Compared with healthy controls, plasma FGF21 concentrations are markedly increased in IPAH and HPH patients [115,139] as well as increased in rodent MCT-, hypoxia- and Sugen/hypoxia-induced PH models [115], and the vascular remodeling of hypoxia-induced PH can be attenuated by exogenous administration of FGF21 and exacerbated in FGF21 knockout mice [21,140], indicating that FGF21 may be a protective factor against PH. The gene discussed is FGF21; the disease is idiopathic pulmonary arterial hypertension.