sickle cell anemia Human autosomal recessive disease that causes production of abnormal red blood cells that collapse (or sickle) and cause circulatory problems.
autosomes The chromosomes other than the sex chromosomes. Each member of an autosome pair (in diploid organisms) is of similar length and in the genes it carries.
recessive Refers to an allele of a gene that is expressed when the dominant allele is not present. An allele expressed only in homozygous form, when the dominant allele is absent.
location of hemoglobin hemoglobin A red pigment in red blood cells that can bind with oxygen and is largely responsible for the blood's oxygen-carrying capacity. Hemoglobin is composed of four polypeptide chains, two alpha (a) and two beta (b) chains.
InfoPlease.com********** sick'le cell" ane'mia Pathol. a chronic hereditary blood disease, occurring primarily among Africans or persons of African descent, in which abnormal hemoglobin causes red blood cells to become sickle-shaped and nonfunctional, characterized by enlarged spleen, chronic anemia, lethargy, weakness, joint pain, and blood clot formation. Also called sick€le€mi€a Pronunciation: (sik"u-lE'mE-u, sik-lE'-). [key]
sick'le cell" trait" Pathol. the usually asymptomatic hereditary condition that occurs when a person inherits from only one parent the abnormal hemoglobin gene characteristic of sickle cell anemia. Also called sicklemia.
sick'le cell" Pathol. an abnormal red blood cell having an elongated, crescentlike shape due to the presence of an abnormal hemoglobin.
sickle cell disease sickle cell disease or sickle cell anemia,inherited disorder of the blood in which the oxygen-carrying hemoglobin pigment in erythrocytes (red blood cells) is abnormal. This ³hemoglobin-S² crystallizes in small capillaries, where the concentration of oxygen in the blood is low (but sufficient for normal hemoglobin), causing the red blood cells to assume distorted, sicklelike shapes. Linus Pauling discovered the chemical abnormality of the hemoglobin molecule that causes the erythrocyte sickling in 1949.
The sickled red blood cells tend to clog small blood vessels, depriving the tissues they serve of blood and oxygen. Painful ³crises² result, with symptoms depending on the site affected (e.g., joint and abdominal pain or kidney damage). Strokes or seizures can occur if the brain is affected. Lung infections resulting from the patient's disinclination to take painful deep breaths are a frequent complication. In addition, the sickled erythrocytes ar fragile and subject to rupture and destruction, leading to hemolytic anemia (reduction of oxygen-carrying hemoglobin caused by premature destruction of red blood cells) and such symptoms as fatigue, jaundice, and headaches.
hemoglobin [hE'muglO"bin] hemoglobin , respiratory protein found in the red blood cells (erythrocytes) of all vertebrates and some invertebrates. A hemoglobin molecule is composed of a protein group, known as globin, and four heme groups, each associated with an iron atom.
In the lungs, each iron atom combines reversibly with a molecule of oxygen. Each hemoglobin molecule also has attached a single cysteine amino acid, which attracts nitric oxide from the lungs. The enriched hemoglobin circulates and is carried through the body to the tissues, where the nitric oxide dilates the small capillaries, allowing hemoglobin to deliver its oxygen to the tissues. Then the oxygen- and nitric oxidefree hemoglobin molecule picks up carbon dioxide and free nitric oxide and transports both back to the lungs, where they are exhaled as waste.
Hemoglobin is produced in bone marrow by erythrocytes and is circulated with them until their destruction. It is then broken down in the spleen, and some of its components, such as iron, are recycled to the bone marrow. Other components, such as the heme groups, are broken down into bilirubin, transported to the liver, and secreted with the bile into the intestine for eventual elimination from the body.
Hemoglobin deficiency may be a result of structural abnormality in the hemoglobin molecules themselves. In sickle cell disease, this structural abnormality creates malformed red blood cells which clog blood vessels, severely restricting the supply of blood flowing to body tissues.
Encyclopedia‹sickle cell disease
Treatment There is no cure for the disease, but advancements in treatment have improved median survival to 42 years for men and 48 years for women. Cerebral hemorrhage or shock is the usual cause of mortality in children. Recent studies have indicated that regular blood transfusions can prevent strokes in children. Anemia is treated with folic acid. Sickle cell crises may be treated with intravenous hydration, pain medication, antibiotics, oxygen, and transfusions.
Hydroxyurea, formerly used as a cancer treatment, has been helpful to many adults with the disease, lessening the frequency and severity of crises. New drugs for reducing the severity of crises are being tested as well. One acts as a lubricant, allowing sickled cells to flow more easily through tiny vessels. The other helps to prevent tissue deprived of blood from dying during a crisis.
Incidence The disease is confined mainly to blacks, especially those of W African descent, but it also occurs in persons of Mediterranean, Middle Eastern, and Indian origin. The mutation may at one time have had an advantageous effect; those afflicted with the abnormality have a higher survival rate in malaria-infested zones.
Under normal circumstances the disease occurs only in those patients who inherit the gene for the abnormal hemoglobin from both parents. This so-called homozygous form of the disease occurs in 1 in 400 African Americans. About 8% of African Americans have sickle cell trait; that is, they are heterozygotes, usually symptomless carriers who have inherited a normal hemoglobin gene from one parent and hemoglobin-S from the other.
