Lack of association between bipolar disorder and tyrosine hydroxylase: a meta-analysis

Tyrosine hydroxylase (TH) is a candidate gene extensively explored in several association studies of bipolar disorder (BD). However, because of conflicting results of independent studies and low statistical power of individual studies to detect small differences between cases and controls, reliable conclusions are difficult to formulate. A method to obtain more reliable conclusions about the involvement of the TH locus in the etiology of BD is meta-analysis. We undertook a meta-analysis of studies that investigated the association between BD and TH genetic markers. The studies were identified by means of computerized searches of several databases, and the scanning of review articles and the reference lists of the primary articles identified. More than 60 publications were reviewed, and 9 relevant articles were included in this meta-analysis, with an overall sample of 1,069 subjects (547 cases and 522 normal controls). The overall odds ratio (and confidence interval) based on combining the results of the studies was 1.02 (0.68-1.54). Test of the null hypothesis that the mean log odds ratio equals zero (chi2 = 0.11; 5 df; P > 0.05) indicated that there was no overall association between bipolar disorder and tyrosine hydroxylase.