A new study has identified 44 genetic variants that can heighten the risk of depression.
The National Institute of Mental Health deem major depression "one of the most common mental disorders in the United States."
Around 16.2 million adults had "at least one" episode of major depression in 2016 alone.
Depression has many risk factors — biological, environmental, and of a psychological nature — and often it is a combination of these that leads to the development of the condition.
Of the biological factors, inherited genetic variations are often cited, though researchers have had a hard time in pinpointing which genetic locations in our DNA are specifically linked with a higher risk of depression.
But a large-scale new study has gone where no others have gone before and identified dozens of previously unknown genetic variations that constitute a risk factor for major depression.
The researchers involved in the study — including Dr. Patrick F. Sullivan, at the University of North Carolina School of Medicine in Chapel Hill — note that studies of the human genome focused on risk factors for depression face many obstacles.
In their paper, which is published in the journal Nature Genetics, they write:
"There are many reasons why identifying causal loci for [major depressive disorder] has proven difficult. [Major depressive disorder] is probably influenced by many genetic loci, each with small effects, as are most common diseases, including psychiatric disorders."
Study charts complex genetic risk factors
The researchers managed to access and analyze seven different sets of genetic data, including some sourced from the controversial DIY genetic testing company 23andMe.
These were collected from 135,458 individuals diagnosed with major depression, and 344,901 depression-free controls.
This analysis revealed 44 different genetic variants with a statistically significant impact on individuals' development of major depression.
Of these, 14 had already been linked to depression, but the remaining 30 were previously unknown as risk factors. Moreover, the researchers pinpointed 153 genes that they deemed relevant to the risk of depression.
In terms of risk factor overlaps, the team also found that six of the genetic variants that correlated with a higher risk for depression were at the same time associated with a heightened risk for another psychiatric disorder: schizophrenia.
"This study is a game-changer," Dr. Sullivan explains, continuing, "Figuring out the genetic basis of major depression has been really hard."
"A huge number of researchers across the world collaborated to make this paper," he says, "and we now have a deeper look than ever before into the basis of this awful and impairing human malady."
'New doors opened' for further research
The researchers are well aware that, for depression to take hold, several factors must be present. For example, traumatic life experiences act as a "fertilizer," or a catalyst, for this condition, and it would not be able to take root easily in the absence of a welcoming "soil."
In the case of depression, this soil might be a combination of genetic variations that make a person a lot more susceptible to the disorder.
"We show that we all carry genetic variants for depression, but those with a higher burden are more susceptible," says study co-author Naomi Wray, from the University of Queensland in Brisbane, Australia.
She continues, "We know that many life experiences also contribute to risk of depression, but identifying the genetic factors opens new doors for research into the biological drivers."
The researchers hope that their new findings will spur further studies to develop better treatments targeting the genetic factors involved in depression.
"With more work, we should be able to develop tools important for treatment and even prevention of major depression," says Dr. Sullivan.