STin2 Variant and Family History of Suicide as Significant Predictors of Suicide Completion in Major Depression

Background Suicide is the most serious outcome of major depression, yet not all depressed patients will commit suicide. Genes, along with other factors, might account for this difference. Serotonergic alterations have been observed in suicide and depression and impulsive-aggressive behaviors. Therefore, we aimed to identify predictors of suicide, considering genetic variation at the serotonin transporter (5-HTT) gene. Methods We investigated the 5-HTT gene-linked polymorphic region (5-HTTLPR) and intron 2 (STin2) variants of this gene and their relationship to behavioral and clinical risk factors for suicide in a sample of depressed suicides (n =106) and depressed control subjects (n =152), diagnosed by means of proxy-based interviews. Results We found a significant association of suicide completion with having at least one copy of the STin2 10 allele [χ2(1) = 10.833, p = .002]. No differences were found for the 5-HTTLPR variable number of tandem repeats. After controlling for behavioral and clinical risk factors for suicide, the STin2 variant remained a significant predictor of suicide in major depression when jointly considered with a family history of suicide (odds ratio 5.560, 95% confidence interval 1.057–29.247). Conclusions The STin2 locus might account, at least in part, for the observed familial aggregation of suicidal behavior. These results should be further explored in families where clustering of suicidal behavior is observed.