Sickle-shaped red blood cellsAutosomal recessive inheritance
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Sickle-cell disease

Sickle cell disease is a general term for a group of genetic disorders caused by sickle hemoglobin (Hgb S). In many forms of the disease, the red blood cells change shape upon deoxygenation because of polymerization of the abnormal sickle hemoglobin. This process damages the red blood cell membrane, and can cause the cells to become stuck in blood vessels. This deprives the downstream tissues of oxygen and causes ischemia and infarction. The disease is chronic and lifelong. Individuals are most often well, but their lives are punctuated by periodic painful attacks. more...

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In addition to periodic pain, there may be damage of internal organs, such as stroke. Lifespan is often shortened. It is common in people from parts of the world where malaria is or was common, especially in West Africa or in descendents of those peoples. Sickle cell disease can occur in any individual of any color or ethnicity, however.

"Sickle cell anemia" is the name of a specific form of sickle cell disease in which there is homozygosity for the mutation that causes Hgb S. Other forms of sickle cell disease include sickle-hemglobin C disease, sickle beta-plus-thalassemia, and sickle beta-zero-thalassemia. Unlike sickle cell anemia, these other forms of sickle cell disease are compound heterozygous states in which the person has only one copy of the mutation that causes Hgb S and one copy of another abnormal hemoglobin gene. It is important to know that "sickle cell anemia" is the proper name of a specific type of "sickle cell disease", and that "sickle cell disease" is a non-specific term. Because the different forms of sickle cell disease are quite different, one must be sure to specify the exact form of the disease in question.

Signs and symptoms

Patients with sickle cell anemia have steady-state or baseline anemia that varies in severity, with hemoglobin levels of 6-9 g/dl typical. Reticulocyte counts are elevated, reflecting new red blood cells replacing the rapidly destroyed older cells - red blood cell life span is markedly reduced in this disease. Often, the white blood cell and platelet counts are elevated, and these cells may contribute to vaso-occlusion.

Vasoocclusive crises

Vasoocclusive crises are caused by sickled red blood cells that obstruct capillaries and restrict bloodflow to an organ, resulting in ischemia, pain, and organ damage.

Because of its narrow vessels and function in clearing defective red blood cells, the spleen is frequently affected. It is usually infarcted before the end of childhood in individuals suffering from sickle cell anemia. This autosplenectomy increases the risk of infection from encapsulated organisms; preventive antibiotics and vaccinations are recommended for those with such asplenia. Liver failure may also occur with time.

Bone is also a common target of vasoocclusive damage, especially when the bone is particularly weight-bearing. Such damage may result in avascular necrosis (especially of the femur) and bone deterioration. The pain experienced by sickle-cell patients is also due to the bone ischemia.

A recognized type of sickle crisis is the acute chest crisis, a condition characterized by fever, chest pain, and pulmonary infiltrate on chest x-ray. Given that pneumonia and intra-pulmonary sickling can both produce these symptoms, the patient is treated for both conditions. Treatment consists of admission, oxygen, close monitoring, and intravenous antibiotics.

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Sickle cell sufferers living longer, dying less from disease
From Black Issues in Higher Education, 5/20/04

DALLAS

Children with sickle cell disease--an inherited red blood-cell disorder--are living longer, dying less often from their disease and contracting fewer fatal infections than ever before, according to researchers at University of Texas Southwestern Medical Center at Dallas.

Their study, which will appear in the June edition of the scientific journal Blood, is the first to evaluate survival rates of children receiving the most modern treatments for sickle cell disease. It's also one of the largest published sickle cell studies to date. Researchers followed more than 700 Dallas-area children with the disease over two decades.

Thirty years ago, only half of children with sickle cell disease were expected to reach adulthood. This new study showed that patients with sickle cell anemia, the severest and most common form of the disease, had a survival rate of 85.6 percent at 18 years old, and patients with milder forms of sickle cell disease had a survival rate of 97.4 percent at 18. Also, 11.5 percent of patients with sickle cell anemia had a stroke by 18 years old. Although this rate remains constant, fewer children are dying as a result of the stroke, researchers said.

"There weren't any modern or contemporary survival data for children with sickle cell until now," said Dr. Charles Quinn, assistant professor of pediatrics and the study's lead author. "Previous survival studies began in the 1970s, and there have been significant advancements made in the medical care of these children since then."

People with sickle cell disease have a genetic error in their hemoglobin, a component of red blood cells. Instead of being soft and round, the red blood cells of a sickle cell patient are inflexible and sickle-shaped, causing blockages in the blood vessels and preventing body tissues from receiving oxygen.

It is estimated that between 60,000 and 70,000 Americans suffer from the disease. The disease is most common among people of African descent. In the United States, it is estimated that 9 percent of African Americans have the sickle cell trait, and 1 in 600 has sickle cell anemia.

UT Southwestern researchers attribute the improved prognosis to widespread newborn screening that allows physicians to identify the disease early and begin treatment sooner, as well as new types of medicines and vaccines.

Research developments during the past several decades have improved the lives of many persons with sickle cell disease," said Dr. George Buchanan, the study's senior author and director of the National Institutes of Health-funded Southwestern Comprehensive Sickle Cell Center. "Yet the true impact of these investigations on survival of children and adolescents with sickle cell disease has not been clear until now.

"This work gives us contemporary and accurate data confirming the success of our research. It was only a half-century ago that very few persons with sickle cell anemia and related conditions survived beyond 21 years of age," Buchanan said.

COPYRIGHT 2004 Cox, Matthews & Associates
COPYRIGHT 2004 Gale Group

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