cystic fibrosis sĭs´tĭk fībrō´sĭs [key]
, inherited disorder of the exocrine glands (see gland
), affecting children and young people; median survival is 25 years in females and 30 years in males. It is caused by a genetic abnormality in the CF transmembrane conductance regulator (CFTR) gene that results in a misshapen CFTR protein and the consequent disruption of chloride transfer across cell membranes. As a result, chloride ions build up in the cells of the lungs and other organs. Water stays inside the cells to dilute the chloride rather than being drawn out of the cells by normal chloride movement and the normal secretions of the organs thicken. Mucus in the exocrine glands becomes thick and sticky and eventually blocks the ducts of these glands (especially in the pancreas, lungs, and liver), forming cysts. The disease also causes the sweat glands to secrete excessive salt, causing heat prostration in hot weather. Symptoms, which vary according to the severity of the condition and the glands involved, include a distended abdomen; diarrhea; bulky, foul-smelling stools; and malnutrition. Medical problems include nasal polyps and sinus disease, repeated respiratory infections, infertility, liver disease, and diabetes. Diagnosis is confirmed by a sweat test or measurement of transmembrane potential.
Treatment consists of dietary adjustment (low fat–high calorie) and the administration of vitamins, pancreatin, and antibiotics to ward off secondary infections. Special measures are necessary to decrease the viscosity of pulmonary secretions; aerosol application of recombinant human DNase, an enzyme that digests the sticky extracellular DNA that helps form these viscous secretions, was approved in 1993. In some cases lung transplantation (see transplantation, medical) is helpful. The identification of the abnormal gene (1989) paved the way for gene therapy aimed at altering the genetic structure by transferring to the patient cells with normal CFTR genes.
Identification of the genes has also made genetic testing and diagnosis possible. Evolutionary biologists have suggested that the gene, which must be inherited from both parents to cause the disorder, affords carriers some protection against cholera, a disease that kills through profound loss of fluids.
See P. Davis, Cystic Fibrosis (1993); M. E. Hodson and D. M. Geddes, Cystic Fibrosis (1994).
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