海明威的父亲（左）、两个兄弟和他本人（中）都自杀身亡
对于很多家族自杀行为频现的问题，科学家一直试图给出合理的解释。根据英国《卫报》11月14日报道，美国科学家经过研究发现，自杀行为或许源于某种特殊的基因。
这项研究成果是在近日举行的神经科学学会大会上发布的。一个由纽约州立精神病研究所首席神经学家约翰·曼恩领衔的科研团队对412名患有严重抑郁症的白人患者进行了基因测试，其中154名受试者都曾尝试自杀。结果显示，在那些曾经尝试自杀的受试者中，超过六成人体内都存在某种RGS2基因的变体。RGS2基因能影响人体感觉器官对神经细胞释放的化学物质的反应。
曼恩表示，虽然目前的研究还不能得出一个确凿的结论，不过从基因方面解释自杀行为的大方向是正确的：“造成人类自杀的应该是一系列的基因，而我们只要找到这些基因，就可以制订出用于判定抑郁症患者是否有自杀倾向的方法……（这样一来）就可以改进我们对抑郁症患者的照顾。”
此前对双胞胎和被收养儿童的研究表明，一个人自杀可能性的约一半是由基因决定的，而这就解释了为什么在某些家族中自杀会呈现遗传性的特征。最著名的案例莫过于著名作家海明威和涅磐乐队主唱科特·柯本：海明威的父亲、兄弟、孙女及其本人均系自杀身亡；柯本的两个叔父死于自杀，柯本本人在1994年自杀前也曾提起，他感觉自己继承了“自杀基因”。
不过，寻找自杀基因的一大难题就在于，难以区分导致自杀与抑郁症的不同基因。曼恩在接受《卫报》采访时称：“大多数自杀者都患有抑郁症，但大多数抑郁症患者从未试图自杀。一些人本来就具有自杀的倾向，只不过是患了抑郁症之后才显现出来。我们可以看到，一些家庭的同辈人中很多都患有抑郁症，但是没有一起自杀案例，而另外一些家庭自杀人数就很多。自杀的遗传性与抑郁症无关。”
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."
