Cystic Fibrosis
A genetic disorder that causes a thick mucus to build up in the respiratory system and in the pancreas, a digestive organ. People with cystic fibrosis are highly susceptible to respiratory infections and are typically malnourished due to the malfunctioning of the pancreas.
One of every 25 babies born in the United States is affected with cystic fibrosis, the most common fatal genetic disease in the nation. The average life expectancy of people with cystic fibrosis is 29 years. Only 10% of people with the disease survive into their 30s. Ninety-five percent of cystic fibrosis deaths are caused by lung complications; the other 5% are due to liver failure.
Most cases of cystic fibrosis are caused by a defective gene that must be carried by both parents to produce a child with cystic fibrosis. It is estimated that one in every 20 Americans carries the defective gene. When two carriers have a child, there is one in two chance the child will carry the gene but not have cystic fibrosis, one in four chance the child will not even have the gene, and one in four chance the child will have cystic fibrosis. In most cases, cystic fibrosis is diagnosed by the age of three. Repeated colds and respiratory infections, coughing, and abnormally low weight gain may be present from birth. Other problems such as pneumonia or asthma may precede the diagnosis. Some children become very ill and survive for only a few years.
In 1989, a team of researchers located the defective cystic fibrosis gene, which causes production of a defective version of an important protein called the CF transmembrane conductance regulator (CFTCR), whichperforms a crucial function in airway and pancreas cells. The protein works as a pump within the cell membrane, regulating the movement of sodium and chloride (the components of salt) in and out of cells. In people with cystic fibrosis, however, this pump does not work and water is retained within the cells, depriving the tissues of much-needed moisture. A dry, sticky mucus builds up in the airway and the pancreas, obstructing breathing and interfering with digestive processes. The mucus also clogs sweat glands and salivary glands.
People afflicted with cystic fibrosis have trouble breathing and are highly susceptible to bacterial infections of the lungs. Normally, bacteria are expelled from the lungs by coughing and the movement of thin mucus up the airways to the throat where the bacteria are expelled. But in people with cystic fibrosis the mucus is too thick to be moved and bacteria are able to inhabit the lungs and cause infection. Children with cystic fibrosis often become infected with such bacteria as Streptococcus pneumoniae, Hemophilus pneumoniae, and Staphylococcus aeureus. Adults are most susceptible to Pseudomonas aeurginosa. A rare type of bacteria, Pseudomonas cepacia, currently infects people with cystic fibrosis at alarming rates. P. cepacia causes a severe infection and hastens lung damage, leading to earlier death.
In addition to lung disease, people with cystic fibrosis have digestive disorders due to the thick mucus that clogs the pancreas. The pancreas secretes enzymes during digestion that break down food so that the body can absorb nutrients. But with cystic fibrosis, this function is impaired. People with the disease are typically thin and malnourished due to malabsorption of nutrients. Liver disease and diabetes may also occur with cystic fibrosis.
Cystic fibrosis is diagnosed with a "sweat test," a simple procedure that measures the amount of salt in the patient's perspiration. A high level of salt indicates cystic fibrosis. Currently no definitive cure for cystic fibrosis exists. Treatment of the disease focuses on alleviating symptoms caused by the build-up of mucus.
To combat the lung infections that accompany cystic fibrosis, many people with the disease periodically take courses of antibiotics as a preventive measure. Some people undergo a course of antibiotics four times a year. Mucus in the lungs can also be broken down by drugs called mucolytic agents. These agents can be taken as pills but some are manufactured in the form of aerosols and are inhaled.
Clearing the thick mucus from the lungs can also be accomplished by physiotherapy. Physiotherapy includes breathing exercises and percussion, the administration of blows to the back and chest to loosen the mucus. Some people with cystic fibrosis perform percussion on themselves but it is most effective when performed by someone else. In patients who can tolerate it, vigorous exercise has been shown to improve fitness and well-being, as it also loosens the thick secretions.
To control the malabsorption of nutrients, people with cystic fibrosis take pancreatic enzymes in pill form with every meal. A diet high in fat, protein, and carbohydrates is also recommended to boost the nutrients that a cystic fibrosis sufferer receives. Multi-vitamins can also help prevent deficiencies of certain vitamins. When these methods do not result in adequate weight gain, some people supplement their diets with tube feedings in which a nutrient-rich solution is infused through a tube placed in the stomach.
