HMOX1 and obesity due to melanocortin 4 receptor deficiency: Therefore, promoter methylation was investigated at these loci, as well as at previously identified gene promoters reported in the literature to be regulated by DNA methylation in response to high-fat diet, obesity or T2D (Leptin, Pparg, Glut4, Fasn, Irs1, Hmox1, Fabp4).