GWAS methods evaluate the contribution of common single nucleotide polymorphisms (SNPs) to common diseases. They have identified robust associations to many non-psychiatric disorders10 and to bipolar disorder11, schizophrenia12–14 and autism.15 No genome-wide significant findings were reported for GAIN-MDD5 or GenRED4, or for a GWAS (not included in this meta-analysis) of 1,514 recurrent MDD cases and 2,052 controls (without lifetime depressive or anxiety disorders) from a German clinical sample and a Swiss population-based sample.16 This is not surprising, as most GWAS findings have emerged when multiple datasets were combined to achieve large sample sizes (often 10,000–20,000 cases plus controls) with power to detect variants that produce small increases in risk.10 We have reported separate GenRED and STAR*D analyses, because their distinctive characteristics could prove relevant to interpreting results across studies in the future, but to achieve a larger sample size we also report a meta-analysis of STAR*D, GenRED and GAIN-MDD data.
