A new University of Colorado Boulder study assessing genetic and survey data from 620,000 individuals found that the 18 most highly-studied candidate genes for depression are actually no more associated with it than randomly chosen genes.
Everyone experiences some unhappiness, often as a result of a change, either in the form of a setback or a loss, or simply, as Freud said, “everyday misery.” The painful feelings that accompany these events are usually appropriate, necessary, and transitory, and can even present an opportunity for personal growth.
Depressionaffects approximately 322 million people worldwide, making it the largest contributor to global disability. Scientists have discovered many genetic markers linked to the development of major depressive disorder, any may were used as the basis for drug research rather than investigating alternatives.
Over the past quarter-century, researchers have published hundreds of studies suggesting a small set of particular genes or gene-variants plays a substantial role in boosting susceptibility to depression. Such papers fueled hopes that clinicians could soon use genetic testing to simply identify those at risk, and drug companies could develop medications to counteract a few genetically-driven culprits.
The previous studies were incorrect– or “false positives”–and the scientific community should abandon what are known as “candidate gene hypotheses,” the authors conclude.
“This study confirms that efforts to find a single gene or handful of genes which determine depression are doomed to fail,” said lead author Richard Border, a graduate student and researcher at theÂ Institute for Behavioral Genetics.
Adds senior author Matthew Keller, an associate professor of Psychology and Neuroscience: “We are not saying that depression is not heritable at all. It is. What we are saying is that depression is influenced by many many variants, and individually each of those has a miniscule effect.”
For the study, published in theÂ American Journal of Psychiatry, the authors looked at 18 genes which have appeared at least 10 times in depression-focused studies. Among them was a gene called SLC6A4, involved in the transport of the neurochemical serotonin. Research dating back 20 years suggests that people with a certain “short” version of the gene are at significantly greater risk of depression, particularly when exposed to early life trauma.