In this study, our intention was to verify possible associations between the variants of MTHFR, KCNJ11, and UCP2 and indicators of the course of T2D, including pre- and postprandial glycemia, indicators of lipidemia, the rate of metabolic oxidation of biosubstrates, and serum concentrations of homocysteine and vitamins B6, B9, and B12, whose deficiency plays one of the key roles in the development of diabetic polyneuropathy. The gene discussed is MTHFR; the disease is type 2 diabetes mellitus.