SLC6A4 and major depressive disorder: 5-HTTLPR genotype groups did not differ in SLC6A4 methylation neither for methylation factor 1 (LALA: n = 35, M = 0.06, SD = 1.04; S/LG: n = 91, M = − 0.08, SD = 0.93; t (56.06) = 0.68, p = .50) nor for methylation factor 2 (LALA: n = 35, M = − 0.22, SD = 0.09; S/LG: n = 91, M = 0.09, SD = 1.08; t (73.96) = − 1.62, p = .11) nor for age at depression onset (LALA: M = 26.02, SD = 12.72; S/LG: M = 25.78, SD = 13.44; t (80.49) = 0.11, p = .92).