Irisin is produced by the proteolytic cleavage of the fibronectin type III domain-containing protein 5 (FNDC5) (Bostrom et al., 2012) and plays a pivotal role in the occurrence and development of obesity, diabetes, non-alcoholic fatty liver disease, and other metabolic diseases (Arias-Loste et al., 2014; Shelbaya et al., 2017; Suk et al., 2018). The gene discussed is FNDC5; the disease is obesity due to melanocortin 4 receptor deficiency.