A large-scale genetic study of over a million people has identified five underlying genetic groups for 14 psychiatric conditions, suggesting many share common biological causes. This finding offers reassurance to those diagnosed with multiple disorders, indicating a single root cause rather than separate issues. The research highlights significant overlaps, such as between schizophrenia and bipolar disorder.
Researchers analyzed gene variants associated with 14 neurodivergencies and mental health conditions in more than a million individuals, marking the largest study of its kind. The results, published in Nature, reveal that these conditions cluster into five genetic groups rather than being entirely distinct.
Andrew Grotzinger at the University of Colorado Boulder, part of the research team, notes that this is encouraging for patients. "For the millions of people out there who are being diagnosed with multiple psychiatric conditions, this indicates that they don’t have multiple distinct things going on," he says. "I think it makes a big difference for a patient to hear that."
The study found high overlap between schizophrenia and bipolar disorder, with variants in genes active in excitatory neurons, which promote neuron firing. Similarly, major depression, post-traumatic stress disorder (PTSD), and anxiety share variants in genes linked to oligodendrocytes, cells that form myelin sheaths around nerves. Other groupings include attention deficit hyperactivity disorder (ADHD) and autism; obsessive-compulsive disorder (OCD), anorexia nervosa, and Tourette’s syndrome; and substance use disorders with nicotine dependence.
This genetic overlap may explain why two-thirds of people with one psychiatric diagnosis receive additional ones over their lifetime. Grotzinger compares it to diagnosing symptoms of a cold separately: "If you went to the doctor and you had a runny nose, a cough and a sore throat, you wouldn’t want to be diagnosed with runny nose disorder, coughing disorder and sore throat disorder. You’d want to be diagnosed with a cold."
"We’re giving separate labels to things that biologically are not very separable," he adds, though some clinicians argue treatments differ despite minor genetic distinctions.
Avshalom Caspi at Duke University praises the work: "This is an impressive paper. Many mental disorders are not separate disorders, but share common pathways that affect neurodevelopment, cognition and emotion. This is increasingly appreciated now."
Terrie Moffitt, also at Duke, urges shifting away from isolated studies: "Funders should be much more careful about giving grants to researchers who study one disorder at a time, lest a good deal of research resources be wasted."
Limitations include reliance on data from mostly European ancestry individuals and outdated collection methods. Grotzinger cautions against immediate applications like embryo screening, as the functions of these variants remain unclear.
