Major Depressive Disorder (MDD) is the leading cause of disability for adults under 45 years of age1, and has a lifetime incidence of 12–20%.2 Twin studies suggest a heritability of about 40% (perhaps higher in clinical samples), with a 2–3-fold increased risk to first-degree relatives of MDD probands.3 There are no established neurobiological mechanisms or definitive genetic associations. Here, we report on a new genome-wide association study (GWAS) of MDD in the Sequenced Treatment Alternatives to Relieve Depression (STAR*D) sample, and on a meta-analysis of STAR*D and two other datasets: the Genetics of Recurrent Early-Onset Depression (GenRED) GWAS reported in a companion article4; and GAIN-MDD, a dataset that was analyzed in the first MDD GWAS report5 and that has been made available to scientists through the dbGAP (Database of Genotypes and Phenotypes) repository.6
