INS and obesity due to melanocortin 4 receptor deficiency: While many variants have been identified in PPAR-γ2 gene, the most prevalent and best studied is the Pro12Ala polymorphism which has been shown to impair the function of the PPAR-γ2 isoform of the receptor and to be associated with obesity and/or diabetes and insulin sensitivity related phenotypes in different populations [9, 12, 13].