Association of DAO and G72(DAOA)/G30 genes with bipolar affective disorder

There is growing evidence of partial aetiological overlap between schizophrenia and bipolar disorder (BP) from linkage analysis, genetic epidemiology and molecular genetics studies. In the present study we investigated whether individual polymorphisms or haplotypes of the DAO and G72(DAOA)/G30 genes, which have been previously implicated in schizophrenia, are also associated with bipolar disorder. For each gene, we genotyped 213 cases and 197 controls for SNPs previously associated with schizophrenia: rs2111902 (MDAAO-4), rs3918346 (MDAAO-5), rs3741775 (MDAAO-6) and rs3918347 (MDAAO-7) in DAO and rs746187 (M7), rs3916966 (M13), rs2391191 (M15) and rs3916972 (M25) in G72. Although none of the individual SNPs in these genes reached statistical significance, we found haplotype wise associations with bipolar disorder for both genes. These included a two-SNP haplotype in DAO (rs2111902-A and rs3918346-T; global P = 0.003, individual P = 0.002, Z = 3.1) and a two-SNP haplotype for G72(DAOA)/G30 (rs746187-G and rs3916972-G; global P = 0.05; individual P = 0.005, Z = 2.81). However, we found no evidence for an epistatic interaction between the SNPs and/or haplotypes of the two genes. In summary, our findings provide some support for the individual involvement of DAO and G72(DAOA)/G30 in the etiology of bipolar disorder.