LEP and obesity due to melanocortin 4 receptor deficiency: In particular, the obese ob/ob mouse, mutant for the leptin (OB hormone) gene, is currently used to evaluate the pathogenesis of human obesity and type 2 diabetes: it lacks the functional leptin, develops hyperphagia, insulin resistance, hyperglycemia and hypercholesterolemia together altered immune response, impaired locomotor activity and fertility [1].