sickle cell disease
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sickle cell diseaseor
sickle cell anemia,inherited disorder of the blood in which the oxygen-carrying hemoglobinhemoglobin
, respiratory protein found in the red blood cells (erythrocytes) of all vertebrates and some invertebrates. A hemoglobin molecule is composed of a protein group, known as globin, and four heme groups, each associated with an iron atom.
..... Click the link for more information. pigment in erythrocytes (red blood cells) is abnormal. This "hemoglobin-S" crystallizes in small capillaries, where the concentration of oxygen in the blood is low (but sufficient for normal hemoglobin), causing the red blood cells to assume distorted, sicklelike shapes. Linus PaulingPauling, Linus Carl
, 1901–94, American chemist, b. Portland, Oreg. He was one of the few recipients of two Nobel Prizes, winning the chemistry award in 1954 and the peace prize in 1962.
..... Click the link for more information. discovered the chemical abnormality of the hemoglobin molecule that causes the erythrocyte sickling in 1949.
The sickled red blood cells tend to clog small blood vessels, depriving the tissues they serve of blood and oxygen. Painful "crises" result, with symptoms depending on the site affected (e.g., joint and abdominal pain or kidney damage). Strokes or seizures can occur if the brain is affected. Lung infections resulting from the patient's disinclination to take painful deep breaths are a frequent complication. In addition, the sickled erythrocytes are fragile and subject to rupture and destruction, leading to hemolytic anemia (reduction of oxygen-carrying hemoglobin caused by premature destruction of red blood cells) and such symptoms as fatigue, jaundice, and headaches.
There is no cure for the disease, but advancements in treatment have improved median survival to 42 years for men and 48 years for women. Cerebral hemorrhage or shock is the usual cause of mortality in children. Recent studies have indicated that regular blood transfusions can prevent strokes in children. Anemia is treated with folic acid. Sickle cell crises may be treated with intravenous hydration, pain medication, antibiotics, oxygen, and transfusions. Hydroxyurea, formerly used as a cancer treatment, has been helpful to many adults with the disease, lessening the frequency and severity of crises. New drugs for reducing the severity of crises are being tested as well. One acts as a lubricant, allowing sickled cells to flow more easily through tiny vessels. The other helps to prevent tissue deprived of blood from dying during a crisis.
The disease occurs mainly in persons of sub-Saharan African, especially W African, origin, but it also occurs in persons of Mediterranean, Middle Eastern, and Indian origin. The mutation may at one time have had an advantageous effect; those who have the sickle cell trait have a higher survival rate in malaria-infested zones.
Under normal circumstances the disease occurs only in those patients who inherit the gene for the abnormal hemoglobin from both parents. This so-called homozygous form of the disease occurs in 1 in 400 African Americans. About 8% of African Americans have sickle cell trait; that is, they are heterozygotes, usually symptomless carriers who have inherited a normal hemoglobin gene from one parent and hemoglobin-S from the other. There are also intermediate forms of the disease that result when a gene for hemoglobin-S is inherited from one parent and a gene for any of several other abnormal kinds of hemoglobin is inherited from the other. Genetic screening (see genetic testinggenetic testing,
medical screening for genetic disorders, by examining either a person's DNA directly or a person's biochemistry or chromosomes for indirect evidence. Testing may be done to identify a genetic disorder a person has, whether the disorder is already evident or not,
..... Click the link for more information. ) is recommended for prospective parents at risk of passing on the disease. If both parents are carriers (i.e., have sickle cell trait), then each child has a one in four chance of having sickle cell disease.