MC4R and obesity due to melanocortin 4 receptor deficiency: Mc4r KO mice exhibited obesity, hyperphagia, hyperglycaemia and hyperinsulinemia8, 21, while Mc3r KO mice displayed almost the same body weight as WT control up to 26 weeks of age, but they did exhibit a mild obesity phenotype characterized by increased fat mass, reduced lean mass and reduced body length16.