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A common set of genes is involved in numerous mental health conditions, according to a study of almost 900,000 genomes. The findings hint that conditions such as anxiety, depression and schizophrenia may all share a physiological basis, and open the door to better diagnosis and treatments.

Verneri Anttila of Harvard Medical School and his colleagues analysed the genomes of around 865,000 people, including those with one of 25 conditions and healthy controls, to see if there were any patterns. Finding these patterns is an important step toward understanding how and why these conditions develop.

The 25 conditions included neurological illnesses such as Alzheimer’s disease and multiple sclerosis, and psychiatric conditions such as depression and post-traumatic stress disorder.

The researchers pooled data from hundreds of different genetic studies, which search for genetic variants that are shared among particular groups of people – those with depression, for example. They could then compare each group with the others to find genetic variants that are shared across different conditions.

They found a strong genetic overlap for mental health conditions, in particular anorexia, obsessive-compulsive disorder (OCD) and schizophrenia. There was much less of an overlap for neurological conditions, suggesting each has a separate cause.

Family ties

We already know that psychiatric conditions run in the family, but the study suggests that the same genetic predisposition could manifest itself in different ways, leading to different conditions. “The same groups of genes predispose us to multiple psychiatric disorders,” says Anttila. “This hints that there is some deeper mechanism underlying multiple disorders.”

This is the largest genetic study of its kind, and the first to show common variants appearing across so many mental health conditions. “It’s a really interesting paper, and I think it’s going to be one of the landmark studies for the future,” says Heather Whalley, a psychiatry researcher at the University of Edinburgh, UK, who was not involved in the study.

It’s still not clear how big a role the shared genes play. It might be that other genes that aren’t shared play a bigger role, says Whalley. And environmental risk factors will also contribute.

Still, the idea that there are measurable physiological factors associated with many mental health conditions at once could address a long-standing issue in psychiatry: that there are few objective measures to diagnose mental illness, unlike other branches of medicine. “We’re relying on subjective experiences of patients,” says Whalley.

She says symptoms can overlap across distinct conditions, and two people diagnosed with the same illness can have no overlapping symptoms. “We don’t know whether this overlap is because our diagnoses are too broad, or that the conditions are associated,” she says. The study suggests the latter is the case.

The findings also hint at a common biological cause underlying mental health conditions. “This is very exciting news,” says Anttila. “The underlying mechanism is there to be caught.”