COMT and major depressive disorder: Recently, using diffusion tensor imaging (DTI) technique and tract-based spatial statistics (TBSS) method, many researches have focused on the interaction effect between risk genes and abnormalities of white matter (WM) integrity or fiber tracts in MDD, such as 5-HTTLPR heterozygotes (42, 43), BDNF-met carriers (44), SLC6A15-A carriers (45), NTRK2 homozygous A (46), FKBP5-T carriers (47), COMT homozygous G (48, 49), VMAT1 Thr136Ile-A carriers (50), THP2 homozygous G (51), RERE homozygous T (52).