None — Sickle Cell Disease
Sickle cell disease is a condition in which some of the red blood cells are abnormally shaped. Red blood cells contain hemoglobin, a protein that carries molecules of oxygen. Normally, the red blood cells are round and flexible so they can easily squeeze through narrower blood vessels. Patients with sickle cell disease have red blood cells that contain an abnormal form of hemoglobin, which causes some of the cells to become shaped like a sickle, or the letter "C." These cells are less flexible and can become trapped in narrower blood vessels. Sometimes the cells bunch together and form a clump that gets stuck in the vessel. When the blood flow is blocked, areas of tissue beyond that point are deprived of oxygenated blood.
According to the Centers for Disease Control and Prevention, up to 100,000 Americans have sickle cell disease. In the U.S., the condition is more common in African-Americans (occurring in one out of every 500 births) and Hispanics (one out of every 36,000 births).
Sickle cell disease is a genetic condition. However, in order for a child to develop it, he/she must acquire two copies of the sickle cell gene – one from each parent. If the child only inherits one copy, he/she will have the sickle cell trait (i.e., become a carrier, but won't get the disease). When both parents have sickle cell trait, a child has a two percent chance of developing sickle cell disease and a 50 percent chance of developing sickle cell trait.
Sickle Cell Complications
Patients with sickle cell disease can develop several different kinds of complications. A blocked vessel causes pain because the tissues aren't getting enough oxygen. The most common locations of blockages are the bones, lungs, abdomen and joints. The pain can range from mild to severe and last from hours to days. In some cases, the blockage can lead to organ damage. Blockages in the hands or feet cause a condition called hand-foot syndrome. Clumping of sickle cells in the lung causes a life-threatening condition called acute chest syndrome. In the brain, the blockage can lead to a stroke. Sickle cells can also block blood flow in the eyes, causing damage to the retina and potential vision loss.
Sickle cell disease can also lead to a decrease in oxygen levels in the blood (a condition called anemia) because the abnormal cells usually only live for about 10 to 20 days (compared to about 120 days for a healthy red blood cell). As the sickle cells die off, the body can't make replacements fast enough, causing a drop in hemoglobin levels. Signs of anemia include: tiredness, irritability, dizziness, rapid heart rate, breathing problems, jaundice and growth problems.
Treating Sickle Cell Disease
The goals of treatment for sickle cell disease are to relieve pain, manage complications and prevent infections. A daily medication called, hydroxyurea, may help reduce or prevent serious pain episodes. Some patients also benefit from regular blood transfusions.
Currently, the only cure for sickle cell disease is a bone marrow transplant. In this procedure, heavy doses of chemotherapy are given to destroy the patient's own bone marrow. Then, the patient is given a transfusion of healthy, donor marrow cells. Hopefully, these donor cells will migrate to the bone marrow and begin producing new blood cells, including normal red blood cells.
A bone marrow transplant is a very risky procedure. The chemotherapy drugs can damage the liver and cause severe liver problems or death. In addition, patients are at high risk for infection for many months after the transplant. Because of the risks involved with bone marrow transplant, the treatment is typically only offered for patients with chronic or severe complications. Another factor affecting bone marrow donation is that the donor marrow must come from a closely matched healthy donor. Often such a donor can't be found.
Reduced Intensity Conditioning
Researchers at The Children's Hospital of Philadelphia are testing a new technique to prepare patients for bone marrow transplants, called "reduced intensity conditioning." Nancy Bunin, M.D., Marrow Transplant Director, explains that, instead of chemotherapy, patients get high doses of immune-suppressing drugs. These drugs work by destroying only the patient's immune system cells. That prevents the donor marrow cells from being recognized as "foreign" and being destroyed.
Conditioning takes about one week in the hospital. Then, the transplant is given. Bunin says patients stay in the hospital until they recover from the transplant, generally for about two to four weeks. Once they go home, the patients must remain in isolation for several months to reduce risk for serious infections (because the immune system had been wiped out).
The long-term benefits of reduced intensity conditioning for bone marrow transplant are still not known. Although the process is considered a cure for sickle cell disease, it will not reverse damage that has already been done. However, Bunin believes it may enable treated patients avoid serious future complications and improve survival rates to a near-normal life span.
Although reduced intensity conditioning is less toxic and risky than traditional chemotherapy for bone marrow transplants, the therapy will still only be offered to selected patients. In addition, many patients don't have a suitable marrow donor. Bunin asks that anyone who would consider becoming a donor, register with the Be the Match, National Marrow Donor Program. Information is available here.
Reduced intensity conditioning in preparation for bone marrow transplant is currently being tested for several different conditions. For information about the study, click here, then type the trial identification number in the search box: NCT01050855.
For information on sickle cell disease:
Centers for Disease Control and Prevention March of Dimes National Heart, Lung and Blood Institute Sickle Cell Disease Association of America
For information on becoming a bone marrow donor or signing onto the registry: