MTHFR and major depressive disorder: Therefore, in the present study, we enrolled highly homogeneous MDD patients, evaluated the efficacy of antidepressant therapy at 6 weeks response (primary endpoint) and 8 weeks remission (second endpoint) after received a single antidepressant drug, intended to confirm the association of MTHFR, ApoE and ApoA4 with MDD and antidepressant response.