FNDC5 and obesity due to melanocortin 4 receptor deficiency: In addition to its beneficial effect on obesity, irisin has also been linked to positive effects on many other diseases in which exercise is beneficial, including type 2 diabetes mellitus (T2DM) (16, 17), cardiovascular disease (CVD) (18), nonalcoholic fatty liver disease (NAFLD) (19), Alzheimer’s disease (20), and metabolic bone diseases (15).