Alterations of DNA methylation, a common epigenetic modification, have also been identified in genes involved in various metabolic pathways, such as Pparγ [41], Pgc1α [42,43], leptin [36,44], Lpl and aP2 [41], etc. We have also reported that epigenetic regulation by DNA methylation plays a critical role in modulating various metabolic pathways, including neuronal control of energy metabolism in obesity, macrophage polarization and inflammation in type 2 diabetes and atherosclerosis, and adipocyte differentiation [24,25,31,45,46,47]. The gene discussed is LEP; the disease is type 2 diabetes mellitus.