NOTCH3 and idiopathic pulmonary arterial hypertension: In three geographically distinct cohorts comprising 341 individuals with IPAH (267 women, 74 men) and 376 healthy individuals (278 women, 98 men), serum NOTCH3-ECD levels were significantly higher in individuals with IPAH (mean ± s.d.: 19.9 ± 5.5 ng ml−1) compared to controls (10.5 ± 1.9 ng ml−1; P < 0.001), with consistent results among the three cohorts.