Meta-analysis Report

Reference	Chen, D.,2011 PMID: 21601290
Citation	Chen, D., F. Liu, et al. (2011). "Association between the TPH1 A218C polymorphism and risk of mood disorders and alcohol dependence: Evidence from the current studies." J Affect Disord.
Disease Type	Bipolar Disorder & Major Depressive Disorder
Study Type	Candidate-gene association study

Samples	Twenty-seven individual studies were included in the current study, among which, there were 9 studies for bipolar disorder, with 1951 cases and 2161 controls, 14 studies for major depressive disorder, with 2340 cases and 3204 controls, and 4 studies for alcohol dependence, with 601 cases and 711 controls.
Statistic Method	In the analysis of pooled data, the between-study heterogeneity was investigated by using the Cochran's Q test, and the heterogeneity was considered significant if P <0.05 (Yin et al., 2010). In addition, the I2 metrics was also used to determine the impact of heterogeneity,and the following suggested cutoff points were used:Pooled ORs and 95% CIs were calculated by using fixed effect model when the heterogeneity was negligible or random effect model when the heterogeneity was significantly presented. To test publication bias, the funnel plot and Egger's test (liner regression analysis) were used (Egger et al., 1997). The significance of pooled OR was determined by the Z-test and the P values were adjusted using conservative Bonferroni correction for multiple testing for 3 disorders and subgroup analyses, but nominal P values were also shown. All analyses were done with Stata Statistical Package (version 10.0).
Basic Result	We found that in Caucasian population, the TPH1 218AA genotype was significantly associated with increased bipolar disorder risk (recessive comparison: OR, 1.42; Bonferroni-adjusted P=0.006; homozygote comparison: OR, 1.63; Bonferroni-adjusted P=0.072), and elevated alcohol dependence risk (recessive comparison: OR, 1.83; Bonferroni-adjusted P=0.012), while the association was not significant in Asian population. Moreover, the A218C polymorphism did not appear to have any effect on major depressive disorder risk either in Caucasians or in Asians. CONCLUSION: The TPH1 A218C polymorphism is a potential biomarker for bipolar disorder and alcohol dependence risk in Caucasian population.