TCF7L2 and obesity due to melanocortin 4 receptor deficiency: The authors con-cluded that dietary vitamin B12 supplementation (alone or combined with folic acid) may be able to regulate several metabolically important genes linked to Type 2 diabetes (T2D), not only through the differential methylation of the fat mass and obesity-associated (FTO) and transcription factor 7-like 2 (TCF7L2) genes, but also through hypermethylation of a genetic region near the microRNA 21 promoter, providing a novel epigenetic interpretation for the correlation between disturbed carbon 1 (C1) metabolism and the risk of obesity, insulin resistance, and T2D [42].