There are also intermediate forms of the disease that result when a gene for hemoglobin-S is inherited from one parent and a gene for any of several other abnormal kinds of hemoglobin is inherited from the other. Genetic screening is recommended for prospective parents at risk of passing on the disease. If both parents are carriers (i.e., have sickle cell trait), then each child has a one in four chance of having sickle cell disease. genetic screening genetic screening, testing for genetic disorders. Most commonly, prospective parents or a fetus is tested when a specific genetic disorder is suspected (e.g., Tay-Sachs or sickle cell disease). In such a case, genetic screening begins with a complete medical history of both parents. If the parents decide to conceive or have already conceived, diagnostic tests, such as chorionic villus sampling and amniocentesis, can be performed on the fetus to detect various genetic disorders. In the case of a positive finding, the parents can elect to abort the fetus. Embryo biopsy, another diagnostic test, can be used on an embryo conceived by in vitro fertilization to determine if the embryo is free of certain genetic diseases before it is implanted in the uterus.
As researchers identify more genetic markers for diseases and develop blood tests for them, concern has arisen over the use of such tests to deny people health and life insurance, employment, and the like. A 1993 National Academy of Sciences report called for the establishment of ethical guidelines on the use of genetic screening, and in 1995 the Equal Employment Opportunity Commission said that the use of genetic screening to deny employment could violate the Americans with Disabilities Act.
See also eugenics.
Diagnosis of Inherited Disorders DNA fingerprinting is used to diagnose inherited disorders in both prenatal and newborn babies in hospitals around the world. These disorders may include cystic fibrosis, hemophilia, Huntington's disease, familial Alzheimer's, sickle cell anemia, thalassemia, and many others.
Early detection of such disorders enables the medical staff to prepare themselves and the parents for proper treatment of the child. In some programs, genetic counselors use DNA fingerprint information to help prospective parents understand the risk of having an affected child. In other programs, prospective parents use DNA fingerprint information in their decisions concerning affected pregnancies.
DNA Fingerprinting in Human Health and Society Written by David F. Betsch, Ph.D., Biotechnology Training Programs, Inc. Edited by Glenda D. Webber, Iowa State University Office of Biotechnology. *
******** hemoglobin http://esg-www.mit.edu:8001/esgbio/lm/proteins/structure/structure.html
******* eugenics [yOOjen'iks] eugenics , study of human genetics and of methods to improve the inherited characteristics, physical and mental, of the human race. Efforts to improve the human race through bettering housing facilities and other environmental conditions are known as euthenics.
Sir Francis Galton, who introduced the term eugenics, is usually regarded as the founder of the modern science of eugenics; his emphasis was on the role of factors under social control that could either improve or impair the qualities of future generations. Modern eugenics is directed chiefly toward the discouragement of propagation among the unfit (negative eugenics) and encouragement of propagation among those who are healthy, intelligent, and of high moral character (positive eugenics). Such a program involves many difficulties, especially that of defining which traits are most desirable.
The first half of the 20th cent. saw extreme coercive application of such principles by governments ranging from miscegenation laws and enforced sterilization of the insane in the United States and other nations to the Holocaust of Nazi Germany. Regulated eugenics continues in some parts of the world; China enacted restrictions on marriages involving persons with certain disabilities and diseases in 1994.
In the United States in recent years, interest in eugenics has centered around genetic screening. It is known, for example, that hemophilia, albinism, and certain structural abnormalities are inheritable. Family gene maps, called pedigrees, can help families with serious diseases avoid having children with the same diseases through genetic counseling, and, increasingly, prospective parents can be tested directly for the presence of undesired genes. If conception has occurred, tests such as amniocentesis and chorionic villus sampling can be used to detect certain genetic defects in the fetus.
See J. H. Bennett, Natural Selection, Heredity, and Eugenics (1983); D. J. Kevles, In the Name of Eugenics (1986); M. B. Adams, ed., The Wellborn Science: Eugenics in Germany, France, Brazil, and Russia (1989).
********* Human Genome Project a federally funded U.S. scientific project to identify both the genes and the entire sequence of DNA base pairs that make up the human genome.
Encyclopedia
Sickle Cell Trait: Sickle cell trait means that you have different hemoglobin in addition to the common type. Hemoglobin is the component of our red blood cells that carries oxygen from the lungs to all the other parts of the body. Most people have only hemoglobin A. In contrast, people with sickle cell trait have both hemoglobin A and hemoglobin S. Hemoglobin S is very similar to hemoglobin A except for one change in its structure. There are many other types of hemoglobin that are also different from the common type: C, D, and E.
Health Concerns: Sickle cell trait rarely causes any health problem. There are only two exceptions that should be mentioned: first when individuals with the sickle cell trait are exposed to low oxygen pressure they may experience a painful episode, an example of this is flying in an unpressurized aircraft. The second exception is possible minute kidney problems. Other than these two exceptions individuals with sickle cell live a normal life.
Sickle Cell Disease: When an individual has only hemoglobin S and no hemoglobin A, then he or she has sickle cell disease. When red blood cells containing hemoglobin S release their oxygen to the tissues, they change shape from round to sickled. This impairs their passage through the small blood vessels. Since red blood cells are very important in delivering oxygen to all the body, many organs can be affect along with their growth. Sickle cell disease may be a severe disease. Although it cannot be cured, effective treatment is available for persons with sickle cell disease.
Spread of the Disease: The trait and the disease are inherited. Therefore they can be passed to your children. The most important thing is to make sure that you get tested. If you have sickle cell trait and your partner does not, your children each have a 50% chance of having the sickle cell trait, and a 50% chance of having normal hemoglobin. If you have sickle cell trait it is extremely important that your partner is tested. If you and your partner both have sickle cell trait there is a 25% chance of the child having normal hemoglobin, a 50% chance of the child having the sickle cell trait, and a 25% of having sickle cell disease. If both you and your partner have sickle cell trait, and want to know whether the unborn child has sickle cell disease testing can be performed as early as the tenth week of pregnancy. If the results are normal, the parents can be reassured. If the tests show the baby will be affected, the parents can be better prepared and they can make and informed decisions regarding the pregnancy.