Tuesday , 22, October 2013 Leave a comment

Separated by time and circumstance, brothers Paul and Jim will spend their entirety of their lives never knowing the other existed.

The two will meet different people and encounter different challenges. They’ll find the passions that inspire them, the tics that annoy them and the losses that break them. And when Jim is 26, he will take his own life.

That very fact alone could tie the two unknown siblings in a way we never expected, according to a new study released on Plos-One last week. Jim’s suicide might mean Paul carries a higher risk of committing his own.

The question of whether genetic factors could predispose someone to suicide is one that researchers have collectively spent decades trying to decipher. And in that sense, this latest study, released by Danish scientists, is more another brick in the mortar than a smoking gun.

Pulling apart some-2000 adoptees whose information was collected through the Danish Adoption Register, the researchers examined the incidence rate of suicide of their siblings, both biological and adoptive.

Among the specifically chosen 221 adoptees who were adopted early and committed suicide before 2006, the suicide rate of their biological siblings was substantially higher than those siblings who were either adoptive or had no suicidal sibling. As much as five to eight times higher. Of those whose foster brother/sister committed suicide, exactly zero of these adoptive siblings went on to commit their own (the authors warn not to read too much into that though).

One of the other major takeaways is the association of suicide remaining there even after removing the factor of psychiatric admissions. This, as the researchers note, is a crude measure of underlying mental illness, but suggests that suicide risk might be independent of mental illness risk, as opposed to the latter influencing the former, as some studies suggest.

Also of interest is the fact the suicide rate was nearly as high between full siblings as it was between half-siblings on the mother’s side, while paternal half-siblings had little increased risk. This ties to similar research showing the same.

As always, the value of absolute numbers is important to keep in mind. Of the 117 people whose biological sibling committed suicide, only four went on to do the same. This is still much higher a rate than those without any suicidal siblings, but again, important to keep in mind. This study, for obvious reasons, also has little to say about attempted suicides or those who face a lifelong battle with suicide ideation.

Still, the Danish study is yet another piece of the puzzle in understanding suicide. Other studies looking at populations of twins or families have found the same shared risk and there’s even been recent work in identifying a specific gene mutation common to suicide victims; work that could someday lead to identifying or even treating so-called presuicidal people, much like we do with various cancers.

The myriad of risk factors which can push someone to take their own life should never be underscored though, nor studies like this distract us from learning how best to help people struggling in the here and now with suicidal thoughts. As the Jims of the world go, the least we can do is to understand their tragic paths.

Genetic and Familial Environmental Effects on Suicide – An Adoption Study of Siblings

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