Southeast Asian ovalocytosis

Southeast Asian ovalocytosis is an inherited blood disorder in which red blood cells are oval rather than round. It resembles hereditary elliptocytosis but is a distinct condition. The primary defect lies in the gene for the red cell anion transporter known as band three, a protein in the membrane itself rather than in the cytoskeleton, and in affected cells band three binds ankyrin more strongly than normal. The cells become more rigid and more resistant to osmotic and temperature stress, and this is thought to explain a marked resistance to infection by the malaria parasite Plasmodium falciparum, which relies on that protein to enter red cells. The condition is common in some communities in Malaysia and Papua New Guinea, and an incidence of about 35 percent on the north coast of Madang Province in Papua New Guinea, where malaria is endemic, is cited as an example of natural selection.