Depression is one of the most common mental health conditions in the world. In 2014 alone, an estimated 15.7 million American adults reported having at least one depressive episode. Scientists have been saying for decades that depression is a real illness with multiple physiological causes, yet we tend to treat it like it’s a shameful character flaw or a choice. A new study puts another nail in the coffin of that harmful fallacy: Researchers have identified 15 areas of the genome that are significantly more common in people with major depressive disorder (MDD). They published their findings today in the journal Nature Genetics.

MDD, also known as clinical depression, can turn lives upside down. People with depression are not "just sad"; they’re facing down symptoms like fatigue, loss of appetite, physical pain, feelings of hopelessness, and trouble concentrating. Depression can make it very hard to work or engage with loved ones.

The good news is that treatments are available. The bad news is that everyone’s depression is different, and finding the right treatment can take time. Researchers are hard at work learning everything they can about the causes and physiology of depression, because the more we know, the more effective our treatments can become.

We’ve known for a while that depression tends to run in families, but the details of that genetic component have largely remained elusive. One previous study of more than 10,000 Chinese women had already looked into, and found, genetic regions associated with depression, and researchers wanted to know if they might be able to find similar traces in other people.

Fortunately, we’re living in an age of crowd sourcing and quantified everything, when getting your DNA tested is as simple as mailing off a swab covered with your saliva. Millions of people are submitting their samples to testing companies like 23andMe, and many of them have agreed to make their results available to researchers. So the team pulled genetic data on more than 300,000 23andMe users of European descent. Of those volunteers, 75,607 said they’d been diagnosed with or treated for clinical depression.

The researchers then scanned all the participants’ genomes, looking for potential areas of overlap. They found them: 17 genetic variations—specifically, single nucleotide polymorphisms, or SNPs—spread through 15 regions of the DNA of people with depression. Further analysis showed that those 15 regions are hotspots for genes expressed in the nervous system and those associated with brain development. And previous studies have already linked those regions to other mental health issues.

Like its predecessor, this study looked at one specific group of people of similar descent, most of whom were women (62 percent). So while the results are not universal, they nevertheless underscore the crucial role of genetics in mental health.

Roy Perlis is a medical director at the Department of Psychiatry and the Center for Human Genetic Research at Massachusetts General Hospital, as well as co-corresponding author on the paper.

"Identifying genes that affect risk for a disease is a first step toward understanding the disease biology itself, which gives us targets to aim for in developing new treatments," Perlis said in a press statement. "More generally, finding genes associated with depression should help make clear that this is a brain disease, which we hope will decrease the stigma still associated with these kinds of illnesses."

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