Genes encoding proteins involved in serotonergic metabolism are major candidates in association studies of suicidal behavior. The tryptophan hydroxylase (TPH) gene, which codes for the rate-limiting enzyme of serotonin biosynthesis, is a major candidate gene and has been extensively studied in association studies of suicidal behavior, providing conflicting results. It is difficult to interpret these conflicting results due to lack of power, ethnic heterogeneity, and variations in the sampling strategies (in particular for controls) and in the polymorphism of the TPH gene studied. Meta-analyses can improve the statistical power for the analysis of the effects of candidate vulnerability factors. The analysis of the sources of heterogeneity that contribute to these conflicting results is an important step in the interpretation of these conflicting association results and in the interpretation of the results of a meta-analysis. We selected all of the published association studies between the TPH gene polymorphism and suicidal behavior. Nine association studies between the A218C TPH polymorphism and suicidal behavior fulfilled the inclusion criteria. A significant association was observed between the A218C polymorphism and suicidal behavior using the fixed effect method (odds ratio (OR) = 1.62; 95% confidence interval (CI) = [1.26; 2.07]) and the random effect method (OR = 1.61; 95% CI = [1.11; 2.35]). The analysis of the sources of heterogeneity showed that two studies (one positive and one negative) significantly deviated from the calculated global effect. The meta-analysis performed after removing those two studies also revealed a significant association between the TPH A218C polymorphism and suicidal behavior. Both analyses suggested that the A allele has a dose-dependent effect on the risk of suicidal behavior.
Copyright 2004 Wiley-Liss, Inc.