BDNF and depressive disorder: None of these SNPs were associated with average BDNF methylation across promoters I and IV; however, three were found to modify the previously observed association between depression and CpG unit 3.4.5 methylation levels (P-values for interaction term: rs6265, P=0.022, rs7103411, P=0.023 and rs908867, P=0.094).