Decreased KCO was also found in patients with PVOD/PCH with or without biallelic EIF2AK4 mutations.34 Although some reduction in KCO is one of the typical features of pulmonary vascular disease, patients with PVOD show the lowest KCO values when compared with IPAH or chronic thromboembolic pulmonary hypertension. This evidence concerns the gene EIF2AK4 and idiopathic pulmonary arterial hypertension.