In conclusion, we have performed EWAS of depression symptomatology score in a unique cohort of elderly monozygotic twins and identified blood methylation levels at KLK8, DAZAP2, MAD1L1, SLC29A2, AKT1, and other genes, as well as several DMRs across the genome to be associated with this trait. This evidence concerns the gene KLK8 and major depressive disorder.