Congenital diaphragmatic hernia (CDH) is a major lifethreatening cause of respiratory failure in the newborn. Although significant efforts have been undertaken to unravel the pathophysiology of CDH, our current understanding of the etiology remains spare. Here we outline recent evidence suggesting that abnormalities linked with the retinoid signaling pathway early in gestation may contribute to the etiology of CDH. These studies include 1) the effect of altering the retinoid system in vitamin A deficient and transgenic animals; 2) disruption of the retinoid system in teratogen-induced CDH in rodents, 3) the effect of co-administration of retinoids in nitrofen-induced CDH on lung and diaphragm development, and 4) clinical evidence suggesting decreased markers of vitamin A status in human CDH. Given the substantial mortality and morbidity associated with this serious developmental anomaly, advancements in this area will be critical. We feel that there is now sufficient circumstantial and direct experimental evidence to warrant further testing of the retinoid-CDH etiology hypothesis, including examination of retinoidregulated target genes that could be candidates for involvement in CDH. Severe respiratory failure in the newborn remains a main cause of neonatal death (1). Among the causes of severe respiratory failure in the newborn, congenital diaphragmatic hernia (CDH) remains the most life threatening (2, 3). Despite improvements in survival, the mortality rate is still high in many centers, and morbidity remains significant, with chronic oxygen dependence, gastroesophageal reflux, poor growth and developmental delay, and prolonged postoperative hospitalization of affected neonates (4). A major factor limiting survival in CDH is the degree of lung hypoplasia. Although tremendous efforts have been undertaken to unravel the pathophysiology of CDH, our current understanding of the pathogenesis and etiology remains spare. In this perspective, we review evidence linking abnormalities of the retinoid system and the occurrence of CDH. From the outset, it should be emphasized that a direct linkage between the etiology of CDH and retinoids has not been established. However, we summarize data from a variety of studies that provide a firm foundation for establishing the hypothesis that abnormalities within the retinoid signaling pathway during the early gestation contribute to the etiology of CDH.
CONGENITAL DIAPHRAGMATIC HERNIA: THE CLINICAL DILEMMACDH occurs in 1/2500 live births (5). This malformation was first described in 1848 by Bochdalek, and for many years was thought to be a simple hole in the diaphragm, potentially curable by surgical closure of the defect after birth. However, unlike other causes of respiratory failure in the newborn, infants with CDH do not respond to our modern therapeutic armamentarium, including exogenous surfactant, high frequency oscillatory ventilation and inhaled nitric oxide (6). When conventional therapy fails, extra-corporeal membrane oxygenation (ECMO), a highly invasive, labor-intens...