It is estimated that in the United States, more than 30,000 people have cystic fibrosis, and more than 10 million people carry the CF trait. A carrier does not have the disease or any of the symptoms, but is capable of passing CF on to his or her children.
Genetic testing for cystic fibrosis is done to determine if a person has, or is a carrier of, cystic fibrosis. The test is usually done on a blood sample, but sometimes can be done on other DNA-containing cells such as a swab from the inside of the cheek. The sample is examined for a specific panel of mutations of the CFTR gene. Everyone has two copies of the CFTR gene in every one of their cells. If one copy, also known as an allele, is found to have a mutation, the person is a carrier. If both copies of the gene are mutated, the person has cystic fibrosis disease.
There are more than 1,500 different CFTR mutations known to cause CF, and new mutations are being discovered as research on the gene continues. No test checks for all of the possible CF-causing mutations, but several tests are available that check for the most common CFTR mutations. The cost of genetic testing ranges from a few hundred to several thousand dollars, and may or may not be covered by insurance.
Basic Test – ACMG/ACOG Mutation Panel
The basic genetic test for cystic fibrosis, sometimes referred to as the ACMG/ACOG Mutation Panel or the 23-mutation panel, looks for the most commonly occurring CFTR mutations. It is about 90% effective in detecting CF mutations in the Caucasian population, but only about 70% effective in African-Americans and 60% effective in the Hispanic population.
The test is widely available at local and regional labs, but the specific mutations tested for will vary according to lab protocols. Some labs check for more, but the basic test should at least include the 23 mutations recommended by the American College of Medical Genetics (ACMG) and the American College of Obstetricians and Gynecologists (ACOG). Results are usually available within a few days, but may take longer if the specimen must be sent to a larger lab for testing.
Some companies have developed tests that can identify less common mutations in addition to those in the ACMG/ACOG recommended panel. These tests can be especially helpful in detecting rare CF mutations when done as follow-up tests if the basic panel produced normal results. Some people opt to have this more thorough testing for their initial test, especially if they are likely to have a less common CFTR mutation. The advanced tests are highly specialized and must be sent to the labs that offer them. They may cost more and take longer to receive results than the basic testing panel done at a local lab.
American College of Medical Genetics “Cystic Fibrosis Population Carrier Screening: 2004 Revision of American College of Medical Genetics Mutation Panel”. 2004. Genet Med 6:5, 387-391. 11 July 2008.