Association between suicide attempt and a tri-allelic functional polymorphism in serotonin transporter gene promoter in Chinese patients with schizophrenia

Mounting evidence supports the association between a polymorphism in the serotonin transporter gene promoter region (5-HTTLPR) and suicidal behaviour. Recently, a novel variant of the 5-HTTLPR L allele was identified. The previously unknown L _G allele produced similar levels of gene expression to the S allele and might have been misclassified as a " high-expression" allele in previous association studies. In this study, we aimed to compare the genotype distribution of the tri-allelic 5-HTTLPR polymorphism in 168 Chinese patients with schizophrenia, including 60 suicide attempters and 108 non-suicide attempters. In our analysis, which used the L _A dominant model, it was found that the L _A allele carriers were significantly more likely to have attempted suicide (p=0.035). Further analysis showed this association existed only in male patients (p=0.012). A similar association between the L _A allele and violent suicide attempt was also found (p=0.028). In addition, logistic regression confirmed our findings that male L _A allele carriers were at a higher risk of suicide, although the lack of a significant association in females may reflect insufficient power due to small sample size. However, no association was found when we examined the traditional bi-allelic 5-HTTLPR. These findings differ from those reported in Caucasian subjects, where no associations have been reported. Different genetic backgrounds may give rise to different allelic distribution, causing differential effects on the expression of endophenotypes of suicide behaviours. Although the potential influence of multiple comparisons might weaken our findings, our study provides preliminary evidence for a potentially gender-specific role of a " high-expression" 5-HTTLPR polymorphism in susceptibility to suicide in Chinese patients with schizophrenia.