Pulmonary vascular development goes awry in congenital lung abnormalities

Pulmonary vascular diseases of the newborn comprise a wide range of pathological conditions with developmental abnormalities in the pulmonary vasculature. Clinically, pulmonary arterial hypertension (PH) is characterized by persistent increased resistance of the vasculature and abnormal vascular response. The classification of PH is primarily based on clinical parameters instead of morphology and distinguishes five groups of PH. Congenital lung anomalies, such as alveolar capillary dysplasia (ACD) and PH associated with congenital diaphragmatic hernia (CDH), but also bronchopulmonary dysplasia (BPD), are classified in group three. Clearly, tight and correct regulation of pulmonary vascular development is crucial for normal lung development. Human and animal model systems have increased our knowledge and make it possible to identify and characterize affected pathways and study pivotal genes. Understanding of the normal development of the pulmonary vasculature will give new insights in the origin of the spectrum of rare diseases, such as CDH, ACD, and BPD, which render a significant clinical problem in neonatal intensive care units around the world. In this review, we describe normal pulmonary vascular development, and focus on four diseases of the newborn in which abnormal pulmonary vascular development play a critical role in morbidity and mortality. In the future perspective, we indicate the lines of research that seem to be very promising for elucidating the molecular pathways involved in the origin of congenital pulmonary vascular disease.