Genetic Disease Profile: Cystic Fibrosis

For more about the gene that causes cystic fibrosis, see the CFTR Gene Profile. The following was taken from NIH Publication No. 95-3650.

Disease Description

Cystic fibrosis (CF) is a chronic, progressive, and frequently fatal genetic (inherited) disease of the body's mucus glands. CF primarily affects the respiratory and digestive systems in children and young adults. Sweat glands and the reproductive system also are usually involved. On average, individuals with CF have a lifespan of about 30 years.


Inheritance

CF is an autosomal recessive disorder caused by mutations in the CFTR (cystic fibrosis transmembrane conductance regulator) gene. Heterozygous carriers (those who have inherited only one copy of the altered gene) are asymptomatic. Two altered genes must be present for CF to appear. This means that if both parents are CF carriers, their offspring would only express CF symptoms if they had inherited one defective copy of the CFTR gene from each parent.


Incidence

According to data collected by the Cystic Fibrosis Foundation, about 30,000 Americans, 3000 Canadians, and 20,000 Europeans have CF. The disease occurs mostly in whites whose ancestors came from northern Europe, although it affects all races and ethnic groups. Accordingly, it is less common in African Americans, Native Americans, and Asian Americans. About 2500 babies are born with CF each year in the United States. Also, about 1 in every 20 Americans is an unaffected carrier of an abnormal CF gene. These 12 million people usually are unaware that they are carriers.


Symptoms

CF does not follow the same pattern in all patients but affects different people in different ways and to varying degrees. The basic problem, however, is the same—an abnormality in the glands that produce or secrete sweat and mucus. Sweat cools the body; mucus lubricates the respiratory, digestive, and reproductive systems and prevents tissues from drying out, protecting them from infection.

Loss of excessive amounts of salt in sweat can upset the balance of minerals in the blood, which may cause abnormal heart rhythms. Shock also is a risk.

Thick accumulations of mucus in the intestines and lungs result in malnutrition, poor growth, frequent respiratory infections, breathing difficulties, and eventually permanent lung damage. Lung disease is the cause of death in most patients.

Various other medical problems may include inflammation of the nasal sinuses, nasal polyps, clubbing of fingers and toes, pneumothorax (rupture of lung tissue and trapping of air between the lung and chest wall), coughing of blood, heart enlargement, abdominal pain and discomfort, gassiness, and rectal prolapse. Liver disease, diabetes, pancreatic inflammation, and gallstones also occur in some people with CF.


Diagnosis and Genetic Testing

Sweat test is the most common test for CF. It measures the amount of salt (sodium chloride) in the sweat.

Immunoreactive Trypsinogen Test (IRT) is used for newborns who do not produce enough sweat for the sweat test. In the IRT test, blood drawn 2 to 3 days after birth is analyzed for a specific protein called trypsinogen. Positive IRT tests must be confirmed by sweat and other tests.

Other tests that can assist in the diagnosis of CF include chest X rays, lung function tests, sputum (phlegm) cultures, and stool examinations to help identify typical digestive abnormalities.

Molecular Genetic Testing involves carrier screening and direct DNA analysis. Current tests, however, cannot detect all of the more than 900 gene mutations, and so the tests are only 80% to 85% accurate [1].


Treatment

CF once was always fatal in childhood. Better treatment methods developed over the past 20 years have increased the average lifespan of CF patients. At present, neither gene therapy nor any other kind of treatment exists for the basic causes of CF, although several drug-based approaches are being investigated. In the meantime, doctors can only ease the symptoms of CF or slow the progress of the disease so the patient's quality of life is improved. This is achieved by antibiotic therapy combined with treatments to clear the thick mucus from the lungs. The therapy is tailored to the needs of each patient. For patients whose disease is very advanced, lung transplantation may be an option.

References

1. Tait, Jonathan F., et al. (Updated 12 April 2001). Cystic Fibrosis. In: GeneReviews at GeneTests·GeneClinics: Medical Genetics Information Resource [database online]. Copyright, University of Washington, Seattle. 1997-2001. Available at http://www.geneclinics.org or http://www.genetests.org. Accessed 20 May 2002.

Organizations and Support Groups

Cystic Fibrosis Foundation

Cystic Fibrosis Research, Inc.

Canadian Cystic Fibrosis Foundation

Cystic Fibrosis World Wide

Cystic-L Cystic Fibrosis Information and Support

Diagnostic Testing

Cystic Fibrosis Testing - From GeneCare Medical Genetics Center

Cystic Fibrosis Carrier Testing: A Guide for Parents - Publication created by the Michigan State University DNA Diagnostic Program

Cystic Fibrosis Research Directions - NIH Publication 97-4200

Ask NOAH About: Cystic Fibrosis - Links to CF resources by New York Online Access to Health (NOAH)

Clinical Trials

Cystic Fibrosis Studies - Listed at clinicaltrials.gov

Clinical Trials Information - From the Cystic Fibrosis Foundation

International Cystic Fibrosis Clinical Trials Registry - From the Cystic Fibrosis Foundation

Other Cystic Fibrosis Resources

MedlinePlus Entry for Cystic Fibrosis

NCBI Genes and Disease Entry for Cystic Fibrosis

Johns Hopkins Medicine: Cystic Fibrosis

Last updated: November 27, 2002