Thus, in the present study, we for the first time examined KLF11 DNA methylation levels in (1) patients with panic disorder in a case–control design taking into account comorbidity with MDD, and (2) in an independent sample of patients with MDD by comparing symptom subtypes (i.e., anxious vs. non-anxious depression) in an effort to for the first time explore the role of KLF11 on an epigenetic level in anxiety and affective disorders. This evidence concerns the gene KLF11 and major depressive disorder.