We confirmed bilateral hippocampal volume reductions in recurrent depression (F5,381>15.128, p<1.2e-04, N=204, tab. S2) and found a rs1545843 genotype diagnosis interaction effect on both left and right total hippocampal volumes (left: group: case- control, genotypes AA vs. AG/GG: F5,381=5.861, p=0.016, right: F5,381=5.686, p=0.018). Subregional analysis within the hippocampal formation revealed strongest effects for the bilateral cornu ammonis (CA) (left: group: case-control, genotypes AA vs. AG/GG: F5,381=9.512, p=0.002, pcorr<0.05, right: F5,381=5.686, p=0.011, N=204 cases and 186 controls, tab. S2). For rs1081681 which is highly correlated with rs1545843 in the MR morphology sample (r=0.819), diagnosis genotype interaction effects were even stronger with a similar emphasis on the left hemisphere and the CA region (fig. 5 and tab. S2). No genotype or diagnosis genotype effects were observed for either polymorphism for the dentate gyrus and the subiculum of the hippocampus and the control region (precentral gyrus). Hippocampal morphology is a heritable trait (h2=0.4) (Sullivan et al., 2001), nonetheless it is subject to stronger environmental influences compared to other brain regions (Glahn et al., 2007), and interactions between recurrent depression and specific genetic predispositions
