A large international genetics study suggests that 14 common psychiatric disorders share significant genetic similarities, raising questions about treating those conditions as entirely separate illnesses.
Researchers analyzed psychiatric and genetic data from more than six million people, including over one million individuals diagnosed with at least one mental health disorder and roughly five million people without a diagnosis. The results were published in the journal Nature.
The study found that these disorders cluster into five broad genetic groups rather than existing as isolated illnesses.
Those categories include substance use disorders, internalizing conditions such as depression and anxiety, neurodevelopmental disorders such as autism and attention-deficit hyperactivity disorder, compulsive disorders including obsessive-compulsive disorder and anorexia nervosa, and a group consisting of bipolar disorder and schizophrenia.
More than half of patients diagnosed with a psychiatric disorder eventually receive two or more additional diagnoses, a pattern the researchers say their findings help explain.
Andrew Grotzinger, an assistant professor of psychology and neuroscience at the University of Colorado Boulder and a co-author of the study, said the current diagnostic system can unintentionally discourage patients. He compared the practice to diagnosing a patient with separate illnesses for a runny nose, cough, and sore throat, rather than recognizing a single underlying cause.
The genetic analysis revealed that the 14 disorders share hundreds of genetic variants linked to brain function. Researchers identified at least 238 shared genetic variants in one analysis, and more than 400 variants in another, depending on the methods used. Many of these variants appear to influence the development and communication of specific brain cells.
Some overlaps were especially striking. Bipolar disorder and schizophrenia were found to share roughly two-thirds to 70 percent of their genetic risk factors. Major depression, anxiety disorders, and post-traumatic stress disorder shared as much as 90 percent of their genetic risk in certain analyses.
Jordan Smoller, director of Mass General Brigham’s Center for Precision Psychiatry and a senior author on the study, said the genetic patterns suggest that current diagnostic boundaries may not fully reflect biological reality. He noted that the findings help explain why some medications, such as antidepressants, can be effective across multiple conditions.
Researchers also identified specific genetic hot spots linked to multiple disorders.
One notable region on chromosome 11 was associated with increased risk for eight psychiatric conditions. That region includes the DRD2 gene, a primary target of antipsychotic drugs that regulate dopamine, a chemical messenger involved in motivation, mood, and cognition.
The study was conducted by the Psychiatric Genomics Consortium’s Cross-Disorder Working Group, which includes scientists from institutions across the United States and Europe. The analysis took five years to complete and represents one of the largest efforts to map the genetic structure of mental illness.
Kenneth Kendler, a professor of psychiatry at Virginia Commonwealth University and a co-chair of the research group, said psychiatry lacks the kind of laboratory tests common in other medical fields. He said genetics offers a promising tool for understanding why mental disorders so often overlap, even if clinical applications remain limited for now.
Some researchers have also cautioned against interpreting the results as proof that all patients with the same diagnosis share identical biology. Personalized care remains essential, especially given that treatments often work for only a subset of patients.
Authors of the study acknowledged limitations, including the fact that most genetic data analyzed came from people of European ancestry. Ongoing research aims to expand genetic databases to include more diverse populations.
Despite those limitations, many experts view the findings as a significant step toward a more biologically grounded understanding of mental illness. While genetics alone will not replace clinical judgment, researchers say the study provides a stronger scientific framework for rethinking how psychiatric disorders are classified and eventually treated.