The gene appears to be more common in depressed people who have attempted suicide than in those who have not

Genetic tests on depressed people who tried to take their own lives have revealed a DNA marker that could help doctors spot patients who are at risk of suicide.

The gene variant was more common in depressed people who had attempted suicide than in those who had not, suggesting that it marks out a group of people who are especially vulnerable if they become depressed.

The gene is among several that might ultimately be used to screen people with serious depression to identify those that need the closest supervision while being treated.

"If we knew who had an enhanced risk of suicide, we could change our approach to their care," said John Mann, chief neuroscientist at the New York State Psychiatric Institute.

"We could warn the family and ask them to be extra vigilant, we could send reminders to people to repeat their prescription, and tell the patient the importance of sticking with their treatment," he said.

Previous studies of twins and people who were adopted show that around half a person's risk of suicide is due to genetic factors. The heritability of suicidal tendencies can explain tragic clusters of deaths in families, such as those that blighted Ernest Hemingway's and Kurt Cobain's families.

Hemingway's father killed himself in 1928. Hemingway himself attempted suicide in the spring of 1961, and succeeded in the summer of that year. Two of his siblings and his granddaughter also took their own lives. Two of Cobain's uncles took their own lives. Before killing himself in 1994, Cobain said he felt he had inherited "suicidal genes".

Despite clear evidence that suicidal behaviour can run in families, scientists have struggled to find which genes are involved. Part of the difficulty has been distinguishing gene variants for suicide risk from those that put people at risk of depression.

In work described at the Society for Neuroscience meeting in Washington DC, Dr Mann conducted genetic tests on 412 Caucasians with major depression, 154 of whom had attempted suicide. The results revealed a variant of a gene called RGS2 that appeared more often in those who tried to kill themselves. The gene affects how strongly receptors in the body respond to chemicals released by nerve cells.

Mann showed that 43% of the depressed patients who had attempted suicide had two copies of a particular variant of the RGS2 gene, while fewer than a fifth of them had two copies of a "safer" variant of the gene. Mann said further studies were needed to confirm the research, which has yet to be peer-reviewed.

"It will be a panel of genes that will contribute to this, and if we can identify those genes, that panel could be used as a screening tool to predict the risk of suicidal behaviour in depressed patients," Mann told the Guardian.

"People with depression account for most suicides, but most people with depression never make a suicide attempt. There is a vulnerability for suicidal behaviour in some individuals and it is uncovered by the development of depression.

"You'll see some families with lots of depression in each generation but not a single suicide. And other families with quite a few suicides. It's heritable independent of depression."