Sickle cell anemia:Ageneticblooddiseasedue to the presence of anabnormalform of hemoglobin, namelyhemoglobin S. Hemoglobin is themoleculeinred blood cells that transportsoxygenfrom thelungsto the farthest areas of the body.
Sicklecellanemia affects millions of people throughout the world. It is particularly common among people whose ancestors came fromsub-Saharan Africa; Spanish-speaking regions (South America, Cuba,CentralAmerica); Saudi Arabia; India; and Mediterranean countries, such as Turkey, Greece, and Italy. In the USA, sickle cell disease occurs in about 1 in every 500African-Americanbirths and 1 in every 1,000-1,400 Hispanic-American births.
Sickle cell anemia is caused by an error in agenethat makes the beta globin chain of hemoglobin. The resultant abnormal hemoglobin (sickle hemoglobin) deforms the red blood cells when they are under low oxygen conditions. Children who inherit 2 copies of the sickle gene, one from each parent, have sickle cell anemia. Children who inherit the sickle gene from only one parent do not have the disease, but will carry thesickle cell trait. Individuals with sickle celltraitgenerally have no symptoms. About 2 million Americans (or 1 in 12 African-Americans) carry the sickle gene.
The sicklemutationoccurred thousands of years ago. The sickle gene became common in malarious areas because it affords a selective advantage against malaria. In the U.S., Canada, and many other countries where malaria is rare today, the sickle gene can no longer use itsanti-malarial advantage. Instead, the sickle gene may be a serious threat to the carrier's children, who may inherit two abnormal sickle hemoglobingenesand have sickle cell anemia.
In sickle cell anemia, the hemoglobin molecules tend to aggregate after unloading oxygen. They form long,rod-like structures that force the red cells to assume a sickle shape. Unlike normalred cells, which are usually smooth and deformable, the sickle red cells cannot squeeze through small blood vessels.
镰状细胞块小血管剥夺the organs of blood and oxygen. This leads to the periodic episodes of pain and damages thevitalorgans. Whereas normal red blood cells last about 120 days in the bloodstream, sickle red cells die after only about 10 to 20 days. Because they cannot be replaced fast enough, the blood is chronically short of red blood cells causing anemia -- sickle cell anemia.
