In short, we could hypothesize that the MTHFR C677T allele is a risk factor for the thinning of CT of MDD patients in the left cACC, ISTC, mOFC, and PCC; the C677T homozygote is a protective factor for increased lOFC CT and also allows the volume of the putamen to manifest a decreasing trend in depression. The gene discussed is MTHFR; the disease is major depressive disorder.