MTHFR and type 2 diabetes mellitus: Numerous studies have investigated genetic risk and protective factors for DPN in T2DM in particular, highlighting a potential association with specific polymorphisms in genes including ACE (114), AKR1B1 (115), ADRA2B (116), APOE (117–119), GPx-1 (120), IL-4 (121), IL-10 (122), IFN-γ (122), MTHFR (123), NOS1AP (124), NOS3 (125–127), TLR4 (128), UCP2 (129), and VEGF (Table 2) (130).