Sickle cell anemia / malaria connection

Sickle cell anemia is a genetic blood disorder that occurs when production of red blood cells contain abnormally shaped hemoglobin that, in effect, also distort red blood cells making them look crescent-shaped or “sickle-like” (1). The hemolytic condition occurs because these cells have a lifespan of about 20 days versus the normal cell lifespan of 120 days; the marrow and spleen clear them out early leading to a low count in total red blood cells (1). Bone marrow is not able to replace the red blood cells fast enough (2).

About .2% of blacks of African origin are affected by sickle cell anemia as well as other groups (1). It affects millions worldwide and afflicts them with long-term pain and fatigue (2). Improved care is helping to keep patients alive into 40s and 50s (2). No cure is known, but bone marrow transplants are offering promising results (2).

The sickle cell trait is benign, passed by a defective gene (1). Two defective genes cause the blood disorder (1). Sickle cell genes are thought to have evolved as recently as 40,000 years ago as a defense against malaria in African populations (3). This hypothesis, tested in mice, is thought to be correct because of the anemia encourages rapid elimination of infected red blood cells by the liver and spleen, which may have led to increased survival against malaria (4-6).

References

1. Nowak TJ, Handford AG. Pathophysiology: Concepts and Applications for Health Professionals. New York: McGraw-Hill, 2004.
2. National Heart and Lung Institute. Sickle cell anemia. "What is sickle cell anemia?" Available at: http://www.nhlbi.nih.gov/health/dci/Diseases/Sca/SCA_WhatIs.html.
3. Boaz N. Evolving Health: The Origins of Illness and How the Modern World is Making us Sick. New York: John Wiley & Sons, 2009.
4. Min-Oo G, Fortin A, Tam MF, Gros P, Stevenson MM. Phenotypic expression of pyruvate kinase deficiency and protection against malaria in a mouse model. Genes Immun 2004;5:168-75.
5. Min-Oo G, Tam M, Stevenson MM, Gros P. Pyruvate kinase deficiency: correlation between enzyme activity, extent of hemolytic anemia and protection against malaria in independent mouse mutants. Blood Cells Mol Dis 2007;39:63-9.
6. Durand PM, Coetzer TL. Pyruvate kinase deficiency protects against malaria in humans. Haematologica 2008;93:939-40.