In the largest genetic study of its kind, scientists have identified more than 200 genes associated with depression that could give new insights to researchers looking for treatments to what is the leading cause of disability in the world.

Combining anonymous data from more than two million people who were part of the three different genome-wide association studies on depression, an international team of researchers led by scientists at the University of Edinburgh, identified 269 genes associated with depression.

“These findings are further evidence that depression is partly down to our genetics,” said Professor Andrew McIntosh, of the University of Edinburgh’s Centre for Clinical Brain Sciences, who led the research. “We hope the findings will help us understand why some people are more at risk of depression than others, and how we might help people living with depression and anxiety more effectively in the future.”

Published in journal Nature Neuroscience, the study, which included data from the UK Biobank, 23andMe, and the Psychiatry Genomics Consortium, found that many of the strongest associations were on or near genes involved in neurotransmission and response to stimuli that are part of the central nervous system. And the associations further highlight the importance of studying cortical regions of the brain and their role in the condition, according to the researchers.

Trauma, social factors, and life events all play a role in depression, but by understanding the influence genes have and their role in how an individual responds to those external factors, could help in developing more personalized treatments, the researchers said.

This study also found that depression shared genetic associations with neuroticism — a personality type that is characterized as being more fearful and worried. Researchers also found a shared genetic association with smoking. The later association may indicate that depression could lead some people to smoke.