The maintenance DNA methyltransferase DNMT1 via CpG promoter methylation epigenetically controls the expression of important developmental genes involved in mTORC1 signaling including insulin (INS) [127], IGF-1 (IGF1) [128,129], and fat mass- and obesity-associated gene FTO (FTO) [130]. Here, FTO is linked to obesity due to melanocortin 4 receptor deficiency.