INS and obesity due to melanocortin 4 receptor deficiency: Contemporary research on the epigenetics of obesity is based on three fundamental mechanisms: DNA methylation, which regulates the expression of key metabolic genes through modification of cytosines primarily located in CpG islands of gene promoters; microRNAs, which mediate post-transcriptional regulation of genes involved in adipogenesis and insulin signaling; and chromatin modifications, including histone marks and remodeling complexes that determine the accessibility of genomic loci (Figure 1) [5,6,7].