KCNK3 and idiopathic pulmonary arterial hypertension: Monoallelic heritable variants in BMPR2, TBX4, ABCC8 and GDF2 likely cause 2%–6% of HPAH/IPAH in children, while variants in KCNK3, ACVRL1, ENG and SMAD9 are rare causes of cPAH.9 Biallelic variants in GDF2 and KCNK3 have been identified in very early-onset, severe cPAH in at least two families.11 12 Herein, we identified biallelic variants in ATP13A3 as the genetic cause of cPAH in three families including five affected children presenting under 3 years of age.