LYCOS RETRIEVER 
Cystic Fibrosis: Cystic Fibrosis Mutation
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Cystic Fibrosis can be identified before birth through prenatal screening and after birth through newborn screening. In 2001, the American College of Obstetricians and Gynecologists recommended that pregnant women be offered screening for CFTR mutations. Currently, 20 percent of pregnant women in the United States receiving prenatal care are being screened for CF.8
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Cystic fibrosis was first described as a disease in the late 1930s by Dorothy Hansine Andersen. It is the most common genetic disease among people with European ancestry. Approximately one in every 25 people of European descent is a carrier of one of the cystic fibrosis mutations, having one normal gene and one CF gene. Since cystic fibrosis is recessive, both copies of the gene have to be CF genes to cause the symptoms that occur in about 1 in every 2500 children. The high incidence of this lethal gene can be explained by the fact that CF carriers, who don't show any symptoms, enjoy some protection against cholera, since the extreme water loss in the intestines is prevented. More recently, evidence suggests CF genes could give protection against typhoid fever.
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Cystic fibrosis occurs when there is a mutation in the CFTR gene. The protein created by this gene is anchored to the outer membrane of cells in the sweat glands, lungs, pancreas, and other affected organs. The protein spans this membrane and acts as a channel connecting the inner part of the cell (cytoplasm) to the surrounding fluid. This channel is primarily responsible for controlling the movement of chloride from inside to outside of the cell. When the CFTR protein does not work, chloride is trapped inside the cell in the lung and outside in the skin. Because chloride is negatively charged, positively charged ions ... cannot cross into the cell because they are affected by the electrical attraction of the chloride ions.
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Cystic fibrosis (CF) causes early death for most homozygotes, yet has a carrier frequency among Caucasians of about 4-5%, suggesting a heterozygote advantage. The major defect in the CF gene is a three-base deletion leading to loss of a phenylalanine residue at position 508 (delta F508) that accounts for about 68% of CF alleles in the North American population; the remaining 32% appears to consist of a large assortment of mutations. Sweat secretion in response to beta-adrenergic stimulation is completely lacking in CF homozygotes and is reduced to 1/2 normal in heterozygotes. To determine if this secretory process is affected by different CF alleles, we used the polymerase chain reaction technique with DNA obtained from peripheral leukocytes to determine retrospectively the presence or absence of the delta F508 allele in 20 CF heterozygotes for whom sweat responses to beta-adrenergic stimulation had previously been determined. Twelve of 20 subjects (60%) were positive for the delta F508 mutation. The variance in sweat responses was not reduced in the delta F508 group relative to the non- delta F508 group, but a gender/allele interaction was noted.
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Cystic fibrosis is the most common life-limiting autosomal recessive disease among people of European heritage. In the United States, approximately 30,000 individuals have CF; most are diagnosed by six months of age. Canada has approximately 3,000 citizens with CF. Approximately 1 in 25 people of European descent and 1 in 22 people of Ashkenazi Jewish descent is a carrier of a cystic fibrosis mutation. Although CF is less common in these groups, approximately 1 in 46 Hispanics, 1 in 65 Africans and 1 in 90 Asians carry at least one abnormal CFTR gene.[52][53][54]
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Cystic fibrosis results when a person inherits two defective copies (mutations) of a particular gene. This gene controls the production of a protein that regulates the transport of chloride and sodium (salt) across cell membranes. Worldwide, about 3 of 100 white people carry one defective copy of the gene; ... they are carriers but they themselves do not get sick. About 3 of 10,000 white people inherit two defective copies of the gene; thus, they develop cystic fibrosis. In these people, chloride and sodium transport is disrupted and dehydration and increased stickiness of secretions occur.
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Cystic Fibrosis Mutation