Pulmonary arterial hypertension (PAH) describes a rare, progressive vascular disease caused by the obstruction of pulmonary arterioles, typically resulting in right heart failure. Whilst PAH most often manifests in adulthood, paediatric disease is considered to be a distinct entity with increased morbidity and often an unexplained resistance to current therapies. Recent genetic studies have substantially increased our understanding of PAH pathogenesis, providing opportunities for molecular

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... osis and presymptomatic genetic testing in families. However, the genetic architecture of childhood-onset PAH remains relatively poorly characterised. We sought to investigate a previously unsolved paediatric cohort (n = 18) using whole exome sequencing to improve the molecular diagnosis of childhood-onset PAH. Through a targeted investigation of 26 candidate genes, we applied a rigorous variant filtering methodology to enrich for rare, likely pathogenic variants. This analysis led to the detection of novel PAH risk alleles in five genes, including the first identification of a heterozygous ATP13A3 mutation in childhood-onset disease. In addition, we provide the first independent validation of BMP10 and PDGFD as genetic risk factors for PAH. These data provide a molecular diagnosis in 28% of paediatric cases, reflecting the increased genetic burden in childhood-onset disease and highlighting the importance of next-generation sequencing approaches to diagnostic surveillance.