In an effort to further delineate the effects of the KLF11–MAOA pathway in anxiety and affective disorders, KLF11 promoter methylation was analyzed via pyrosequencing of sodium bisulfite-treated DNA isolated from human peripheral blood in two independent samples of PD patients with or without comorbid MDD in a case–control design (sample 1: N = 120) as well as MDD patients with and without anxious depression (sample 2: N = 170). This evidence concerns the gene KLF11 and major depressive disorder.