The PGC GWAS mega-analysis of 9,240 MDD cases and 9,519 controls (replication in 6,783 MDD cases) revealed no findings of genome-wide significance. 108 These null results are intriguing as almost all other published GWAS with N>11,000 for any disease has found at least one genome-wide significant finding. The most likely reasons for these results are particularly high heterogeneity of MDD and insufficient power arising from its lower heritability. 108 There are few published data on SV although one study found increased SV burden in MDD cases versus controls (OR=1.31). 109
