SLC6A4 and major depressive disorder: Interestingly, our previous study of SERT clusters in depression demonstrated that although patients in both the D-I and D-II groups showed a significant response after 8 weeks of pharmacological treatment (as measured by the HDRS), the patients in the D-II group showed a better response than those in the D-I group, with 3⁄4 of D-II patients showing remission of symptoms [11].