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South-East Asian ovalocytosis (SEAO) can be diagnosed by examination of a blood film with a high degree of reliability. These images are taken from the blood film of a 20-year-old woman, originally from the Philippines, who attended her general practitioner with non-specific symptoms. The film shows macro-ovalocytes, some of which are stomatocytic. Several cells have more than one stoma.

This condition is the result of a small deletion within the SLC4A1 gene, encoding erythrocyte band 3 (anion exchanger 1). The mutation leads to deletion of nine amino acids and rigidity of the red cell membrane. The characteristic blood film shows two populations of cells, a population of normal sized cells, which may be ovalocytic or stomatocytic, and a highly distinctive population of macro-ovalocytes. The macro-ovalocytes often have one or two stomas; the stomas may be off-center, running transversely or longitudinally and, when double, may be Y-shaped, V-shaped or parallel to each other.

SEAO heterozygosity protects against malaria and is common in parts of southern Thailand, Malaysia, Borneo, the Philippines, Brunei, Cambodia, Indonesia, and Papua and New Guinea. It also occurs in the indigenous population of the Torres Strait islands of Australia and in the Cape Coloured population of South Africa. Heterozygosity is significant only in the neonatal period, when it is associated with clinically significant hemolysis and anemia [1, 2]. Otherwise, the hemoglobin concentration and reticulocyte count are normal, hemolysis having been described only in rare families in whom one suspects an interacting disorder. The homozygous state, however, appears to be incompatible with life.

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