FNDC5 and hydrops fetalis: On the other hand, the functional status of HF patients seems to be strongly associated with plasticity of skeletal muscle metabolism, which is simultaneously enhanced by the expression of the peroxisome proliferator-activated receptor-γ (PPARγ) coactivator-1α and the fibronectin type III domain containing 5 (FNDC5) gene, which encodes the production of irisin (Lecker et al., 2012; Tiano et al., 2015).