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Genetics of Suicide

By Richard Violette M.A., Gustavo Turecki M.D., Ph.D., McGill Group for Suicide Studies, Department of Psychiatry, McGill University, Montréal, Québec, Canada, www.douglas.qc.ca/suicide

Debates are still ongoing about the precise causes of suicide, in particular to what extent people are reacting to a situation (e.g. break-up, lost job), or whether there is a built-in biological or genetic explanation as to why people commit suicide. The notion that suicide is in part related to our genetic makeup is not a new idea. Early scientists observed that suicide had a tendency to run in families and affect successive generations. Since then, many studies have confirmed that biological relatives of those who have died by suicide are at increased risk of suicidal behaviour themselves. However, the increased risk is relatively modest when compared to the effect of other risk factors, such as the presence of a psychiatric illness.

While there is strong support for familial and genetic factors increasing vulnerability to suicidal behaviour, it is unlikely that genes have direct effects on suicide itself. Many crucial questions remain, specifically concerning the overlap between the influence of genes on suicide and the genetic predisposition to psychiatric illness. Consequently, researchers over the last decade are more and more focused on exploring this fundamental question in an attempt to disentangle the two. What researchers are increasingly realizing, based on the substantial evidence, is that the underlying genetic predisposition to suicidal behaviour is different, yet at the same time dependent on the genetic transmission of psychiatric illness.

The general idea is that the genetic effects of suicide act through intermediate factors, a sort of go-between, which link genes and suicidal behaviour.  For instance, personality characteristics such as being very impulsive or very anxious are good examples. Both of these so-called personality traits have a genetic component themselves. So, individuals who are genetically predisposed to be very impulsive may, under certain conditions, be at increased risk of suicide. In short, genes are unlikely to directly increase suicide risk. In addition, these genetic effects are complex since the action of some genes may only be obvious when considered in the context of other genes or particular environments.

Rooted in this line of reasoning and based on the understanding that our DNA responds to environmental experiences during life, we have recently begun to learn about mechanisms that help the environment communicate with the genome. Epigenetics is the science that examines these mechanisms, and more specifically, it studies non-heritable factors which influence the expression of genes without altering the DNA sequence itself. Recent studies suggest that such epigenetic changes could influence susceptibility to suicide by altering the systems which regulate how we respond to stress. Exploring these epigenetic effects represents an important bridge in understanding the links between genetic factors on one hand and the environment on the other. And to be sure, identifying these genes and mechanisms could prove instrumental in identifying at risk individuals and preventing suicide in the future.

While there is strong support for a genetic component to increasing vulnerability to suicide, we are still far away from understanding the specific biological and genetic mechanisms which underlie suicide. However, we do know that genes alone are not the direct cause of suicides, yet genetics clearly have an effect.

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