MR analyses using methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism as an instrument variable have been carried out in the past11, 13, 14, 15.The researchers provided evidence from MR that plasma Hcy level is causally related to stroke, schizophrenia, T2D and offspring birth weight. Here, MTHFR is linked to type 2 diabetes mellitus.