What is sickle cell disease?
Sickle cell disease is an inherited disease of red blood cells. It is characterized by pain episodes, anemia (shortage of red blood cells), serious infections and damage to vital organs.
The symptoms of sickle cell disease are caused by abnormal hemoglobin. Hemoglobin, the main protein inside red blood cells, carries oxygen from the lungs and takes it to every part of the body. Normally, red blood cells are round and flexible and flow easily through blood vessels. But in sickle cell disease, the abnormal hemoglobin causes red blood cells to become stiff and, under the microscope, may look like a C-shaped farm tool called a sickle. These stiffer red blood cells can get stuck in tiny blood vessels, cutting off the blood supply to nearby tissues. This is what causes pain (called a sickle cell pain episode or crisis) and sometimes organ damage in sickle cell disease. Sickle-shaped red blood cells also die and break down more quickly than normal red blood cells, resulting in anemia.
There are several common forms of sickle cell disease. These are called SS (individuals inherit one sickle cell gene from each parent); SC (the child inherits one sickle cell gene and one gene for another abnormal type of hemoglobin called “C”); and S-beta thalassemia (the child inherits one sickle cell gene and one gene for beta thalassemia, another inherited anemia).
What medical problems occur with sickle cell disease?
The effects of sickle cell disease vary greatly from one person to the next. Some affected children and adults are usually healthy, while others are frequently hospitalized. Some common problems seen in sickle cell disease include the following:
Infections. Infants and young children with sickle cell disease are especially vulnerable to serious bacterial infections, such as those that cause meningitis (infection of the lining of the brain) and blood infection. Infections are a major cause of death in children with sickle cell disease. But deaths have declined dramatically since doctors began routinely treating children with sickle cell disease with the antibiotic penicillin to help prevent these infections. Affected children should receive penicillin twice daily between the ages of 2 months and at least 5 years of age.1,2 Most children with sickle cell disease are now identified through newborn screening tests, so they can receive special medical care to help prevent complications. More than 40 states screen newborns for sickle cell disease. This alerts physicians to begin treatment before dangerous infections occur.
It is important for babies and children with sickle cell disease to receive regular childhood vaccinations. The Hib (Hemophilus influenzae b) vaccine and the pneumococcal vaccine (Prevnar) help protect against potentially life-threatening bacterial infections. These vaccines are recommended for all babies starting at 2 months of age. Children with sickle cell disease should receive additional vaccinations. These include a yearly flu (influenza) shot, beginning at 6 months of age; another type of pneumococcal vaccine (23-valent pneumococcal vaccine), which protects against additional types of bacteria at 2 and 5 years of age; and the meningococcal vaccine, which protects against meningitis, at age 5.1
Pain episodes. This is the most common symptom of sickle cell disease. Some affected individuals have one or fewer pain episodes a year, while others may have 15 or more.1,2 Pain episodes usually last a few hours to a few days, but they may sometimes last for weeks. Pain can occur in any organ or joint in the body, wherever sickle-shaped cells pile up and block blood vessels. Mild pain episodes can be treated at home with over-the-counter pain medications (such as acetaminophen and ibuprofen) and heating pads. But some pain episodes may be severe and need to be treated in the hospital with strong pain-killing drugs given intravenously (in a vein).
Until recently, there was no effective treatment to prevent the sickling that causes a pain crisis other than blood transfusions. A 1995 study reported that treatment with a drug called hydroxyurea reduced the number of pain episodes in some of the severely affected adults by about 50 percent.3 In 1998, the Food and Drug Administration (FDA) approved the use of this drug in patients over 18 years of age who have had at least three painful episodes in the previous year. A 2003 study that followed the same patients for nine years also found that treatment with hydroxyurea reduced deaths by 40 percent.4
Several smaller studies have found that hydroxyurea is effective and well tolerated in children in the short term. However, the drug is not yet routinely recommended in children because it is not known whether it has any adverse effects on growth and development. Researchers continue to study the long-term safety of the drug in children.
Hand-foot syndrome. Hands and feet may swell when small blood vessels become blocked. This may be the first symptom of sickle cell disease in babies, who also may develop a fever. It usually is treated with pain medication and fluids.
Stroke. If sickle-shaped cells block a blood vessel in the brain, a stroke can result. About 10 percent of children with sickle cell disease have a stroke.5 This can lead to lasting disabilities, including learning problems. Doctors can sometimes identify children who are at increased risk of stroke using a special type of ultrasound examination. In some cases, a doctor may recommend regular blood transfusions to help prevent a stroke. A 1998 study found that regular transfusions greatly reduced the risk of a first stroke in high-risk children with sickle cell disease.5 Regular transfusions also reduced the risk of another stroke in children who already have had a stroke. Unfortunately, regular transfusions pose some major risks— including a potentially fatal buildup of iron in the body and blood-borne infections—so this treatment is not routine. A family and their doctors should decide to attempt this treatment only after a thorough discussion with a pediatric hematologist (doctor who specializes in blood disorders) who is experienced with this treatment. Children who receive regular transfusions also must undergo a complicated and time-consuming treatment aimed at reducing iron levels.
Acute chest syndrome. This is similar to pneumonia, with symptoms such as difficulty breathing, chest pain and fever. It can be caused by an infection or by blocked blood vessels in the lung. This potentially life-threatening disorder should be treated in the hospital. Treatments may include antibiotics, blood transfusions, pain medications, oxygen and medicines that help open up blood vessels and improve breathing.