Researchers hope that the discovery of the gene responsible for cystic fibrosis will lead to a genetic approach to curing the disease. In gene therapy, a normal gene is inserted into cells to replace the defective gene. The lung and pancreas cells are most affected by the disorder and must receive the new gene. Once inside, the normal gene encodes for the correct protein. In most gene therapy experiments, cells from an affected organ are removed from the body and infected with a virus that has been induced to carry the normal gene. The newly infected cells are then put back into the body. In treating cystic fibrosis, however, this method has failed, and researchers are currently working on an approach in which the patient inhales the gene-carrying virus directly.
In 1994, researchers successfully transferred a virus containing the normal CFTCR gene into four cystic fibrosis patients. The patients inhaled the virus into the nasal passages and lungs. An adenovirus, the virus used to carry the gene, is considered relatively harmless to human beings. Nevertheless one patient in this experiment developed viral-infection symptoms, including headache, fatigue, and fever. Data is currently being collected on whether the experiment affected the mucus production in the lungs of the subjects.
Before gene therapy for cystic fibrosis is perfected, researchers must overcome several obstacles. The most important obstacle is the use of viruses as carriers for the normal genes. Some scientists contend that using viruses is simply too dangerous, especially for patients who already have a chronic debilitating disease. Furthermore, the genetic material of viruses is small compared to human genetic material and thus can mutate quickly. If a virus undergoes a mutation, a small chance exists that the mutation could result in an extremely dangerous disease, such as cancer. In the future, the genes may be transferred within liposomes, spheres consisting of a fatty substance called lipid.
Currently, the test for the cystic fibrosis gene is 85% effective in detecting the gene in a person's blood, cheekscrapings, or saliva. Some researchers believe that this effectiveness rate is still too low and that testing should be performed only on persons who have a familial history of cystic fibrosis. Others argue that because the test is relatively inexpensive, easy to perform, and the effectiveness rate acceptable, the test should be offered to everyone. First-trimester prenatal testing for the disease has been available since 1986. Studies have shown that only a small percentage of parents take advantage of the test, and many parents who have had one child with cystic fibrosis simply have no more children.
For Further Study
Books
Shapiro, Burton L. and Ralph C. Heussner, Jr. A Parent's Guide to Cystic Fibrosis. Minneapolis: University of Minnesota Press, 1990.
Periodicals
Brock, David J.H. "Prenatal Screening for Cystic Fibrosis: 5 Years' Experience Reviewed." The Lancet 347, January 20, 1996, p. 148.
"Gene Therapy for CF Reaches Human Lungs." Science News 146, September 3, 1994, p. 149.
Jedlicka-Kohler, Ilse, Manfred Gotz, and Irmgard Eichler. "Utilization of Prenatal Diagnosis for Cystic Fibrosis over the Past Seven Years." Pediatrics 94, July 1994, p. 13.
Johnson, Larry G. "Gene Therapy for Cystic Fibrosis." Chest 107, February 1995, pp. 775-815.
Koch, Christian, and Holby Niels. "Pathogenesis of Cystic Fibrosis." The Lancet 3341, April 24, 1993, p. 1065.
Norvell, Candyce. "The Facts on Cystic Fibrosis." Current Health 21, May 2, 1995, p. 22.
Samuelson, Wayne M. "Cystic Fibrosis: A Newer Outlook." Medicine 74, January 1995, pp. 58-63.
Webb, A.K., and TJ. David. "Clinical Management of Children and Adults with Cystic Fibrosis." British Medical Journal 308, February 12, 1994, pp. 459-63.
Audiovisual Recordings
Alex: The Life of a Child. Bethesda, MD: Cystic Fibrosis Foundation, 1986 (produced by ABC-TV).
(One 95-minute video.)
CF Gene Therapy: A Medical Revolution. Bethesda, MD: Cystic Fibrosis Foundation, 1997.
(One sixteen-minute videocassette.)
The Effect of Ibuprofen on CF Lung Disease. Bethesda, MD: Cystic Fibrosis Foundation, 1995.
(One 8-minute videocassette.)
From Molecules to Miracles. Bethesda, MD: Cystic Fibrosis Foundation, 1995.
(One 56-minute videocassette.)
A Guide for Parents and Children. Bethesda, MD: Cystic Fibrosis Foundation/McNeil Pharmaceutical, 1988.
(One 38-minute videocassette.)
Solving the CFTR Protein Puzzle. Bethesda, MD: Cystic Fibrosis Foundation, 1996.
(One 14-minute videocassette.)
Organizations
Cystic Fibrosis Foundation
Address: 6931 Arlington Rd.
Bethesda, MD 20814
Telephone: toll-free (800) FIGHT-CF; (301) 951-4422
e-mail: infor@cff.org
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