Cystic Fibrosis (CFTR) Gene Analysis

What is cystic fibrosis (CFTR) gene analysis?

Cystic fibrosis is an inherited disease that causes the body's secretions to thicken. It mainly affects the lungs and the digestive system; it can lead to recurrent lung infections, insufficient secretion of digestive enzymes by the pancreas and difficulty gaining weight. The disease results from changes in the gene that encodes the CFTR protein, which regulates the movement of salt and water across the cell membrane.

Cystic fibrosis is inherited in an autosomal recessive manner: for the disease to occur, a disease-associated variant must be present in both copies of the gene. People who carry a variant in one copy are carriers and usually show no symptoms. In CFTR gene analysis, all coding regions of the gene are sequenced in DNA extracted from blood. Because different variants can be seen in different populations, examining the whole gene provides more comprehensive information than tests that look only at common variants; an additional method may be needed for large deletions.

When is CFTR gene analysis ordered?

A cystic fibrosis diagnosis is made with the sweat test together with clinical findings; genetic analysis is used to support the diagnosis, identify the disease-causing variants and allow family members to be assessed. Your doctor may order this test both for people with symptoms and for people at risk of being carriers.

• A high or borderline sweat test result
• Suspected cystic fibrosis on newborn screening
• Recurrent lung infections, chronic cough or bronchiectasis
• Pancreatic insufficiency, fatty stools or difficulty gaining weight
• Congenital absence of the sperm ducts in male infertility
• A cystic fibrosis diagnosis or known carrier status in the family
• People who are planning to have children, are in a consanguineous marriage or whose partner is a carrier

Carrier testing helps assess the likelihood that people without symptoms could pass this disease on to their children. If both partners are carriers, the options for future pregnancies are discussed in detail in genetic counseling.

How do you prepare for CFTR gene analysis?

No fasting is needed for this test, and the blood sample can be given at any time of day. The medications or respiratory treatments you use do not affect the genetic result. If you are having the test to check carrier status and cystic fibrosis has previously been diagnosed or genetic testing done in your family, sharing these reports with your doctor helps the result be interpreted correctly.

Genetic tests are performed with informed consent, and genetic counseling is recommended, especially for carrier tests. If you have had a bone marrow transplant, mention this. The test is performed on the person's own blood sample; prenatal diagnosis of the baby during pregnancy requires different samples and methods. Our nurse collects your blood sample at your home or workplace.

How are CFTR gene analysis results interpreted?

The report states the variants found, their association with the disease and whether they are present in one or both copies of the gene. Finding disease-causing variants in both copies supports a cystic fibrosis diagnosis in a person with compatible clinical findings and sweat test results. A variant in a single copy, on the other hand, usually means carrier status. Some variants may be associated with milder forms or with involvement of a single organ only, such as male infertility.

Not finding a variant markedly reduces the likelihood of carrier status; however, because of rare changes that the test cannot detect, it does not eliminate this possibility entirely. When a variant of uncertain significance is found, the result is not used on its own for decisions. Your result should be evaluated together with your symptoms, sweat test and family history by your doctor and, if needed, a medical geneticist.