SICKLE CELL ANAEMIA

What Is it?

It is an inherited disease of red blood cells which can cause attacks of pain and damage to vital organs and can lead to early death. Sickle cell disease affects a protein inside the red blood cells called hemoglobin.

Hemoglobin in the red blood cells carries oxygen from the lungs and takes it to every part of the body. The main hemoglobin in the red blood cells of people with sickle cell disease is different from the usual hemoglobin. Red blood cells containing mainly normal hemoglobin are round and flexible. But when oxygen is released by the red blood cells in people with sickle cell disease, the abnormal hemoglobin forces the cells to become distorted and rigid, often looking like the C-shaped farm tool called a sickle.

Sickle cells tend to become trapped and to be destroyed in the liver and in the spleen. This results in a shortage of red blood cells, or anemia, which, when severe, can cause an affected person to be pale, short of breath and easily tired. Certain conditions, such as enlargement of the spleen and infections, may worsen the anemia by speeding up destruction of red blood cells. Infections also can reduce red blood cell production.

There are several forms of sickle cell disease. The most common forms are referred to as SS (the child inherits two sickle cell genes), SC (the child inherits one sickle cell gene and one gene for another abnormal type of hemoglobin called "C"), and S beta-zero thalassemia (the child inherits one sickle cell gene and one gene for a type of thalassemia, another inherited anemia). The effects of sickle cell disease vary greatly from one person to the next. Some affected people rarely are ill while others are frequently hospitalized.

Who gets it?

The disease is inherited and is not contagious. To inherit the disease, a child must receive two sickle cell genes, one from each parent who "carries" a sickle cell gene.

In the United States, most cases of sickle cell disease occur among African-Americans, and Hispanics of Caribbean ancestry. About one in every 400 African-Americans has sickle cell disease. It also affects people of Arabian, Greek, Maltese, Italian, Sardinian, Turkish and Indian ancestry.

There is a 50 percent chance that a child born to a couple who both carry a sickle cell gene will have the trait, like the parents. 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.

Each successive pregnancy has the same set of chances. 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.

What are the symptoms?

Infants and young children with sickle cell disease are especially vulnerable to severe bacterial infections, such as those that cause meningitis and blood infection (septicemia). Infections are the leading cause of death in children with sickle cell disease. However, early diagnosis and treatment dramatically reduce the risk of infections and death.

In 1987, a National Institutes of Health panel recommended that all babies be screened at birth for sickle cell disease. All states now screen babies' blood for two or more inherited diseases, and the test for sickle cell disease is done using the same blood sample. To date, more than 40 states are testing newborns for sickle cell disease.

Newborn testing alerts physicians to begin treatment before dangerous infections occur. Studies show that daily treatment with the antibiotic penicillin, beginning by 2 months of age and continuing to about 5 years, reduces the risk of the most serious infections by about 85 percent.

It is very important for babies and children with sickle cell disease to receive the regular childhood vaccinations. One of these vaccinations, the Hib (Hemophilus influenzae b) vaccine, which is recommended for all babies starting at 2 months of age, helps protect against a potentially life-threatening bacterial infection. It also is important that children with sickle cell disease receive the pneumococcal and meningococcal vaccines (to prevent septicemia and meningitis) at ages 2 and 5 years or older. They also should have yearly flu (influenza) shots beginning after 1 year of age.

At times, sickle cells become stuck in tiny blood vessels. When they get stuck, the cells pile up and block the blood vessels. This cuts off the blood supply to nearby tissues so that no cells can get through to bring oxygen to them. Without oxygen, the area becomes inflamed and starts to hurt. This blockage of blood vessels is known as a sickle cell pain episode or "crisis." Pain episodes may be very severe and need to be treated in the hospital with pain-killing drugs or, more often, they are milder and can be treated at home. If the blockage is long-lasting, it can destroy areas of tissue.

Sickle cell pain occurs most frequently in bones. Until recently, there was no effective treatment to prevent the sickling that causes a pain crisis. A 1995 study reported that treatment with a drug called hydroxyurea reduced the number of pain crisis in severely affected adults by about 50 percent. However, this drug is not yet recommended for affected children. Studies looking into the safety of this drug for children are currently under way.

What tests will the Doctor want to do?

Readily available blood tests such as hemoglobin electrophoresis, can identify people who have either sickle cell trait or a form of the disease, as well as a number of other inherited hemoglobin abnormalities. There also is a prenatal test to determine whether the baby will have sickle cell disease, carry the trait, or be unaffected. In three out of four cases, if both parents carry the sickle cell gene, the prenatal test will reveal that the fetus will not have sickle cell disease.

Couples who are planning to have a baby can get carrier testing at medical centers and sickle cell treatment facilities. A genetic counselor at the nearest medical center can refer a couple for testing and discuss the risks to their offspring.

Other sources of testing and counseling, as well as treatment of those with sickle cell disease, include the pediatric department or hematology (blood) division of your local hospital.

What is the treatment?

A few children with sickle cell disease have been cured through a bone marrow transplant, using donated bone marrow from an immunologically matched sibling. However, a cure using this approach carries a high risk: About 5 to 8 percent of children who undergo bone marrow transplants for severe hemoglobin disorders die. Other approaches that are being studied, such as gene therapy, may someday offer a cure at less risk.

Currently, a number of new therapies, including hydroxyurea, for reducing the severity and frequency of complications of the disease are being tried. There also has been much progress in medical care that limits damage to the organs from sickling. This care has greatly improved survival and the quality of life for many affected individuals.