Abstract
A 3-year comparative study of the clinical presentation of sickle cell disease in the high and low altitudes of the Assir Province of the Kingdom of Saudi Arabia is reported. The low-lying area of the Assir Province is hot and humid, while the area at moderate altitude is cold and dry, with a reduced partial pressure of oxygen in the ambient air. Hypoxia, cold, and dehydration are recognized causes of crises in sickle cell disease. Sufferers living permanently at moderate altitude (approximately 3000 m) adapt adequately to the environmental challenges of altitude, although they are twice as likely as their valley counterparts to present with ill-health. The presence of the B-thalassemia gene appears to decrease the frequency of occurrence of symptoms among sufferers in both mountain and valley locations, and may contribute to the survival of the sufferer living permanently at moderate altitude.