Vision problems. When tiny blood vessels in the eye become blocked with sickle-shaped cells, vision problems and even blindness can result. Some children with sickle cell disease may need regular eye exams. When eye problems occur, laser treatment often prevents further vision loss.
Slow growth. Children with anemia tend to grow slower than normal and enter puberty later than other children. They also may be pale, have shortness of breath and tire easily.
Can a person catch sickle cell disease from someone who has it?
No. The disease is inherited and is not contagious. To inherit the disease, a child must receive two sickle cell genes, one from each parent.
Do we all have the same chance of inheriting sickle cell disease?
No. In the United States, most cases occur among African-Americans and Hispanic-Americans. About one in every 500 African-Americans has sickle cell disease.6 It also affects people of Arabian, Greek, Maltese, Italian, Sardinian, Turkish and Indian ancestry.
Is sickle cell trait the same thing as sickle cell disease?
No. A person who inherits the sickle cell gene from one parent and the normal type of that gene from the other parent is said to have sickle cell trait. One in 12 African-Americans in this country has sickle cell trait.6 Carriers of the sickle cell gene generally are as healthy as noncarriers. Sickle cell trait cannot change to become sickle cell disease. However, when two people with sickle cell trait have a child, their child may inherit two sickle cell genes and have the disorder.
What are the chances that parents with sickle cell trait will pass it on to their children?
There is a 50 percent chance that a child born to parents who both carry a sickle cell gene will have the trait. There is a 25 percent chance that the child will have sickle cell disease. There also is a 25 percent chance that the child will have neither the trait nor the disease. These chances are the same in each pregnancy.
If only one parent has the trait and the other has no abnormal hemoglobin gene, there is no chance that their children will have sickle cell disease. However, there is a 50-50 chance of each child having the trait.
Can a woman with sickle cell disease have a safe pregnancy?
Yes. However, women with sickle cell disease are at increased risk of complications that can affect their health and that of their babies. During pregnancy, the disease may become more severe and pain episodes may occur more frequently. A pregnant woman with sickle cell disease is at increased risk of preterm labor and of having a low-birthweight baby. However, with early prenatal care and careful monitoring throughout pregnancy, women with sickle cell disease can have a healthy pregnancy. If the baby’s father has sickle cell trait, the baby has a 50 percent chance of having the disease. If he does not, the baby will have only the trait.
Is there a test for sickle cell disease or trait?
Yes. A person can have a blood test to find out if he has either sickle cell trait or a form of the disease. There also are prenatal tests to find out if the baby will have the disease or carry the trait. If both parents have the sickle cell trait, in three out of four cases, the prenatal test will show that the baby will not have sickle cell disease.
Where is sickle cell testing and treatment available?
Couples who are planning to have a baby can get carrier testing at medical centers and sickle cell treatment facilities. A genetic counselor can refer a couple for testing and discuss the risks to their offspring. Other sources of testing and treatment include the hospital pediatric or hematology (blood) departments. Couples also can check with their doctor or the Sickle Cell Disease Association of America for resources in their area.
Is there a cure for sickle cell disease?
A small number of children with severe sickle cell disease have been cured through a blood stem cell transplant. The stem cells (immature cells that develop into blood cells) come from bone marrow, or less frequently from umbilical cord blood, usually donated by siblings who are a good genetic match. Most children with sickle cell disease, however, do not have siblings who are good genetic matches. For this reason, researchers have recently begun performing stem cell transplants using umbilical cord blood from unrelated donors with apparent success.7
About 150 children worldwide with sickle cell disease have had blood stem cell transplants, and about 85 percent of them appear to be cured of the disease.8 However, this approach carries a high risk: about 5 percent of children who underwent bone marrow transplants died.8 The transplant did not cure the disease in another 10 percent.8 Gene therapy may someday offer a cure with less risk.
Currently, researchers are studying a number of new drug treatments, in addition to hydroxyurea, for reducing complications of the disease. Like hydroxyurea, decitabine and butyrate (a food additive) appear to cause the body to make a form of hemoglobin (fetal hemoglobin) that the baby makes before birth.7,9 Increased levels of fetal hemoglobin appear to help prevent red blood cells from sickling. Recent studies also suggest that inhaling the gas nitric oxide or taking an oral dietary supplement called L-arginine (which appears to boost the body’s production of nitric oxide) may also help prevent sickling, as may treatment with an antifungal drug called clotimazole or some blood-thinning drugs.7,9 There has already been a great deal of progress in medical care that reduces serious complications and improves survival in individuals with sickle cell disease. These and other new treatments may further improve the quality of life in affected individuals.
Is the March of Dimes supporting research on sickle cell disease?
The March of Dimes has been a major supporter of sickle cell disease research. Recent grantees have been seeking to develop new treatments to prevent pain episodes and organ damage, including new approaches to gene therapy.
What other sources of information on sickle cell anemia are available?
Information and referral to local groups is available from:
Sickle Cell Disease Association of America
16 S. Calvert Street, Suite 600
Baltimore MD 21202
(800) 421-8453
Sickle Cell Information Center
Box 109
Grady Memorial Hospital
80 Jessie Hill Jr. Drive S.E.
Atlanta GA 30303
(404) 616-3572
National Heart, Lung and Blood Institute Information Center
P.O. Box 30105
Bethesda MD 20824-0105
(301) 592-8573
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