The role of TGFβ proteins in muscle wasting in PAH has not been widely analysed, being limited to one study showing increased circulating myostatin in MCT-treated rats.29 We have identified, as is the case in ICUAW,12 COPD14 and cancer,30 that PAH-associated muscle loss may also be a GDF-15 driven phenomenon. The gene discussed is MSTN; the disease is pulmonary arterial hypertension.