Cystic fibrosis

Cystic fibrosis (CF) is an inherited disease caused by a change (mutation) in the CF gene. It is a chronic, progressive disease that causes mucus to become thick, dry, 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 malnutrition, which can lead to problems with growth and development.

CF is usually diagnosed during childhood. While life expectancy for someone with CF is about 32 years, new treatments are improving symptom control and increasing life expectancy.

What Is the Cause?

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; however, there is a 50 percent chance that the child will be a CF carrier.
  • If both parents are carriers, there is only a 25 percent chance that the child will have CF, but a 50 percent 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 the 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 a health professional must order it. Genetic counseling to help you understand the meaning and possible results of the test is recommended prior to genetic testing.

The National Institutes of Health recommend CF carrier screening for:

  • Adults with a positive family history of CF.
  • Partners of people with CF. If one partner has CF and the other partner had the defective CF gene, a child will have a 50 percent 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 your child will have CF.

  • If you and your partner are both carriers of CF there is a 1 in 4 (25 percent) chance that your child will have a child with CF.
  • 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?

Screening determines whether a person is a carrier of CF about 90 percent of the time. There is a small risk that you may be a CF carrier even when the test results are negative.

Why Should I Be Screened?

The decision to have 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 especially likely if either of you have a family member with the disease.

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; it is much less common in other racial and ethnic groups.

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

You may decide to have carrier testing for CF if you are already pregnant and the test results will affect your decision to continue your pregnancy or help 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 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.
  • Carrier testing is expensive. You may decide not to have testing if your insurance does not pay for it.
  • Testing is not 100 percent accurate. There is a small chance that you are carrier even if the results are normal (negative).