South East Asian Ovalocytosis (SAO), is an inherited erythrocyte defect caused by a mutation in the SLC4A1 gene. This gene codes for the membrane protein band 3, one of the proteins that gives the erythrocyte its shape. Red blood cells exhibit a characteristic oval to elliptical shape with thickened and rigid membranes, making them less malleable. Although most carriers are asymptomatic, SAE may be accompanied by mild hemolysis or anemia in rare cases.

Microscopically, knizocytes, ovalocytes and stomatocytes are seen. The stomatocytes may show a V or Y shape in addition to the classic slit shape.