Psychiatric Conditions Are Genetically Intertwined More Than Once Thought

A major international genetics study is reshaping how scientists understand mental illness, revealing that many psychiatric disorders share far more DNA than previously recognized. The research, published on December 10 in *Nature*, presents the most detailed genetic map to date of overlapping risk across common mental health conditions.

Led by the Cross-Disorder Working Group of the Psychiatric Genomics Consortium, the study was co-chaired by Kenneth Kendler of Virginia Commonwealth University and Jordan Smoller of Harvard Medical School. Together with collaborators worldwide, the team sought to explain why people diagnosed with one psychiatric disorder so often go on to develop others.

Psychiatric conditions rarely occur in isolation. Most patients receive multiple diagnoses over their lifetime, complicating treatment and blurring diagnostic boundaries. While life experiences and environmental stressors play a role, inherited genetic factors are also critical. Until now, however, the extent to which different disorders share genetic roots was not fully understood, according to SciTechDaily.

To address this gap, researchers analyzed genetic data from more than six million people, including over one million individuals diagnosed with psychiatric disorders and five million without diagnoses. By comparing genetic variants across groups, the team identified hundreds of shared risk markers. In total, 428 genetic variants and 101 chromosomal regions were linked to more than one psychiatric condition, highlighting extensive biological overlap.

Using advanced statistical modeling, the researchers grouped 14 psychiatric disorders into five genetically related “families.” These included compulsive disorders such as obsessive-compulsive disorder and anorexia nervosa; internalizing disorders like major depression, anxiety, and post-traumatic stress disorder; neurodevelopmental conditions including autism spectrum disorder and ADHD; a closely linked pair of schizophrenia and bipolar disorder; and substance use disorders involving alcohol, opioids, cannabis, and nicotine.

Some overlaps were striking. Depression, anxiety, and PTSD were found to share nearly 90% of their genetic risk, while schizophrenia and bipolar disorder shared about two-thirds of their genetic markers. These shared genes were also linked to common brain biology. For instance, genes active in oligodendrocytes were more prominent in internalizing disorders, while genes affecting excitatory neurons were more strongly tied to schizophrenia and bipolar disorder.

The findings provide a stronger biological foundation for understanding psychiatric diagnoses and could eventually guide the development of treatments that target multiple related conditions. By clarifying how disorders are genetically connected, the study marks an important step toward more precise and effective mental health care.