Full sample details are given in the Supplementary Methods. For the discovery phase, we included all identified primary MDD samples21–25,27,28,41 that conducted genome-wide genotyping (> 200K single-nucleotide polymorphisms (SNPs)) on individual subjects of European ancestry. Cases were required to have diagnoses of DSM-IV lifetime MDD established using structured diagnostic instruments from direct interviews by trained interviewers (two studies required recurrent MDD and one recurrent, early-onset MDD) or clinician-administered DSM-IV checklists. Most studies ascertained cases from clinical sources, and most controls were randomly selected from the population and screened for lifetime history of MDD. The sample sizes reported here differ from the primary reports due to different quality control procedures and apportioning of overlapping controls. We determined the relatedness of all pairs of individuals using genotypes of SNPs present on all platforms, and excluded one of each duplicate or closely related pair. The discovery mega-analysis consists of 18 759 independent and unrelated subjects of recent European ancestry (9240 MDD cases and 9519 controls).
