NTRK1 and pulmonary arterial hypertension: One study65 used an immunoassay platform to measure 28 proteins associated with receptor tyrosine kinase signalling in 152 patients with different presentations of pulmonary hypertension; PAH, chronic thromboembolic disease, pulmonary hypertension due to diastolic heart failure (preserved ejection fraction), pulmonary hypertension due to systolic heart failure (reduced ejection fraction) and heart failure without pulmonary hypertension, as well as healthy control subjects.