Down Syndrome in Moderate Altitude Residents: Are There Unique Features?

Acute exposure to high altitude, which is defined as > 2500 m above sea level, is well-known to be associated with significant alterations to the cardiovascular system, with reductions in atmospheric pressure, oxygen pressure resulting in acute hypoxia, increased myocardial work, increased epinephrine release , and increased pulmonary artery pressures. 1) However, the effects of moderate altitude chronic hypoxia on the cardiovas-cular system have not been much studied. In general, clinically significant changes are difficult to demonstrate at elevations lower than 2500 m. High-altitude residents have successfully evolved adaptive regulatory mechanisms to survive in a chronic hy-poxic environment. 2) Moreover, it has been suggested that exposure to mild to moderate chronic hypoxia may induce car-dio-protective properties against various disease states such as hypertension or coronary heart disease and result in favorable outcomes. 2)3) In contrast, a few studies reported important physiological and anatomic features of pulmonary vasculature resulting in pulmonary hypertension even in healthy subjects living at moderate to high altitude. In this issue of the Journal, Espinola-Zavaleta et al. 6) report the results of their study of one-hundred twenty-seven patients with Down syndrome (DS) living in Mexico City to assess the prevalence of congenital heart disease and pulmonary hyper-tension. Mexico City is a capital of Mexico and located in the Valley of Mexico, a large valley in the high plateaus at the center of Mexico, at an altitude of 2240 m. Moderate altitude is defined as 1500–2500 m above sea level. Therefore, Halla Mountain (1950 m) in Korea is corresponding to moderate altitude but Paektu Mountain (2744 m) is at high altitude. In this study, the investigators demonstrated somewhat interesting features of DS in moderate altitude residents although this study could not provide conclusive causal relationship. First, the most prevalent congenital anomaly in DS in this study was patent ductus arteriosus, probably related with the moderate altitude of Mexico City as interpreted by the authors. Since patent ductus arteriosus closes with high oxygen tension, it is possible that a hypoxic environment and postnatal persistence of pulmonary hypertension delay closure of ductus arteriosus resulting in the high prevalence of patent ductus arteriosus in this population. Białkowski et al. 7) also reported supportive evidences of this first unique feature in this study. Larger ductal diameter and higher pulmonary artery pressure were observed in patients living at moderate to high altitudes (1500–4200 m) than in those at low altitudes (340–700 m). 7) …