The researchers say their study shows "what might be considered a risk gene for depression in one context may actually be beneficial in another."
The finding challenges a traditional view about the link between genetics and depression, suggest Dr. Chad Bousman and colleagues, from the University of Melbourne in Australia, who report their work in the British Journal of Psychiatry Open.
The traditional view holds that if you carry a version of a gene that is linked to higher risk of depression, then it makes you more vulnerable to depression.
But the new study suggests it is less a case of vulnerability and more a case of plasticity - what deepens the negative may also heighten the positive - as Dr. Bousman explains:
"Our results suggest some people have a genetic makeup that makes them more susceptible to negative environments, but if put in a supportive environment these same people are likely to thrive."
The team of psychiatrists and general practitioners suggests the findings have profound implications for the treatment of depression.
"You can't change your genotype or go back and change your childhood, but you can take steps to modify your current environment," says Dr. Bousman. "It also means that it's not as clear-cut as telling a person that because they have a risk gene, they're doomed. This research is showing that's not the case at all."
First study to examine link between SERT and ongoing severe depressive symptoms
The researchers were interested in finding out why some adults with a history of childhood sexual or physical abuse go on to develop long-term depression.
The study is the first to investigate how a certain gene can influence people's sensitivity to environment by following a group of participants over time.
The gene they investigated is called SERT. It codes for a protein that transports the mood-regulating chemical serotonin.
Each of us has one of three versions of SERT: the long-long (l/l), the short-long (s/l) or the short-short (s/s) version.
For the study, the team analyzed the DNA of 333 middle-aged Australians of Northern and Western European descent and assessed them for symptoms of depression over 5 years using a mental health questionnaire called PHQ-9 (the Primary Care Evaluation of Mental Disorders Patient Health Questionnaire).
The results showed that of the 23% of participants with the s/s version of SERT, those who had a history of childhood abuse were the most likely to experience ongoing severe depressive symptoms in middle age.
However, carriers of the s/s version of SERT who did not have a history of abuse were also the ones whose mental health assessment showed them to be happier than the rest of the participants.
The researchers suggest the gene could be used to assess people's susceptibility to depression, particularly if they have a history of child abuse. It could also help to identify patients who may need extra support.
Dr. Bousman suggests the findings also offer hope to people who experience ongoing clinical depression: genetic makeup is not the only thing that determines how they might experience depression. He concludes:
"This research tells us that what may be considered a risk gene in one context may actually be beneficial in another. So this directly opposes the notion of genetic determinism, the idea that your genes define your fate."
He and his colleagues now plan to extend their research to see if several genes working together also have this effect.
They also point out that their study was limited to participants of Northern and Western European descent, and the findings may not apply to other populations.
Meanwhile, Medical News Today have learned of new research that suggests a healthy diet may reduce the risk of depression. A BMC Medicine study that followed over 15,000 participants for 10 years, led by the University of Las Palmas de Gran Canaria in Spain, found that those who ate lots of fruits, vegetables, nuts and legumes had a reduced risk of developing depression.