NOTCH3 and idiopathic pulmonary arterial hypertension: Mean serum NOTCH3-ECD levels were significantly higher for patients with IPAH (mean ± s.d., 19.9 ± 5.5 ng ml−1) compared to individuals without PH (10.5 ± 1.9 ng ml−1; P < 0.001) (Fig. 1a).