FNDC5 and obesity due to melanocortin 4 receptor deficiency: Irisin, a peptide hormone, is secreted by skeletal muscle and adipose tissue in response to exercise due to proteolytic breakdown of fibronectin type III (FNDC5), a transmembrane protein.9 It has been postulated that irisin improves pro-oxidant-antioxidant balance by increasing mitochondrial enzymes expression.6 Recently, Irisin has gained great interest as potential target to combat diabetes, obesity and various metabolic disorders associated with these diseases.