NOTCH3 and idiopathic pulmonary arterial hypertension: The mean serum NOTCH3-ECD levels were also similar between individuals without PH in the San Diego, Phoenix and Boston cohorts (mean ± s.d., 10.6 ± 1.4 ng ml−1, 10.2 ± 2.2 ng ml−1 and 10.9 ± 1.4 ng ml−1, respectively; P = 0.70), with a statistically significant difference in serum NOTCH3-ECD levels between individuals with IPAH and individuals without PH in each cohort (P < 0.001) (Fig. 1b).