(Left) Micro Discovery/Corbis; (right) NASA

The disease that destroys red blood cells by causing them to take on a rigid crescent, or “sickle,” shape rather than a normal disc shape is called sickle cell anemia. The disease is hereditary, or passed down from parents to their offspring. Sickle cell anemia occurs mainly in people of African descent but can also be found in persons of the Middle East, the Mediterranean, and India.

Sickle cell anemia is caused by an abnormal type of hemoglobin, called hemoglobin S. Hemoglobin is the protein in red blood cells that carries oxygen to the tissues of the body. When the red blood cells release their oxygen to the tissues, hemoglobin S becomes stacked and twisted into rods. These rods cluster into bundles that distort and elongate the cells, causing them to become rigid and assume a sickle shape. This phenomenon is to some extent reversible after the cells become oxygenated once more. Repeated sickling, however, ultimately results in irreversible distortion of the red cells. The sickle-shaped cells become clogged in small blood vessels, obstructing circulation and eventually damaging and destroying various tissues.

In order to get sickle cell anemia, the hemoglobin S gene must be inherited from both parents. A person who inherits the sickle cell gene from one parent and a normal hemoglobin gene from the other parent is a carrier of the sickle cell trait. Most people with the sickle cell trait have no symptoms of disease. The overall mortality rate of persons with the sickle cell trait is no different from that of a normal comparable population.

An estimated 1 in 12 blacks worldwide carries the sickle cell trait, while about 1 in 400 has sickle cell anemia. If both parents have the sickle cell trait, the chances are 1 in 4 that a child born to them will develop sickle cell anemia. Through the analysis of amniotic fluid surrounding a fetus (a process called amniocentesis), a testing procedure done in the early stages of pregnancy, it is possible to detect sickle cell anemia in the fetus.

Sickle cell anemia produces many of the symptoms of chronic anemia (an ongoing condition in which the body either does not have enough red blood cells or they are lacking in hemoglobin). These symptoms include fatigue, pale skin, and shortness of breath. Other symptoms are possible, such as the susceptibility to infection, jaundice and other eye problems, delayed growth, and bouts of severe pain in the abdomen, bones, or muscles.

There is no cure for sickle cell anemia; most care is devoted to alleviating symptoms. Infants and young children with the disease are given regular daily doses of penicillin, an antibiotic, to prevent serious infection. In some cases blood transfusions are given regularly to prevent organ damage and stroke and to relieve the worst symptoms of red blood cell loss. In severe cases bone marrow transplants have been of some benefit. Some drugs reduce the principal symptoms of the disease.