SLC6A4 and major depressive disorder: Several studies support our findings, reporting no association between SLC6A4 methylation in blood and depression in adults, in either Caucasian [12] or three Asian (n = 108; n = 286; n = 100) [14, 15, 17] populations, as well as in buccal mucosa from Caucasian adolescents (n = 150) [16] and EBV-transformed lymphoblasts (n = 192) [18].