Psychiatrists have long relied on diagnostic manuals that regard most mental-health conditions as distinct from one another — depression, for instance, is listed as a separate disorder from anxiety. But a genetic analysis of more than one million people suggests that a host of psychiatric conditions have common biological roots.

The results, published today in Nature, reveal that people with seemingly disparate conditions often share many of the same disease-linked genetic variants. The analysis found that 14 major psychiatric disorders cluster into five categories, each characterized by a common set of genetic risk factors. The neurodevelopmental category, for example, includes both attention deficit hyperactivity disorder and autism, which psychiatric handbooks classify as separate conditions.

Many supposedly individual conditions are “ultimately more overlapping than they are distinct, which should offer patients hope”, says study co-author Andrew Grotzinger, a psychiatric geneticist at the University of Colorado Boulder. “You can see the despair on someone’s face [when] you give them five different labels as opposed to one label.”

The researchers found that the 14 mental-health conditions they studied generally fall into five distinct buckets, each with its own genetic profile. There’s a schizophrenia/bipolar disorder category; an ‘internalizing’ category that includes depression, anxiety and post-traumatic stress disorder; a neurodevelopmental category; and a compulsive category that includes obsessive-compulsive disorder and anorexia.

A final category includes substance-use disorders such as alcohol-use disorder and nicotine dependence. People whose genetic profile corresponds to a given bucket are at elevated risk of any of the conditions in that bucket. Other genetic and environmental triggers also affect risk.

The published results: Mapping the genetic landscape across 14 psychiatric disorders