FNDC5 and Duchenne muscular dystrophy: While the precise composition of myokines from dystrophic muscle remains to be fully elucidated, several myokines have been implicated in modulating bone turnover in DMD, including receptor activator of nuclear factor к B ligand (RANKL), fibroblast growth factor (FGF) 21, myostatin, lipocalin 2, and irisin (62).