FNDC5 and chronic kidney disease: Irisin is a hormone secreted during exercisethat increases energy expenditure by stimulating the expression of UCP-1 and, thus,the "browning" of white adipose tissue.3 Thisnovel hormone has been proposed to be an attractive future therapeutic target formetabolic disorders.1,3,6,7 However, the effects of irisin in humans arestill unclear and, data regarding circulating irisin levels in patients with CKD arestill lacking.