FNDC5 and obesity due to melanocortin 4 receptor deficiency: Irisin, derived from cleavage of FNDC5, has been linked to the beiging of WAT in rodents; however, human data on circulating irisin levels remain highly variable, casting doubt on its relevance to local lipid partitioning in skeletal muscle or connective tissues in obesity and T2DM [198,199,200].