INSIG2 and obesity due to melanocortin 4 receptor deficiency: Numerous SNPs identified as susceptibility genomic biomarkers for obesity are indeed found in more or less extensive phenotypes of obesity as BMI, adiposity traits, adipogenesis, lipid metabolism, insulin secretion, and genes involved in neuro-circuits of appetite and satiety, such as BDNF, NEGR, IRS1, and INSIG2 [65,67,68,69,70,71].