Science Dictionary
sickle cell anemia   (sĭk'əl)  Pronunciation Key 
A hereditary disease characterized by red blood cells that are sickle-shaped instead of round because of an abnormality in their hemoglobin, the protein that carries oxygen in the blood. Because of their shape, the cells can cause blockage of small blood vessels in the organs and bones, reducing the amount of available oxygen.

Our Living Language  : Sickle cell anemia is a genetic mutation that can be either detrimental or beneficial depending on the number of copies of the mutated gene a person inherits. While it is harmful if a person inherits two copies of the mutated gene (one from each parent), a person could actually benefit if only one copy of the gene is inherited. The defective gene causes red blood cells to be distorted into a sickle shape, which makes it hard for them to pass through the tiny blood vessels where they give oxygen to body tissues. Inheriting two copies of the mutated gene results in a lifelong disease that causes anemia, pain, and other complications. With just one copy of the gene, though, only mild sickling occurs, and the disease does not manifest itself. This mild sickling, however, is also harmful to the parasites that cause malaria and can protect a person from that disease. In a region like tropical Africa where malaria is common, people who have the mutation in one gene are more likely to ward off a malaria infection and to live long enough to have children, who then inherit the gene. And because a person is less likely to inherit two copies of the gene instead of just one, the benefits of the gene outweigh its risks for most people in these regions. About one in 500 African-American newborns and one out of every 1,000 to 1,400 Hispanic babies are diagnosed with sickle cell anemia each year in the United States. Almost ten percent of African Americans carry the sickle cell gene. There is no cure for the disease, but treatment can reduce pain and prolong life.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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