MTHFR and type 2 diabetes mellitus: Meta-analysis of all included studies indicated that the genotype at MTHFR polymorphism rs1801133 was not consistently associated with either increased or reduced risk of T2DM across the genetic models tested: the OR across all studies was 0.91 (95%CI 0.82 to 1.00) for the C- vs. T-allele (Fig. 2), 0.88 (0.75 to 1.03) for CC vs. CT+TT, 0.82 (0.71 to 0.95) for CC vs. TT, and 1.15 (1.03 to 1.29) for TT vs. CC+CT (Table 2).