Sickle cell disease is a general term for a group of related genetic disorders caused by sickle hemoglobin (Hgb S). In many forms of the disease, the red blood cells change shape upon deoxygenation because of polymerization of the abnormal sickle hemoglobin. This process damages the red blood cell membrane, and can cause the cells to become stuck in blood vessels. This deprives the downstream tissues of oxygen and causes ischemia and infarction. The disease is chronic and lifelong. Individuals are most often well, but their lives are punctuated by periodic painful attacks. In addition to periodic pain, there may be damage of internal organs, such as stroke. Lifespan is often shortenend. It is common in people from parts of the world where malaria is or was common, especially in West Africa or in descendents of those peoples. Sickle cell disease can occur in any individual of any color or ethnicity, however.

"Sickle cell anemia" is the name of a specific form of sickle cell disease in which there is homozygosity for the mutation that causes Hgb S. Other forms of sickle cell disease include sickle-hemglobin C disease, sickle beta-plus-thalassemia, and sickle beta-zero-thalassemia. Unlike sickle cell anemia, these other forms of sickle cell disease are compound heterozygous states in which the individual has only one copy of the mutation that causes Hgb S and one copy of another abnormal hemoglobin gene. It is important to know that "sickle cell anemia" is the proper name of a specific type of "sickle cell disease", and that "sickle cell disease" is a non-specific term. Because the different forms of sickle cell disease are quite different, one must be sure to specify the exact form of the disease in question.

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Sickle cell anemia occurs, almost, exclusively in blacks.

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