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Scientists have learned a great deal about sickle cell anemia during the past 30 years - what causes it, how it affects the patient, and how to treat some of the complications. They also have begun to have success in developing drugs that will prevent the symptoms of sickle cell anemia and procedures that should ultimately provide a cure.
Some researchers are focusing on identifying drugs that will increase the level of fetal hemoglobin in the blood. Fetal hemoglobin is a form of hemoglobin that all humans produce before birth, but most stop making shortly after birth. Most humans have little fetal hemoglobin left in their bloodstream by the time they reach the age of 6 months. However, some people with sickle cell anemia continue to produce large amounts of fetal hemoglobin after birth, and studies have shown that these people have less severe cases of the disease. Fetal hemoglobin seems to prevent sick- ling of red cells, and cells containing fetal hemoglobin tend to survive longer in the bloodstream.
Hydroxyurea appears to work primarily by stimulating production of fetal hemoglobin. There is some evidence that administering hydroxyurea with erythropoietin, a genetically engineered hormone that stimulates red cell production, may make hydroxyurea work better. This combination approach offers the possibility that lower doses of hydroxyurea can be used to achieve the needed level of fetal hemoglobin. However, both of these drugs may produce serious side effects, so researchers continue to search for safer agents that are just as effective.
'Butyrate, a simple fatty acid that is widely used as a food additive, is also being investigated as an agent that may increase fetal hemoglobin production.
Clotrimazole, an over-the-counter medication commonly used to treat fungal infections, is under investigation as a treatment to prevent the loss of water from the red blood cells that contributes to sickling. It is hoped that this medication, used alone or in conjunction with other anti-sickling agents, may eventually offer an effective long-term therapy for sickle cell anemia patients.
Bone marrow transplantation has been shown to provide a cure for severely affected children with sickle cell disease. Although many of the risks of this procedure have been reduced, it still is not entirely without risk. In addition, the marrow must come from a healthy matched sibling' donor, and only about 18 percent of children with sickle cell anemia are likely to have a matched sibling. Researchers are working on techniques to further reduce some of the risks of bone marrow transplantation for patients with sickle cell disease.
The ultimate cure for sickle cell anemia may be gene therapy. In sickle cell anemia, the gene which switches on production of adult hemoglobin shortly before birth is defective. Two approaches to gene therapy are being explored. Some scientists are looking into whether correcting this gene and inserting it into the bone marrow of people with sickle cell anemia will result in the production of normal adult hemoglobin. Others are looking at the possibility of turning off the defective gene and simultaneously reactivating another gene that turns on production of fetal hemoglobin. In both cases, the research is at a very early stage. Progress is being made, however, and there is a real possibility of an eventual clinical cure for sickle cell anemia.
Although the genetic defect that causes sickling was identified more than 40 years ago, until very recently, research into the development of treatments for the disease was hampered by the lack of an animal model that could be used to test experimental drugs and gene therapy. Recently, however, scientists were able to genetically engineer a line of mice that exhibit some of the characteristics of sickle cell disease in much the same way humans do. This is an important advance in the search for an effective treatment and eventual cure for sickle cell disease.
