Genetic association between the dopamine D3 gene polymorphism (Ser9Gly) and schizophrenia in Japanese populations: evidence from a case-control study and meta-analysis.

Dysregulation in the dopaminergic system has been implicated in the pathophysiology of schizophrenia (SCZ). Dopamine D3 receptors (DRD3) concentrated in limbic regions of the brain (important for cognitive, emotional and endocrine function) may be particularly relevant to SCZ. A recent meta-analysis with mixed ethnicities reported a marginal significant association between the Ser9Gly homozygosity in the first exon of the DRD3 gene and SCZ. To further evaluate the controversial association between this polymorphism and SCZ, a case-control study and meta-analysis was conducted using the homogeneous Japanese population. In our Japanese case-control sample (246 cases/198 controls), we found an association between the DRD3 Ser9Gly polymorphism and SCZ (genotype: chi(2) = 9.76, d.f. = 2, p = 0.008; Ser allele versus Gly allele: chi(2) = 7.96, d.f. = 1, p = 0.0048; OR = 0.65; 95% CI = 0.48-0.88). However in a meta-analysis of nine Japanese case-control studies comprising 2056 subjects the association between DRD3 Ser9Gly polymorphism and SCZ did not persisted. The Mantel-Haenszel pooled OR for SCZ among carriers of the DRD3 Ser9Gly homozygosity (Ser/Ser homozygotes and Gly/Gly homozygotes) of the nine Japanese studies was 1.16 (95% CI 0.97-1.39), pointing to a non-significant effect of the DRD3 Ser9Gly homozygosity as a risk factor for SCZ. Overall, our results suggest that the DRD3 Ser9Gly polymorphism may not confer susceptibility to SCZ in the Japanese population. Given that the Ser9Gly variant may play a putative role in DRD3 function, further studies on the DRD3 with linked variants are warranted.