n HOW DOES SICKLE CELL DISEASE AFFECT THE BLOOD? Red blood cells normally contain hemoglobin A, also called adult hemoglobin. A child who has sickle cell disease has inherited an abnormal gene (called a gene mutation) for the production of hemoglobin. This gene mutation causes the body to make hemoglobin S, or sickle hemoglobin, instead of hemoglobin A. Sickle hemoglobin is not efficient at carrying oxygen. Under certain stressful conditions, such as fever and dehydration, the red blood cells change into a rigid sickle shape, like a crescent moon. When this happens, the sickle-shaped cells stick to each other and to the blood vessel walls instead of flowing easily through the vessels like soft, round, normal blood cells. When these sickle-shaped cells stick together, they block the flow of blood through the vessel and prevent the tissues from getting fresh, oxygenated blood. This is what causes pain, the most well-known symptom of sickle cell disease. However, this lack of oxygen also is responsible for many other problems, which will be addressed later. People who do not have sickle cell disease make red blood cells that contain hemoglobin A. These red blood cells can live for almost 120 days. People with sickle cell disease make red blood cells that contain hemoglobin S. These red blood cells can sickle and on average live for only 10–20 days before breaking apart. This breaking apart of red blood cells is called hemolysis . It is hard for the body to replace the red blood cells fast enough, which causes anemia, a low hemoglobin level in people living with sickle cell disease. Anemia is the medical term for a low hemoglobin level. Anemia causes people to feel tired and weak, and severe anemia may require a blood transfusion.
n WHO GETS SICKLE CELL DISEASE? Sickle cell disease is a genetic disorder, meaning that a child can inherit the disease from parents who carry the gene mutation for sickle cell disease. Many people associate sickle cell disease with Africans and people of African descent. Although it is extremely common in Africa, sickle cell disease actually began in four areas of the world with a high incidence of malaria: Africa, India, the Mediterranean, and the Middle East. It is believed that the sickle cell mutation developed as a way to protect people living in these areas from malaria. (Malaria is a blood disease transmitted to humans by certain mosquitoes.) Today, there are people with sickle cell disease living in almost every country.
n HOW IS SICKLE CELL DISEASE INHERITED? Sickle cell disease is inherited in the same way that many of our genetic traits are inherited from our parents. Sickle cell disease is a recessive condition that occurs when a child inherits the sickle cell gene from both parents, one from the mother and one from the father. If a child only
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