Southeast Asian ovalocytosis (SAO) is a very common condition in the aboriginal peoples from Papua New Guinea, Indonesia, Malaysia, the Philippines, and southern Thailand, in areas where malaria is endemic, with prevalence varying between 5% and 25%. SAO is now known to be caused by a 27 base-pair deletion in SLC4A1, which codes for band 3, a 911 amino acid protein that is both a structural component of the red cell membrane cytoskeleton and the chloride-bicarbonate anion-exchanger in this membrane. SAO is believed to have evolved because these parts of Southeast Asia historically have had a high incidence of Plasmodium falciparum malaria, against which SAO offers clinical protection. Individuals with SAO are characterized as having oval-shaped red blood cells with increased membrane rigidity and decreased anion transport, but no clinical symptoms beyond sporadic associations with anemia in both adults and neonates. The diagnosis is made accidentally as a result of a peripheral blood smear examination, showing the characteristic rounded elliptocytes (ovalocytes).
