During the study, the DNA of more than six million people was analyzed, among whom over a million had at least one mental disorder. According to the World Health Organization, more than a billion people suffer from such disorders.
“Currently, psychiatric diagnoses are made based on observations during consultations, and many patients are given multiple diagnoses at once. This complicates treatment and causes frustration for patients,” noted Andrew Grotzinger, an assistant professor of psychology and neuroscience at the University of Colorado and the lead author of the study.
The researchers examined 14 different psychiatric disorders and found that a significant portion of the genetic differences between individuals with these disorders and those without could be explained by five main genetic patterns. These patterns were associated with 238 genetic variants that affect brain development and functioning, allowing the disorders to be grouped into five categories.
The first group includes disorders with compulsive manifestations, such as anorexia nervosa, Tourette syndrome, and obsessive-compulsive disorder. The second group encompasses internal disorders, including depression, anxiety disorders, and post-traumatic stress disorder. The third category is related to disorders caused by the use of psychoactive substances, while the fourth includes neurodevelopmental disorders such as autism and attention deficit hyperactivity disorder. The fifth group includes bipolar disorder and schizophrenia, which, according to the study, share about 70% of the common genetic signal.
These two conditions have traditionally been considered quite distinct, and combined diagnoses are rarely assigned to the same patient.
“From a genetic standpoint, we found that these disorders have more in common than unique characteristics,” added Grotzinger.
Implications for Patients
The results of the study, published in the journal Nature, challenge traditional views of mental disorders as separate diseases. Instead, they suggest that many of them may be linked to common biological processes.
Nevertheless, the scientists emphasize that current diagnostic approaches should not be changed at this time. They hope that the collected data will serve as a foundation for future updates to the Diagnostic and Statistical Manual of Mental Disorders (DSM), used by specialists worldwide.
“This study provides the most compelling evidence to date that some disorders we currently label differently are actually related to the same biological processes,” noted Grotzinger.
“We hope that identifying the common features of these disorders will allow us to propose new treatment strategies that will be more effective and not require multiple different medications or psychotherapeutic interventions,” he added.
Additionally, the study highlighted specific biological pathways associated with different groups of disorders. For example, individuals with bipolar disorder and schizophrenia had more active genes affecting excitatory neurons that transmit signals in the brain. In cases of depression and anxiety disorders, genetic variants related to oligodendrocytes—specialized cells that support and protect the brain's conducting pathways—were more frequently observed.
Some common genetic factors are believed to influence brain development even before birth, while others become more significant in adulthood, which may explain the overlaps between mental disorders.
A 2018 review showed that more than half of people with one psychiatric diagnosis later receive at least one more, and about 41% meet the criteria for four or more diagnoses over their lifetime.
