Scientists have identified a genetic variation that could make people more susceptible to depression, according to a report published Friday in the New York Times. The study by Duke University researchers could help explain why some people who develop the condition don’t respond to drug treatments.

The findings could result in a genetic test for vulnerability to depression and improved treatments, the newspaper reported, citing research that was published in the online edition of the journal Neuron.

Lead researchers Dr. Marc Caron and Dr. Xiaodong Zhang, biologists at Duke University Medical Center, were part of a team who discovered the mutation of a single gene that reduces the amount of serotonin produced by brain cells. Serotonin is a hormone strongly connected to mood, and higher levels of it in the brain are linked to positive feelings. Low levels are thought to cause Depression.

Widely-used antidepressant drugs like Prozac and Zoloft have a powerful effect on serotonin levels and help regulate moods, experts say.

In a study of 87 people with major Depression, researchers found that 10 percent had the gene mutation - a significant genetic correlation - for a disorder that is influenced by multiple genes, according to the newspaper. Less than 1 percent of a different group without Depression had the mutation.

This is the first gene mutation that directly reduces serotonin levels, which are linked to Depression and other mental troubles, one of the researchers told the paper.