Since overexpression of BMP-4 in endothelial cells enhances vascular remodeling in pulmonary hypertension (57) it cannot be excluded that higher serum levels of BMP-4 can contribute to the vascular abnormalities frequently observed in the C group (e.g., telangiectasia, PAH and arterial hypertension). Here, BMP4 is linked to pulmonary arterial hypertension.