Liu and co-workers found significantly lower level of circulating irisin in long-term type 2 diabetes patients compared with non-diabetic controls [8]; and the lower serum irisin was also found in new-onset by Choi et al. [9] and undefined type 2 dibetes patients by Moreno-Navarrete et al., respectively [10]. Here, FNDC5 is linked to type 2 diabetes mellitus.