What Is Cystic Fibrosis?
Cystic fibrosis (CF) is an inherited disease caused by a change (mutation) in the cystic fibrosis transmembrane regulator (CFTR) gene. It is a chronic, progressive disease that causes mucus to become thick and sticky. The mucus builds up and clogs passages in many of the body's organs, but mostly in the lungs and the pancreas. In the lungs, the mucus can cause serious breathing problems and lung disease. In the pancreas, the mucus can cause digestive problems and malnutrition, which can lead to problems with growth and development.
What Causes CF?
Cystic fibrosis (CF) is a genetic disorder. A child must inherit two defective CF genes (one defective gene from each parent) to have the disease.
A person who has inherited only one defective CF gene is a carrier of CF and does not have the disease but can pass it on to his or her children. This person can also pass on carrier status.
- If only one parent is a carrier of a defective CF gene, the child will not have CF. But there is a 50% (1-in-2) chance that the child will be a CF carrier.
- If both parents are carriers, there is a 25% (1-in-4) chance that the child will have CF, and a 50% chance that the child will be a carrier.
What Is Carrier Screening?
Cystic fibrosis (CF) carrier screening is a blood test that determines if you are a carrier of one of the defective genes that causes CF. The test can help you determine if you and your partner have an increased chance of having a child born with CF.
Who Should Be Screened?
Genetic testing can help people find out if they may be carriers of cystic fibrosis (CF). This type of genetic testing allows parents to find out if they have an increased chance of having a child with CF. Anyone who is interested in knowing his or her carrier status can request the test, but the test can only be ordered by a doctor. Genetic counselling to help you understand the meaning and possible results of the test is recommended prior to genetic testing.
Cystic Fibrosis Canada recommends carrier screening for family planning purposes for:footnote 1
- People who have a family history of CF.
- People with a partner who has a family history of CF.
- People who have a medical condition that might be related to CF, such as male infertility.
If you are pregnant and have not had CF carrier screening, the Society of Obstetricians and Gynaecologists of Canada (SOGC) recommends testing for:footnote 2
- People who have a positive family history of CF.
- People who have symptoms of CF.
The SOGC does not recommend routine screening of all women.
If the test shows that you are a carrier of cystic fibrosis (CF), your partner should also be tested.
If you had this screening test before, do not get tested again. Give your past results to your doctor.
What If I Am a Carrier?
Both parents must be carriers of CF for a child to have the disease. If tests show that you are a carrier but your partner is not a carrier of a CF gene, there is a very small chance that you will have a child with CF.
If you and your partner are both carriers of CF, there is a 1-in-4 (25%) chance that your child will have CF.
Is Screening Accurate?
This test does a good job of detecting whether a person is a carrier of the most common changed genes that can cause CF. The test is most accurate in Ashkenazi Jews and white people.footnote 3 This is partly because CF occurs most commonly in people of these ethnic groups. As with all tests, there is a small risk that you may be a CF carrier even when the test results show that you are not a carrier.
Should I Be Screened?
The decision to have cystic fibrosis (CF) carrier screening is a personal one. You may wish to be tested if you are concerned that you or your partner might be carriers of CF. This may be more likely if either of you has a family member with the disease.
Some people decide to be tested to help find out their risks of passing on to their children a disease that shortens life. Among whites, about 2 to 5 out of 100 are carriers of a defective CF gene.footnote 4 CF is much less common in other racial and ethnic groups.
You may decide to have carrier testing for CF if you are already pregnant. The test results may influence your decision about your pregnancy or help you make decisions about the care of your newborn child.
Why Not Be Screened?
There may be reasons you would choose not to have cystic fibrosis (CF) carrier testing.
- You think that your risk of being a carrier is low. This may be true if you are an African American or an Asian American. The incidence of CF is lower in these groups.
- You are already pregnant and the information obtained from testing will not affect your decision to continue your pregnancy. Remember, though, that CF test results can provide valuable information for the care of your unborn child.
- Carrier testing is expensive. You may decide not to have testing if your health plan does not pay for it.
- Testing does not identify all people who have a mutation in the CF gene. There is a small chance that you are a carrier even if the results are normal (negative).
- Cystic Fibrosis Canada (2011). Carrier testing for cystic fibrosis. Available online: http://www.cysticfibrosis.ca/assets/files/pdf/Carrier_Testing_for_cystic_fibrosisE.pdf.
- Wilson RD, et al. (2002). Cystic fibrosis carrier testing in pregnancy in Canada. SOGC Committee Opinion No. 118. Journal of Obstetrics and Gynaecology Canada, 24(8): 644–647.
- Egan M (2011). Cystic fibrosis. In RM Kliegman et al., eds., Nelson Textbook of Pediatrics, 19th ed., pp. 1481–1497. Philadelphia: Saunders.
- Boucher RC, et al. (2010). Cystic fibrosis. In R Mason et al., eds., Murray and Nadel's Textbook of Respiratory Medicine, 5th ed., vol. 1, pp. 985–1022. Philadelphia: Saunders.
Current as ofDecember 12, 2018
Author: Healthwise Staff
Medical Review: John Pope, MD, MPH - Pediatrics
Brian O'Brien, MD, FRCPC - Internal Medicine
Kathleen Romito, MD - Family Medicine
Susanna A. McColley, MD - Pediatric Pulmonology
R. Steven Tharratt, MD, FACP, FCCP - Pulmonology, Critical Care Medicine
Current as of: December 12, 2018