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SICKLE CELL DISEASE: THE BASICS

Sickle cell disease is an inherited condition that is most common among people whose ancestors come from Africa, the Middle East, the Mediterranean basin, and India.

In West Africa various ethnic groups gave the condtion different names:

Ga tribe: chwechweechwe

Faute tribe: nwiiwii

Ewe tribe: nuidudui

Twi tribe: ahotutuo

In the western literature, the first description of sickle cell disease was by a Chicago physician, James B. Herrick, who noted in 1910 that a patient of his from the West Indies had an anemia characterized by unusual red cells that were "sickle shaped."

In the U.S., it affects primarily African Americans, about 0.3% of whom have some form of sickle cell disease, and approximately 10% of whom carry the sickle cell trait. There are approximately 80,000 individuals in the United States with sickle cell disease.

The red blood cells of people with sickle cell disease contain an abnormal type of hemoglobin, the oxygen-carrying pigment, called hemoglobin S. The deficiency of oxygen in the blood causes hemoglobin S to crystallize, distorting the red blood cells into a sickle (or crescent) shape, making them fragile and easily destroyed, leading to anemia.

The "sickled" blood cells then are unable to squeeze through the smaller blood vessels (arterioles and capillaries). When the tissues are deprived of an adequate blood supply, painful symptoms occur. Complications can include stroke, bone pain, kidney damage and breathing problems. The recurrent pain caused by the disease can interfere with many aspects of the patients' lives including education, employment, and psychosocial development.

Normal Hemoglobin and Sickle Hemoglobin

While sickle hemoglobin and normal hemoglobin carry the same amount of oxygen, two major differences exist between the two kinds of cells. First, they differ in the way they flow through the blood vessels. Normal hemoglobin is found in disc-shaped red blood cells that are soft (like a bag of jelly), which enables them to easily flow through small blood vessels. Diseased red blood cells which are sickle-shaped and are hard (like pieces of wood), often get stuck in small blood vessels and stop the flow of blood.

The second difference between the two types of cells is their longevity. Sickle cells do not live as long as normal cells. Normal, healthy cells can survive for about 120 days, while the more fragile sickle cells can survive for about 60 days or less. Unfortunately, the body cannot make new red blood cells as fast as it loses sickle blood cells. As a result, a sickle cell patient has fewer red blood cells and less hemoglobin than normal red blood cells. This decreased hemoglobin (called anemia), in turn, results in less oxygen being available for use by the cells of the body.

How Do You Get Sickle Cell Disease?

The only way you can get sickle cell disease is by genetic inheritance. You cannot get sickle cell disease by contact or by blood transfusions.

There are many forms of sickle cell disease. These occur whenever the gene for abnormal hemoglobin S combines with any other gene for abnormal hemoglobin, (e.g., C, O, E, Beta-Thalassemia, etc.). The resulting types of sickle cell disease in the above examples would be SC, SO SE, and S Beta-Thalassemia, respectively. However, when one hemoglobin S gene combines with a second hemoglobin S gene, the result is a particular type of sickle cell disease known as sickle cell anemia, or SS disease. This is probably the most well known form of sickle cell. Even though we often see the term sickle cell anemia used to refer to all types of sickle cell disease, technically, SS disease is the only form of sickle cell disease that is correctly referred to as sickle cell anemia. The umbrella term, "sickle cell disease" does, however, refer to any of the above conditions.

As sickle cell is a genetic disorder, in order to have sickle cell disease, you must inherit a hemoglobin S gene. Inheriting the hemoglobin S gene from only one parent and a normal hemoglobin gene from the other parent means you only have the trait, and not the disease. Anyone who has the trait has the potential for passing it on to his or her child.

Sickle Cell Disease and Sickle Cell Trait

People who have inherited a hemoglobin S gene from one parent and a second abnormal hemoglobin gene from the other parent manifest symptoms of sickle cell disease by having sickled cells in the bloodstream. People with sickle cell trait usually do not manifest any of the problems associated with sickle cell disease. However, there have been cases that show people with sickle cell trait can exhibit sickle cells under extreme conditions of physical stress or low atmospheric oxygen.

More of What Happens When You Have Sickle Cell Disease

Clogged blood capillaries can lead to different types of problems, depending upon where the blockage occurs. The outcome of this blockage may lead to problems such as kidney infections; intense pain in the chest, arms and legs; death and decay of tissues, especially in the joints; disease of the retina of the eye; slow healing sores or ulcers; gallstones; and cerebral vascular accidents, or "strokes." The health problem known as anemia may result because the sickle cell does not last as long as the normal red blood cell. Normal red blood cells last 120 days; sickle cells last, at the most, 60 days. This shorter lifespan means fewer circulating red blood cells and, therefore, a smaller amount of hemoglobin at any given time compared to normal. Low hemoglobin (anemia) is manifested as fatigue and weakness.

Is There a Cure?

Presently, there is no cure for sickle cell disease. However, there is treatment for the pain and other aspects of the disease. Pain medication, antibiotics, rest, good nutrition, supplementation with folic acid and high fluid intake are all helpful treatments for aspects of sickle cell disease. At times, invasive procedures such as blood transfusions and surgery may be needed. Recently, treatment with hydroxyurea has been shown to increase the production of fetal hemoglobin, which does not sickle like normal sickle cells. Other experimental drugs are currently being used in clinical trials with promising results. Bone marrow transplantation has proven to be a cure in a very limited number of cases, yet only a few people are eligible for this extremely risky procedure (which, if successful, requires a lifetime of post-surgical maintenance with anti-rejection drugs). Many people are also exploring alternative types of treatments such as bio-feedback, acupuncture, herbal medicine, and meditation.

How Do You Know If You Have Sickle Cell Trait?

The easiest way to find out if you have the trait is to be tested by a simple blood test. This test is available in several hospitals, clinics, and in some university health centers. If you and your partner test positive for hemoglobin S or another abnormal form of hemoglobin, and you wish to become pregnant, it is imperative that you have genetic counseling to determine your risks for having a child with sickle cell disease.

Tips for People in High Risk Groups

For those population groups known to be susceptible to sickle cell disease, it is recommended that they read or strive to know more about the disease manifestation. Genetic counseling and screening for preventive measures is highly recommended. Also, information on genetic transmission of the disease is highly advisable before making reproductive decisions. For those who have been identified as having sickle cell disease, they should be aware of situations that can lead to crisis. These situations include bacterial infections, stressful environments at home and in the workplace, dehydration, sudden temperature variations, and overexertion.

Adapted from material produced by the NIH