Therefore, post-exercise irisin production exerts positive effects on the metabolism, and may play a beneficial role in treatment of obesity and obesity-related diseases, type 2 diabetes mellitus (T2DM), or non-alcoholic fatty liver disease (NAFLD) [6], especially since decreased irisin levels accompany obesity, type 2 T2D, and other diseases like chronic renal failure and prolonged hypothyroidism [7]. The gene discussed is FNDC5; the disease is obesity due to melanocortin 4 receptor deficiency.