In two independent cohorts [11,13], rare deleterious variants in TBX4 showed significant enrichment among pediatric- compared to adult-onset IPAH cases (Columbia University Irving Medical Center, CUIMC, cohort: 10/130 vs. 0/178; PAH Biobank: 12/155 vs. 1/257, respectively). Here, TBX4 is linked to idiopathic pulmonary arterial hypertension.