Cystic fibrosis (CF) is a genetic disease that affects the body’s exocrine glands, causing them to secrete an excess of mucus and other secretions. Exocrine glands are responsible for secreting substances onto body surfaces both internally (such as in the lungs) and externally (such as on the skin). Examples of these secretions include sweat, tears, digestive juices, and mucus.The primary organs CF affects are the lungs and the GI tract.
Every year, 1,000 children are diagnosed with CF in the United States.
Overall, there are 30,000 Americans with CF, and an estimated 8 million people carry one copy of the defective gene that causes the disease. These carriers do not have symptoms of CF, because a person must inherit two defective gene copies, one from each parent, to develop the disease. However, each child of two CF carriers has a one in four chance of being born with CF. Genetic testing is now available to identify couples at risk for having children with CF.
What are the symptoms of cystic fibrosis?
Normal mucus forms a gel-like barrier that plays an important role in protecting the cells lining the inside surfaces of these tissues. In the lungs, mucus also transports dust and other particles out of the airways and helps to prevent infection. For patients with CF, the chemical properties of mucus become altered; instead of protecting tissues from harm, the abnormal mucus obstructs the ducts and airways, causing tissue damage.
The most characteristic symptom of CF is the excessive production of thick, sticky mucus in the airways. Several factors may contribute to this mucus abnormality. In CF, the cells lining the airways do not transport salt and water normally, so mucus and other airway secretions may be depleted of water, thus becoming abnormally thick.
There are also chemical changes in the mucus proteins. The mucus becomes so thick that it clogs the airways and provides an environment in which bacteria thrive. In response, white blood cells are recruited into the lungs to fight the infection. These white blood cells die and release their genetic material, sticky DNA, into the mucus. This DNA aggravates the already excessive stickiness of the mucus, setting up a cycle of further airway obstruction, inflammation and infection. To dislodge the mucus, CF patients cough frequently and require time-consuming daily chest and back clapping and body positioning to drain lung secretions.
Because the mucus provides an ideal breeding ground for many microorganisms, CF patients have frequent airway infections. Typically, CF patients have a pattern of low-grade, persistent infection with periodic worsening, sometimes requiring hospitalization. These infections and the inflammation that accompanies them gradually damage the lungs, causing respiratory failure, the leading cause of death among CF patients.
As in the lungs, thick secretions may also clog the pancreatic ducts and damage the pancreas. In some CF patients, this damage occurs even before birth, while in others it develops more gradually. The pancreas supplies digestive enzymes and bicarbonate to neutralize stomach acid so the enzymes can work properly in the intestines. Most CF patients have insufficient amounts of digestive enzymes for normal digestion. Pancreatic insufficiency causes foul-smelling, bulky bowel movements, malnutrition and slowed growth and development. Replacement of pancreatic enzymes, however, can alleviate these symptoms. Attention to diet and supplements of fat-soluble vitamins are also required. As the disease progresses, the cells in the pancreas that make insulin may also be damaged causing the patient to develop diabetes.
In addition to the pancreas, abnormalities are seen in other parts of the gastrointestinal tract in CF. The bile ducts in the liver may be affected, causing biliary cirrhosis in a small percentage of patients. Newborns with CF may develop a condition called meconium ileus, in which the small intestine is obstructed by a plug of meconium, the material found in the newborn gastrointestinal tract.
CF also affects the reproductive organs, causing infertility in nearly all men and some women with the disease. Men with CF are generally infertile because the tubules, called the vas deferens, that transport sperm from the testes are absent or undeveloped. Fertility may be reduced in women due to abnormal cervical mucus or to menstrual irregularity.
Salt absorption in the sweat ducts is also impaired and CF patients produce sweat with five times the normal salt concentration.
The symptoms and severity of CF vary from patient to patient. For example, not all CF patients suffer from impaired pancreatic function. The degree of lung disease also varies. Some of this variation is due to differences in the specific genetic defects, but even patients with identical mutations can experience very different severities of the disease. In fact, even siblings with the same genetic defect who share other genetic traits can have different degrees of CF.
What causes cystic fibrosis?
In 1989, the genetic defect responsible for CF was discovered. Mutations in one gene, called the cystic fibrosis transmembrane conductance regulator (CFTR), cause the body to make nonfunctional CFTR protein, which leads to the disease. About 500 different mutations have since been identified in CF patients all over the world. Scientists are studying the function of the normal and the defective CFTR proteins to understand the consequences of this defect and to develop new treatment approaches based on that knowledge.
How is cystic fibrosis diagnosed?
After analyzing a patient’s family history and symptoms and performing a physical examination, there are certain tests the doctor may order if CF is suspected.Patients can be diagnosed by newborn screening or usually by age 2.
