TCF7L2 and obesity due to melanocortin 4 receptor deficiency: Likewise, according to Yadav et al., dietary vitamin B12 supplementation (either alone or in combination with folic acid) affected the regulation of several metabolically important genes associated with T2D, not only through differential methylation of the FTO and TCF7L2 genes but also through the hypermethylation of a genetic region near the miRNA 21 promoter, providing a new epigenetic explanation for the association between disturbed C1 metabolism and the risk of obesity, insulin resistance, and T2D [52,53].