In the largest case series of patients with PAH and biallelic EIF2AK4 mutations, Hadinnapola et al. 3 noted a severe reduction in lung diffusion capacity (Kco 33%), lower resting (SpO2 91%, 90%–94%) and exercise (SpO2 78%, 75%–82%) saturation values, and a reduced likelihood of development of pulmonary oedema in response to pulmonary vasodilator treatment. This evidence concerns the gene EIF2AK4 and pulmonary arterial hypertension.