What Is Southeast Asian Ovalocytosis?
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Southeast Asian Ovalocytosis - A Red Blood Cell Disorder

Published on May 24, 2023 and last reviewed on Aug 28, 2023   -  5 min read


There is a common hereditary red blood cell condition called Southeast Asian ovalocytosis that is prevalent in Southeast Asia.


A genetic red blood cell condition called Southeast Asian ovalocytosis is common in several ethnic groups in Malaysia, Papua New Guinea, the Philippines, and Indonesia. The rigidity and diminished expression of numerous erythrocyte antigens are characteristics of ovalocyte erythrocytes. Plasmodium knowlesi and other malarial strains, including Plasmodium falciparum, are unable to invade the ovalocytes in vitro.

Oval-shaped red blood cells, which are resistant to invasion by the malaria parasite Plasmodium falciparum, are what give it its distinctive appearance. While having ovalocytosis reduces the risk of getting malaria, it can also cause other health issues, including hemolytic anemia and splenomegaly. Although the disease is mostly asymptomatic, it has been linked to modest hemolysis symptoms such as intermittent jaundice and gallstones.

What Is the Epidemiology of Southeast Asian Ovalocytosis (SAO)?

The genetic disorder Southeast Asian ovalocytosis (SAO) is most prevalent in the native populations of Malaysia, Indonesia, Papua New Guinea, and the Philippines in Southeast Asia. Between 10 to 50 percent of various groups in the area are carriers of the SAO gene, a large range.

The Orang Asli tribes in Malaysia have the greatest carrier frequencies, with certain villages having a carrier frequency of up to 90 percent. In Indonesia, the Dayak and Toraja tribes in Kalimantan and Sulawesi, respectively, have the greatest frequencies. The Melanesian population in Papua New Guinea has a high carrier frequency of up to 70 percent.

A person with one copy of the mutant gene will have the ovalocytic phenotype because SAO is inherited in an autosomal dominant way. The prevalence of SAO is significantly influenced by the carrier frequency of the SAO gene in a population since carriers can convey the mutant gene to their progeny even if they do not personally display the ovalocytic phenotype.

In general, the epidemiology of SAO emphasizes how crucial it is to comprehend the genetic and environmental variables that influence the incidence of hereditary disorders in various populations.

What Are the Genetics of SAO?

Since SAO is inherited autosomal dominant, a heterozygote will have the ovalocytic phenotype. Homozygous individuals typically die in infancy from severe hemolytic anemia. The chromosome 17q21-qter has the defective gene that causes SAO, which produces the membrane protein band 3 or anion exchanger 1 (AE1).

What Is the Pathophysiology of SAO?

Because of their distinctive form, the ovalocytes' red blood cells in SAO are defended against invasion by the malaria parasite. The red blood cell membrane's shape and flexibility are preserved by the membrane protein AE1, which is mutated in SAO. When there is less protein on the cell surface as a result of the AE1 mutation in SAO, the membrane's flexibility is reduced and the cell shape becomes more rigid.

What Are the Clinical Manifestations of SAO?

The majority of people with Southeast Asian ovalocytosis (SAO) are asymptomatic and have no health issues. Nonetheless, some people with SAO may experience clinical symptoms such as:

  • Hemolytic Anemia: SAO can result in hemolytic anemia, a disease where red blood cells are being lost more quickly than they are being made. This may result in symptoms including weakness, pallor, jaundice, exhaustion, and shortness of breath.

  • Splenomegaly: As more red blood cells are being destroyed, some people with SAO may experience splenomegaly, which is an enlargement of the spleen. Abdominal discomfort, early satiety, and a sense of fullness can all be symptoms of splenomegaly.

  • Gallstones: These are hard deposits that occur in the gallbladder or bile ducts, and SAO can make them more likely to form. Jaundice, nausea, vomiting, and stomach discomfort are all symptoms of gallstones.

  • Pseudohyperkalemia: SAO can result in pseudohyperkalemia, a condition where the blood's potassium levels seem to be raised as a result of potassium being released from red blood cells during blood sampling. As pseudohyperkalemia typically has no symptoms, no therapy is necessary.

  • Exercise-Induced Hematuria: Some SAO sufferers may develop exercise-induced hematuria, which is the development of blood in the urine following physical activity. Hematuria brought on by exercise is typically harmless and does not need to be treated.

It is crucial to remember that not everyone with SAO develops these clinical indications, and symptom intensity can vary greatly between people.

How Is SAO Diagnosed?

A blood test that detects ovalocytes in red blood cells is typically used to diagnose Southeast Asian ovalocytosis (SAO). To identify SAO, the following tests are done-

  • Peripheral Blood Smear: It is a lab test in which a drop of blood is studied under a microscope. Red blood cells in individuals with SAO are oval-shaped rather than the typical biconcave disc form.

  • Osmotic Fragility Test: Performed in a lab, assesses how well red blood cells can survive variations in the salt content of solutions. Red blood cells in people with SAO are more resistant to lysis than red blood cells in healthy people.

  • Acidified Glycerol Lysis Test: This laboratory test assesses how well red blood cells can resist being exposed to an acidified glycerol solution. Red blood cells in people with SAO are more resistant to lysis than red blood cells in healthy people.

  • Genetic Testing: Genetic testing can reveal whether the SAO gene mutation is present. When someone has a family history of SAO, this test is typically performed to confirm the diagnosis.

What Is the Treatment for SAO?

The majority of people with Southeast Asian ovalocytosis (SAO) have no symptoms and do not need any special care. Nonetheless, therapy options for those who develop clinical SAO signs include the following:

  • Supplementing With Folic Acid: In people with SAO, folic acid promotes the synthesis of red blood cells and helps avoid anemia.

  • Blood Transfusions: Blood transfusions may be required to restore destroyed red blood cells in those with severe anemia or consequences such as gallstones or splenomegaly.

  • Splenectomy: The surgical removal of the spleen may be required in patients with significant problems such as recurring gallstones or splenomegaly in order to relieve symptoms.

  • Treatment of Exercise-Induced Hematuria: In people with SAO, exercise-induced hematuria is mostly benign and does not need to be treated. However, reducing vigorous activity may be helpful in people with recurrent hematuria.

  • Treatment of Pseudohyperkalemia: In people with SAO, pseudohyperkalemia is typically asymptomatic and does not need to be administered. Those with high potassium levels on repeated blood tests, however, can benefit from blood sampling using a different technique or from using supplements that stop potassium from leaking out of red blood cells.


A mutation in the AE1 gene results in SAO, a prevalent red blood cell condition in Southeast Asia. While people with SAO are mostly asymptomatic, some people can experience splenomegaly and hemolytic anemia. Ovalocytosis is present in SAO, which offers some malaria protection but also causes a lot of health issues. Treatment is often supportive when a peripheral blood smear is examined to make the diagnosis.

Last reviewed at:
28 Aug 2023  -  5 min read




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