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Sickle cell disease is a group of disorders that affects hemoglobin, the molecule in red blood cells that delivers oxygen to cells throughout the body. People with this disorder have atypical hemoglobin molecules called hemoglobin S, which can distort red blood cells into a sickle, or crescent, shape.
Signs and symptoms of sickle cell disease usually begin in early childhood. Characteristic features of this disorder include a low number of red blood cells (anemia), repeated infections, and periodic episodes of pain. The severity of symptoms varies from person to person. Some people have mild symptoms, while others are frequently hospitalized for more serious complications.
The signs and symptoms of sickle cell disease are caused by the sickling of red blood cells. When red blood cells sickle, they break down prematurely, which can lead to anemia. Anemia can cause shortness of breath, fatigue, and delayed growth and development in children. The rapid breakdown of red blood cells may also cause yellowing of the eyes and skin, which are signs of jaundice. Painful episodes can occur when sickled red blood cells, which are stiff and inflexible, get stuck in small blood vessels. These episodes deprive tissues and organs of oxygen-rich blood and can lead to organ damage, especially in the lungs, kidneys, spleen, and brain. A particularly serious complication of sickle cell disease is high blood pressure in the blood vessels that supply the lungs (pulmonary hypertension). Pulmonary hypertension occurs in about one-third of adults with sickle cell disease and can lead to heart failure.
Sickle cell disease affects millions of people worldwide. It is most common among people whose ancestors come from Africa; Mediterranean countries such as Greece, Turkey, and Italy; the Arabian Peninsula; India; and Spanish-speaking regions in South America, Central America, and parts of the Caribbean.
Sickle cell disease is the most common inherited blood disorder in the United States, affecting 70,000 to 80,000 Americans. The disease is estimated to occur in 1 in 500 African Americans and 1 in 1,000 to 1,400 Hispanic Americans.
Mutations in the HBB gene cause sickle cell disease.
Hemoglobin consists of four protein subunits, typically, two subunits called alpha hemoglobin and two subunits called beta hemoglobin. The HBB gene provides instructions for making beta hemoglobin. Various versions of beta hemoglobin result from different mutations in the HBB gene. One particular HBB mutation produces an abnormal version of beta hemoglobin known as hemoglobin S (HbS). Other mutations in the HBB gene lead to additional abnormal versions of beta hemoglobin such as hemoglobin C (HbC) and hemoglobin E (HbE). HBB mutations can also result in an unusually low level of beta-hemoglobin; this abnormality is called beta thalassemia.
In people with sickle cell disease, at least one of the beta hemoglobin subunits in hemoglobin is replaced with hemoglobin S. In sickle cell anemia, which is a common form of sickle cell disease, hemoglobin S replaces both beta hemoglobin subunits in hemoglobin. In other types of sickle cell disease, just one beta hemoglobin subunit in hemoglobin is replaced with hemoglobin S. The other beta hemoglobin subunit is replaced with a different abnormal variant, such as hemoglobin C. For example, people with sickle-hemoglobin C (HbSC) disease have hemoglobin molecules with hemoglobin S and hemoglobin C instead of beta hemoglobin. If mutations that produce hemoglobin S and beta thalassemia occur together, individuals have hemoglobin S-beta thalassemia (HbSBetaThal) disease.
Abnormal versions of beta hemoglobin can distort red blood cells into a sickle shape. The sickle-shaped red blood cells die prematurely, which can lead to anemia. Sometimes the inflexible, sickle-shaped cells get stuck in small blood vessels and can cause serious medical complications.
This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. Most often, the parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but do not show signs and symptoms of the condition.
ICAgen, Inc. - Discovers and develops pharmaceutical products to treat medical conditions such as atrial fibrillation, urinary incontinence, central nervous system disorders, and sickle cell disease.
CytRx Corp. - Develops products used to treat acute sickle cell crisis, vascular diseases, and technologies to improve effectiveness of vaccines, gene and drug delivery, and growth supplements. Based in Los Angeles, California. (Nasdaq: CYTR)
Sickle Cell Disease Association of America - Education, advocacy and other initiatives which promote awareness and support for sickle cell programs and patients.
My Sickle Cell Homepage - Provides a first hand look at Sickle Cell Anemia, built by a person suffering from the disease. Frequently asked questions and a personal diary of the owner's own battle with this disease.
Joint Center for Sickle Cell and Thalassemic Disorders - Gives an evaluation of the causes and treatments of sickle cell disease as well as current research. Information is available both for lay persons as well as health care providers.
Natural History of Sickle Cell Disease in India - Lists and describes the contribution of Dr. Bimal Chandra Kar. Patient resources, papers and publications.
Sickle Cell Disease Review - Promotes and disseminates research into the scientific, clinical and social aspects of this disorder. Literature review, bibliography, and general information on the disease.
The Sickle Cell Foundation of Alberta - Educates the public about sickle cell disease and provides support for carriers of the trait and their families.
Sickle Cell Disease - Information for school personnel.
Sickle Cell Disease: Practical Tips for Preventing a Sickle Cell Crisis - Advice from FamilyDoctor.org.