21 July 2003
ByAppeared in BioNews 217
How well people cope with stressful experiences such as divorce or unemployment is partly down to variations in a single gene, according to a new study by researchers based in the UK, US and New Zealand. The scientists, who published their findings in last week's Science, found that different versions of a gene called 5-HTT can affect a person's susceptibility to serious depression. 'We are not reporting a gene that causes a disease' said team leader Terrie Moffitt, of the Institute of Psychiatry, Kings College London. 'Instead, we believe the gene helps influence whether people are resistant to the negative psychological effects of the unavoidable stresses of life'.
The team looked at a group of 847 people born between April 1972 and March 1973 in Dunedin, New Zealand, who have been tracked since birth as part of a long-term health study. They asked the participants how many stressful events - such as divorce, bereavement and unemployment - they had experienced between the ages of 21-26, and whether they had been affected by depression during that period. The researchers then determined which versions of the 5-HTT gene they had inherited: either the 'long' or 'short' form, or one of each. They found that 43 per cent of the people who inherited two short versions of 5-HTT (one from each parent) developed serious depression after a stressful experience, whereas only 17 per cent of the people who inherited two longer versions of the gene were affected by the illness.
The 5-HTT gene codes for the serotonin transporter, a protein involved in regulating levels of the brain chemical serotonin. Previous studies have shown that animals with two long forms of the 5-HTT gene are better at coping with stressful situations, but this is the first time such a link has been conclusively demonstrated in humans. Moffit thinks that earlier attempts to look for these 'vulnerability' genes have been unsuccessful because such studies fail to take into account environmental exposure. She compared it to looking for malaria susceptibility in a sample that includes people who live in mosquito-free places.
Serious depression, the symptoms of which include persistent sadness and lethargy, is thought to affect around 121 million people worldwide. Moffitt says that the gene variants will probably not be a good diagnostic tool for depression, because the short form is so common in the population. But she thinks that the combination of stressful experiences and genetic susceptibility could help identify people at risk of the condition. 'The most exciting thing about this research is that we've found that the risk of depression is halved for people who have the long-long genes' she told BBC News Online, adding that 'it would be really wonderful if there was a way of preventing it'.