In: Disease1 Jun 2010
An abnormal type of hemoglobin— hemoglobin S—causes sickle cell anemia. In tropical regions of the world where malaria is prevalent, individuals with a single copy of this particular genetic mutation have a survival advantage. In areas where malaria is prevalent, inheriting one copy of the mutation is beneficial because it aids in combating the disease. Inheriting two copies of the mutation, however, portends tragedy (Figure 1). People from these regions migrated over time, married one another, and had children, and some of these children inherited two copies of the mutation.
Figure 1 Inheritance of sickle cell anemia. (With permission from White A. Black health care.
Normal hemoglobin consists of two alpha and two beta chains to form a four-chain tetramer (Figure 2). In sickle cell anemia, valine is substituted for glutamic acid in both beta chains (hemoglobin SS). This substitution alters the beta chain and its interaction with other beta chains. The altered beta chains bind with other beta chains in deoxygenated red blood cells (RBCs). Polymerization occurs, and hemoglobin polymers distort the RBCs into sickled shapes; these changes ultimately cause vaso-occlusion (Figure 3). Polymerization leads to abnormal permeability, red blood cell dehydration, endothelial adhesion, and irreversible sickling. The lack of blood flow results in anemia, pain crises, and, eventually, infarction.
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Figure 2 Structure of the hemoglobin molecule. (From Lonergan GJ, Cline DB, Abbondazo SL. Sickle cell anemia. Armed Forces Institute of Pathology Archives. RadioGraphics 2001;21:971-994. © Radiological Society of North America.
Individuals who inherit hemoglobin S from one parent and normal hemoglobin (hemoglobin A) from the other parent will have sickle cell trait, which usually causes only mild symptoms or none at all. Most people do not even know that can be interrupted in any major organ, they have the trait until they are tested. In patients with sickle cell anemia, the hemoglobin molecules stick together in long, rigid rods after they release oxygen. These rods cause the RBCs to become hard and sickle-shaped, making them unable to squeeze through tiny blood vessels. The misshapen cells can become stuck in the small blood vessels, causing a blockage that deprives the body’s cells and tissues of blood and oxygen (Figure 4).
Figure 3 Pathology of sickle cell anemia. The distorted shapes of red blood cells eventually cause vaso-occlusion. From Lonergan GJ, Cline DB, Abbondazo SL. Sickle cell anemia. Armed Forces Institute of Pathology Archives. RadioGraphics 2001; 21:971-994. © Radiological Society of North America.
Duane A. Bonds, MD, leader of the sickle cell disease scientific research group at the National Heart, Lung, and Blood Institute (NHLBI), states that when the misshapen cells get stuck in the small blood vessels, “it’s like having mini heart attacks throughout the entire body.” online pharmacy uk
Figure 4 Blockage of small blood vessels resulting from misshapen red blood cells. (From Delta Health Education partnership.
causing severe pain and organ damage where the flow has been blocked. Individuals who experience painful crises may complain of bone pain, difficulty in breathing, fever, and extreme fatigue. Recognizing that sickled cells are abnormal, the body destroys them at a faster rate than it can replenish them, causing anemia and predisposing these patients to infections.
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