Sickle Cell Disease
(Hb S Disease)
Sickle cell disease is an inherited condition characterized by sickle (crescent)-shaped red blood cells and chronic anemia caused by excessive destruction of red blood cells.
People usually have anemia and jaundice.
Worsening anemia, fever, and shortness of breath with pain in the long bones, abdomen, and chest indicate sickle cell crisis.
A special blood test called electrophoresis can be used to determine whether people have sickle cell disease.
Avoiding activities that may cause crises and treating infections and other disorders quickly can help prevent crises.
Sickle cell disease affects blacks almost exclusively. About 10% of blacks in the United States have one copy of the gene for sickle cell disease (that is, they have sickle cell trait). People who have sickle cell trait do not develop sickle cell disease, although rarely they may notice blood in their urine. About 0.3% of blacks have two copies of the gene. These people develop the disease.
In sickle cell disease, the red blood cells contain an abnormal form of hemoglobin (the protein that carries oxygen). The abnormal form of hemoglobin is called hemoglobin S. When red blood cells contain a large amount of hemoglobin S, they can become deformed into a sickle shape. Not every red blood cell is sickle-shaped. The sickle-shaped cells become more numerous when people have infections or low levels of oxygen in the blood.
The sickle cells are fragile and break apart easily. Because the sickle cells are stiff, they have difficulty traveling through the smallest blood vessels (capillaries), blocking blood flow and reducing oxygen supply to tissues in areas where capillaries are blocked. The blockage of blood flow can cause pain and, over time, cause damage to the spleen, kidneys, brain, bones, and other organs. Kidney failure and heart failure may occur.
People who have sickle cell disease always have some degree of anemia and mild jaundice. Some people have few other symptoms. Others have severe, recurring symptoms that cause enormous disability and early death. Sickle cell trait usually does not cause any problems, but rarely, people die suddenly while undergoing very strenuous exercise that causes severe dehydration, such as during military or athletic training.
Anything that reduces the amount of oxygen in the blood, such as vigorous exercise, mountain climbing, flying at high altitudes without sufficient oxygen, or an illness, may bring on a sickle cell crisis (also called an exacerbation). A sickle cell crisis may consist of a sudden worsening of anemia, pain (often in the abdomen or long bones of the arms and legs), fever, and sometimes shortness of breath. Abdominal pain may be severe, and vomiting may occur.
In children, sickle cell crisis may take the form of a chest syndrome, characterized by severe chest pain and difficulty breathing. The cause of the chest syndrome is blockage of the capillaries in the lungs. Chest syndrome can be fatal.
Most people who have sickle cell disease develop an enlarged spleen during childhood. By the time the person reaches adolescence, the spleen is often so badly injured that it shrinks and no longer functions. Because the spleen helps fight infection, people with sickle cell disease are more likely to develop pneumococcal pneumonia and other infections. Viral infections, in particular, can decrease blood cell production, so anemia becomes more severe.
The liver can become progressively larger throughout life, and gallstones often form from the pigment of broken-apart red blood cells.
The heart usually enlarges, and heart murmurs are common.
Children who have sickle cell disease often have a relatively short torso but long arms, legs, fingers, and toes. Changes in the bones and bone marrow may cause bone pain, especially in the hands and feet. Episodes of joint pain with fever may occur, and the hip joint may become so damaged that it eventually needs to be replaced.
Poor circulation to the skin may cause sores on the legs, especially at the ankles. Young men may develop persistent, often painful erections (priapism). Episodes of priapism may permanently damage the penis so that the man can no longer have erections. Blocked blood vessels may cause strokes that damage the nervous system. In older people, lung and kidney function may deteriorate.
Doctors recognize anemia, stomach and bone pain, and nausea in a young black person as signs of a sickle cell crisis. When doctors suspect sickle cell disease, they do blood tests. Sickle-shaped red blood cells and fragments of destroyed red blood cells can be seen in a blood sample examined under a microscope. Another blood test called hemoglobin electrophoresis is also done. In electrophoresis, an electrical current is used to separate the different types of hemoglobin and thus detect abnormal hemoglobin.
Further testing may be needed, depending on the specific symptoms the person experiences during the crisis. For example, if the person has difficulty breathing or a fever, a chest x-ray may be done.
Blood tests are done on relatives of people with the disorder because they also may have sickle cell disease or trait. Discovering the trait in people may be important for family planning, to determine their risk of having a child with sickle cell disease.
Newborns are routinely screened with a blood test. Newer tests can be done during early pregnancy to screen the fetus and allow prenatal counseling (see Carrier Screening) for couples who are at risk of having a child with sickle cell disease. Fetal cells obtained through amniocentesis or chorionic villus sampling are tested for the presence of the sickle cell gene.
Because sickle cell disease is rarely cured, treatment is aimed at preventing crises, controlling the anemia, and relieving symptoms. People who have this disease should try to avoid activities that reduce the amount of oxygen in their blood and should seek prompt medical attention for even minor illnesses, such as viral infections. Because people are at increased risk of infection, they should receive pneumococcal, meningococcal, and Haemophilus influenzae vaccines, and children typically take penicillin by mouth from age 4 months until age 6 years.
Drugs can help control sickle cell disease. Hydroxyurea increases the production of a form of hemoglobin found predominantly in fetuses, which decreases the number of red blood cells becoming sickle-shaped. Therefore, it reduces the frequency of sickle cell crises.
People are given folate, a vitamin that helps the body make new red blood cells.
Bone marrow or stem cells from a family member or other donor who does not have the sickle cell gene may be transplanted in a person with the disease. Although such transplantation may be curative, it is risky and so it is not often done. Recipients must take drugs that suppress the immune system for the rest of their life.
Gene therapy, a technique in which normal genes are implanted in precursor cells (cells that produce blood cells), is being studied.
Sickle cell crisis may require hospitalization. People are given fluid intravenously and drugs to relieve pain. Blood transfusions and oxygen may be given if doctors suspect that anemia is severe enough to pose a risk of stroke, heart attack, or lung damage. Conditions that may have caused the crisis, such as an infection, are treated.