MTHFR and type 2 diabetes mellitus: In patients with diabetes for >5 years, the frequencies of the CT and TT genotypes and the T allele of the MTHFR C677T locus, and the frequency of the CC genotype of the MTHFR A1298C locus were higher in patients with T2DM and CVD, but there were no significant differences between these two groups (Table 8).