Study confirms genetic link to depression

A common genetic variation increases the chances of depression after stressful life events, Australian researchers have confirmed. The study, published in the British Journal of Psychiatry, shows that people who inherit two 'short' versions of a gene that affects the brain chemical serotonin have a high risk of becoming depressed following three or more stressful events in a year. In contrast, people who inherit two 'long' versions of the gene are much less likely to become depressed under the same circumstances, according to the University of New South Wales team.

Scientists based at Kings College in London showed three years ago that people who inherit two short versions of the 5-hyroxy-tryptamine (5-HTT) gene, one from each parent, are more likely to develop serious depression after a stressful life event. The 5-HTT gene makes the serotonin transporter protein, which affects levels of the brain chemical serotonin - low levels of which are linked to depression. In the latest study, the scientists identified a 'tipping point' for the onset of the condition - the risk of the illness developing in susceptible people greatly increases in the wake of a series of stressful events during the course of a year.

The researchers looked at DNA samples from 127 people who are part of a long-term study looking at mental health. They have been monitored for over 25 years, and at five-yearly intervals scientists have recorded any major life events and signs of depression. They found that 80 per cent of those with two short 5-HTT genes became depressed after three or more negative life events in a year, whereas those with two long genes appeared resilient - only 30 per cent developed the illness in similar situations. People who had inherited one long and one short version of the gene had an intermediate risk of becoming depressed.

Around a fifth of the population have this type of genetic predisposition to depression, while a quarter are protected by their genetic make-up. Team leader Peter Schofield said the results were significant because it had 'social, psychological and genetic aspects' to it, adding 'while there is plenty of evidence surrounding the significance of family history of depression, until now there has been very little idea about the specific genes involved'.

Study author Kay Wilhelm said the study had 'very significant implications', such as the potential for reducing depression amongst genetically vulnerable people. 'Eventually you might be able to better identify those who are likely to be at risk, suggest psychological treatment at times, and even work out the best kind of antidepressant to use, if the need arises', she suggests.