Cystic Fibrosis Carrier Screening

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 primarily 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.

Cystic fibrosis is usually diagnosed during childhood. On average, people who have cystic fibrosis live into their mid-to-late 30s, although new treatments are making it possible for some people to live into their 40s and longer.

What Causes Cystic Fibrosis?

Cystic fibrosis 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 cystic fibrosis 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, but a 50% chance that the child will be a carrier.

What Is Carrier Screening?

Cystic fibrosis carrier screening is a blood test that determines whether you are a carrier of the defective gene that causes cystic fibrosis. The test can help you determine whether you and your partner have an increased chance of having a child born with CF.

Who Should Be Screened?

Genetic testing is available to screen people who want to determine whether they may be carriers of 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 be ordered only by a health professional. Genetic counseling to help you understand the meaning and possible results of the test is recommended prior to genetic testing.

CF carrier screening is recommended for:^{1, 2}

• Adults with a positive family history of CF.
• Partners of people with CF. If one partner has CF and the other partner has the defective CF gene, a child will have a 50% chance of having CF.
• Couples planning to have children.
• Pregnant women (and their partners) who seek prenatal care, regardless of family history.

What If I Am a Carrier?

If tests show that you are a carrier of CF, your partner should also be tested. Both parents must be carriers of CF for a child to have the disease. If tests show that your partner is not a carrier of the 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.³

• If you are not already pregnant, you may wish to have genetic counseling to understand your risks and options if you decide to have children.
• If you are already pregnant, you may wish to have further testing (amniocentesis or chorionic villus sampling) to determine whether your baby has CF.

Is Screening Accurate?

The blood test can detect whether a person is a carrier of CF in about 90 out of 100 CF carriers. This rate is not the same among all racial and ethnic groups. There is a small risk that you may be a CF carrier even when the test results are negative.⁴

Should I Be Screened?

The decision to have cystic fibrosis 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 have a family member with the disease. ³

Some people decide to be tested to help determine their risks if they choose to have children. Among whites, about 1 in 29 is a carrier of a defective CF gene. CF is much less common in other racial and ethnic groups.⁴

Carrier testing is expensive. Another factor that may guide the decision to have testing is whether the cost of testing is covered by your insurance company.

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 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 insurance 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).

Other Places To Get Help

Organizations

Related Information

• Cystic Fibrosis

References

Citations

1. Genetic Testing for Cystic Fibrosis. NIH Consensus Statement, vol. 15, no. 4 (1997 April 14-16).

2. American College of Obstetricians and Gynecologists (2005, reaffirmed 2007). Update on carrier screening for cystic fibrosis. ACOG Committee Opinion No. 325. Obstetrics and Gynecology, 106(6): 1465-1468.

3. American College of Obstetricians and Gynecologists and American College of Medical Genetics (2001). Preconception and Prenatal Carrier Screening for Cystic Fibrosis: Clinical and Laboratory Guidelines. Washington, DC: American College of Obstetricians and Gynecologists.

4. Stephens K, et al. (2001). Molecular genetic testing: Cystic fibrosis DNA detection. In DS Jacobs et al., eds., Jacobs and DeMott Laboratory Test Handbook, pp. 701-718. Hudson, OH: Lexi-Comp.

Other Works Consulted

• Boat TF (2004). Cystic fibrosis. In RE Behrman et al., eds., Nelson Textbook of Pediatrics, 17th ed., pp. 1437-1450. Philadelphia: Saunders.

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