Sickle Cell Anemia, Part 1 — Introduction, Incidence and Symptoms
What is sickle cell anemia?
Sickle cell anemia, or sickle cell disease, is an inherited disease that affects the production of hemoglobin (HEEM'-uh-gloh'-bin). Hemoglobin is the component of the red blood cells that carries oxygen from the oxygen-rich environment of the lungs to the relatively oxygen-poor environment of other body tissues. In sickle cell disease, the hemoglobin is abnormal. In the body's tissues, where the oxygen level is low, the abnormal hemoglobin sticks together to form clumps, which causes the normally disc-shaped red blood cells to become shaped like crescents or sickles. These malformed cells obstruct the small blood vessels (capillaries). This obstruction causes recurring painful episodes called sickle cell pain crises. The interrupted blood flow can cause tissue damage.
The abnormal hemoglobin that causes sickle cell anemia is called "hemoglobin S". As stated before, sickle cell anemia is an inherited disease, carried as an autosomal recessive trait. This means that both parents must carry the hemoglobin S gene, and each child would then have one chance in four of having sickle cell anemia.
Other conditions are grouped with sickle cell disease, including beta thalassemia and hemoglobin SC disease, which occur when hemoglobin S is inherited from one parent and another type of abnormal hemoglobin is inherited from the other parent. A person who inherits hemoglobin S from one parent and normal hemoglobin A from the other parent will have sickle cell trait. An individual with sickle cell trait or one of these other conditions usually will have no symptoms. If symptoms are present, they are likely to be very mild. Occasionally, a person with these conditions will have symptoms similar to sickle cell anemia.
The course of sickle cell anemia varies from patient to patient. The disease becomes life-threatening when damaged red blood cells break down (called a hemolytic crisis), when the spleen enlarges and traps blood cells (called a splenic sequestration crisis), or when certain infections cause the bone marrow to stop producing red blood cells (called an aplastic crisis). Some patients have repeated crises, which can damage different organs or organ systems, such as kidneys, lungs, bones, eyes, and the central nervous system. If a clot occurs in the brain, the person can suffer a stroke.
Acute painful episodes, referred to as sickle cell pain crises, are the most common complication of sickle cell disease. These crises occur when blood vessels are blocked and the organs are damaged by the reduced blood flow. The bones of the back, the long bones of legs and arms, and the chest are the areas most often affected in a pain crisis. The frequency of these crises varies considerable, from once every few years to several times each year. Each crisis will last hours to days, and may require hospitalization for treatment. Treatment generally includes measures to control pain and provide fluids, usually into a vein (intravenous or IV). Most of the disease's symptoms are caused by the physical change in the shape of the red blood cells. This is often called "sickling". The sickled cells are rigid and fragile and cannot fit through the smallest blood vessels in the body (capillaries). The misshaped red cells are then removed and destroyed by the spleen. Dehydration, infection and low oxygen levels increase the sickling of red blood cells. For these reasons, IV fluid therapy and oxygen are important parts of treatment.
Sickle cell anemia is usually diagnosed at birth by a special blood test, which is both routinely performed and legally required in all states. Additionally, sickle cell disease can now be diagnosed before birth, as early as the first trimester, by a procedure known as chronic villus sampling.
Incidence and prevalence
Sickle cell disease is much more common in certain ethnic groups. It is believed that this genetically different hemoglobin evolved as a protection against malaria, because an individual with sickle trait is more likely to survive an outbreak of malaria than someone with normal hemoglobin. Therefore, in those geographic areas where malaria is endemic, those with sickle cell trait were more likely to pass their genes on to their children. Sickle cell trait is found more commonly among people of African decent, but also Portuguese, Spanish, French Corsicans, Sardinians, Sicilians, mainland Italians, Greeks, Turks and Cypriots. Among African Americans, approximately one person out of every 500 is affected by sickle cell disease, and about 8 percent, or one person in 12, has sickle cell trait.
Symptoms vary greatly from person to person, but typical symptoms include:
- hand and foot pain
- joint and bone pain
- frequent infections
- abdominal pain
- chest pain
- shortness of breath
- rapid heart rate
- ulcers on lower legs
- delayed growth
- delayed puberty
- excessive thirst
- excessive urination
- bloody urine
- poor eyesight
- priapism (PREYE'-uh-piz-uhm), an unwanted, painful erection
Patients with sickle cell anemia may appear pale and tired, and there may be a noticeable yellowness in the eyes or skin. Crises can be induced by infection, exposure to extreme heat or cold, trauma to the body, dehydration and excessive physical exertion.
For more information
The Sickle Cell Disease Association of America, Inc.
Sickle Cell Disease Association of America, Inc.
Uriel Owens Chapter, Kansas City, Kansas
Sickle Cell Information Center
Mukta Kumar, MD
Division of Pediatric Hematology and Oncology
Department of Pediatrics
University of Kansas Medical Center
Kathy Davis, MSEd, PhD
Project Director, Connected Kansas Kids
Director, KU Kids Healing Place
University of Kansas Medical Center