To our knowledge, this is the first study to examine associations between (a) 5-HT1A promoter genotype, childhood and recent life stress and (b) blood mononuclear cell DNA methylation and 5-HT1A binding potential in brain, in order to better understand the role of 5-HT1A binding as it relates to effects of stress on MDD. Here, HTR1A is linked to major depressive disorder.