ovalocytosis

Ovalocytosis is a red blood cell morphologic abnormality in which a significant proportion of circulating erythrocytes appear oval on a peripheral blood smear. It is usually a hereditary condition and is most commonly recognized in the form known as Southeast Asian ovalocytosis (SAO).

SAO arises from a genetic alteration of red blood cell membrane proteins, most notably in the SLC4A1 gene encoding the band 3 anion exchanger. The mutation disrupts membrane stability and yields rigid, oval-shaped erythrocytes with reduced deformability. The trait is relatively common in certain populations, particularly in Melanesia and parts of Southeast Asia, including areas around Papua New Guinea.

Clinical presentation varies. Many individuals are asymptomatic, while others may have mild chronic hemolysis, compensated anemia, or splenomegaly. The rigidity of the ovalocytes can confer some protection against Plasmodium falciparum malaria in endemic regions. Laboratory findings may include mild reticulocytosis or indirect signs of hemolysis, but routine blood tests can be otherwise normal. The hallmark is the characteristic oval appearance of red cells on a smear; some cells may be stomatocytic or display pleomorphic shapes.

Diagnosis is based on peripheral blood smear findings and is supported by genetic testing for SLC4A1 mutations. Differential diagnosis includes other elliptocytoses and stomatocytoses, though those conditions differ in cell shape and membrane properties.

Management is typically observation; treatment is reserved for any symptoms related to anemia or other complications. The prognosis for heterozygous individuals is generally good, and most people lead normal lives.