.

What they’re saying

What’s next

Researchers plan to explore whether the genetic specificity hierarchies found in this Swedish population hold true in other ethnic and geographic cohorts. They also suggest that clinicians and researchers could begin using specificity-related markers, age at onset, recurrence patterns, and treatment history to refine prognosis and guide treatment decisions.