Linkage disequilibrium between dopamine D1 receptor gene (DRD1) and bipolar disorder

Based on the dopamine hypothesis, the dopamine D1 receptor gene (DRD1) is considered to be a good candidate gene for bipolar disorder (BP). In our study, three polymorphisms of the DRD1 gene, -800T/C, -48A/G, and 1403T/C, were analyzed in 286 BP trios. Both the transmission disequilibrium test (TDT) and haplotype TDT were performed on the genotype data to test for the presence of linkage disequilibrium between DRD1 and bipolar disorder. With the extended transmission disequilibrium test (ETDT), we also calculated the maternal transmission and paternal transmission for each allele. Although no association was found for each individual polymorphism, there is a significant association between DRD1 and BP for haplotype TDT analysis (χ 2 = 16.068, df = 3, p = .0011). These results indicate that DRD1 may play a role in the etiology of bipolar disorder.