In conclusion, a meta-analysis of three GWAS datasets did not detect genome-wide significant evidence for association to MDD. Of the best-supported genes and regions, GRM7 has the greatest previous biological support for involvement in processes such as mediation of response to antidepressant and antimanic drugs. It is likely that much larger samples will be required to clarify the role of common SNPs in genetic susceptibility to MDD. We are participating in the efforts of the Psychiatric GWAS Consortium44, 63 to carry out meta-analyses incorporating additional samples. Given the moderate heritability and clinical heterogeneity of MDD, larger samples with careful phenotypic characterization would be useful.