The first test that may be ordered is a sweat test. A sweat test is a standard test in diagnosing CF. It measures the amount of salt in a patient’s perspiration. Usually two tests will be performed in order to verify a CF diagnosis. Newborn babies, however, are too small to produce enough sweat for this test, so the doctor may order a blood test called an immunoreactive trypsinogen test. Immunoreactive trypsinogen is a digestive enzyme which, if measured in high levels, will indicate CF. A genetic test can also be performed to confirm the presence of CF genes. It cannot, however, determine the severity of the symptoms.
Treating and Managing Cystic Fibrosis
Improvements in antibiotic therapy, clearance of lung secretions, nutritional support, and the increase in centers with specialized expert care have increased the average survival of patients with CF from under 5 years into their mid-30’s.
Since the identification of the CF gene, there has been a rapid increase in our understanding of the disease. However, until a cure is found, the pulmonary infection and inflammation that ultimately leads to respiratory failure and premature death remain prime targets for therapy. Continued improvement in therapy directed toward removing airway mucus and reducing infection and inflammation can preserve lung function until more definitive therapy is developed. Some of the devices and drugs that have become available for therapy include the following:
The Oscillating Device
An oscillating device, sometimes called a flutter valve is, a small, hand-held device that allows patients to loosen the mucus that clogs their airways without having to endure conventional chest- and back-clapping therapy. When patients exhale through the device, rapid air pressure fluctuates in the patients' airways. The resulting vibrations dislodge the mucus from the airway walls and promote mucus movement.
In one study, three times more mucus was cleared with an oscillating device than after the chest clapping and vibration by an experienced respiratory therapist, or by vigorous voluntary coughing. Treatment with this device does not require the assistance of another person, giving the patient more independence. Further study is still needed to determine whether the improved airway clearance delays the onset of serious lung disease.
One factor contributing to mucus "stickiness" or thickness, is the DNA released from white blood cells that die while fighting bacterial infections. A naturally occurring enzyme called DNase can cut long DNA molecules into shorter pieces and reduce their stickiness. In 1993, the Food and Drug Administration approved the use of DNase for CF treatment. The enzyme is administered as an aerosol spray and is generally well tolerated, although patients may experience temporary throat irritation or hoarseness. Treatment with DNase reduced the frequency of severe episodes of lung infection and slightly improved lung function after 24 weeks of therapy. Longer studies are needed to determine whether the small improvement in lung function seen at 24 weeks persists and whether this therapy will retard progressive loss of lung function.
Antibiotic Therapy of Bacterial Infection
Pseudomonas bacteria are a leading cause of lung infection and death among CF patients. Until recently, pseudomonas infections were treated by intravenous (through the vein) administration of antibiotics that were not available in oral form. This treatment required high antibiotic doses so that enough of the drug would reach the lung. Besides being expensive, the high doses could damage the patient’s hearing and kidney function. Recently though, aerosol forms of some antibiotics have been developed, allowing the inhaled drug to directly reach the infected lung tissue. Inhaling the medication is not only easier and less expensive to administer, but the required dosage is reduced, as is the potential for side effects.
Ibuprofen, an ingredient in many over-the-counter pain relievers, has been shown to help preserve lung function in CF. This treatment was most effective in younger patients under age 13. Ibuprofen treatment should be performed only under medical supervision because the high drug doses required must be determined individually for each patient.
Malnutrition can contribute significantly to the deterioration of CF patients' health. Although the vast majority of CF patients now take supplements of pancreatic enzymes to make up for poor pancreatic function, these supplements do not fully correct the malabsorption, and many children with CF are underweight and shorter than would be expected based on parental height.
In recent years, increased attention to caloric needs, a balanced diet, and supplements of vitamins and other nutrients have contributed to the increasing longevity and well-being of CF patients. Appropriate nutritional therapy improves the patients' growth and development, strength and exercise tolerance, and may improve resistance to bacterial infections. However, researchers do not yet know to what extent better nutrition can actually delay progression of lung disease.
It is not uncommon for CF patients, with advanced disease, to undergo double lung transplantation.
What is the prognosis for cystic fibrosis?
CF researchers from many biological and medical disciplines have made substantial progress in developing new treatments to increase CF patients' life expectancy and quality of life. Improved treatment of infection, airway clearance and nutritional therapy has already had a dramatic effect on the lives of people with CF. Parents can expect most babies born with CF to survive well into adulthood and to lead productive and fulfilling lives.
Like many other medical conditions, education about CF and local support groups can be the greatest tools for managing the disease and preventing complications. The following organizations can provide additional information about CF:
Cystic Fibrosis Foundation
6931 Arlington Road
Bethesda, Maryland 20814
(800) FIGHT CF (344-4823)
National Heart, Lung and Blood Institute
P.O. Box 30105
Bethesda, MD 208524-0105
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This information is provided by the Cleveland Clinic and is not intended to replace the medical advice of your doctor or health care provider. Please consult your health care provider for advice about a specific medical condition. This document was last reviewed on: 9/18/2012...#9358