What is Genetic Testing for Cystic Fibrosis
Cystic fibrosis (CF) is a disease that affects many different parts of the body. It is often considered a lung disease, and breathing (respiratory) failure is the most serious problem related to the condition. But CF can also affect other parts of the body, including the skin, pancreas, liver, intestines, sinuses, sweat glands, and sex organs.
Cystic fibrosis is caused by an abnormal (mutated) gene that is passed from parent to child (inherited). This gene causes the body’s secretions to thicken. When mucus in the lungs becomes thick and very sticky, this causes difficulty breathing and frequent lung infections. It is possible to check for genes that can cause CF by looking at cell chromosomes (genetic testing).
How is cystic fibrosis inherited?
The CF gene is called cystic fibrosis transmembrane conductance regulator (CFTR). It is possible to have the CFTR gene without developing the disease. To develop CF, you must inherit two copies of the mutated CFTR gene, one from each parent.
Most parents of children with CF do not have CF because each parent has only one CFTR mutation. When a person can pass along the CFTR gene, but the person does not have CF, this person is called a CF carrier.
- If both parents are CF carriers, each child has a one in four chance of having CF.
- If a mother has CF and a father is a carrier, each child has a one in two chance of having CF.
- If neither parent has the CFTR gene mutation, no child will have CF.
Who should be tested?
- All women should be offered genetic testing for CF during childbearing years. Testing may be done before or during pregnancy.
- If a woman tests positive and is a CF carrier, her male partner who is or may become the father of her child should be tested.
- If a man and a woman are both CF carriers and the woman is or becomes pregnant, the baby in her womb should be tested for CF (prenatal testing).
- In the U.S., all newborns are tested for CF.
- Any child or adult with CF symptoms or a family history of CF may be tested.
- Relatives of people who test positive as CF carriers or who are diagnosed with CF may choose to be tested.
How is genetic testing done?
Many possible mutations can affect the CFTR gene. Genetic testing checks for the 24 most common ones (CF gene mutation panel). There is no preparation needed for this test. The way the test is done depends on who is being tested:
- Adults and older children may have blood drawn from an arm, or may have a cheek swab done.
- Newborns are tested using a blood sample from a heel prick.
- Prenatal
testing is done by taking a fluid sample from inside the womb (amniocentesis)
or a sample of cells from the placenta (chorionic villus sampling).
- Amniocentesis can be done after 15 weeks of pregnancy.
- Chorionic villus sampling can be done between 10 and 13 weeks of pregnancy.
What do the results mean?
A negative test means that it is highly unlikely you have a CFTR mutation. A positive test means that you have a genetic mutation on the CFTR gene. These are the possible results:
- If you are positive for two copies of the mutation, you may be diagnosed with CF.
- If you are positive for one copy of the mutation, you may be a carrier. Your siblings and your male partner should be tested.
- If you and your partner test positive as carriers, any child you have will be at risk for CF. If you are pregnant, consider prenatal testing for CF.
- If you test negative for CF, but you have CF symptoms, you may need more tests to check for less common mutations.
If you test positive for a CF mutation, you should work with a health care provider who specializes in counseling for genetic disorders (genetic counselor). Genetic counseling is most important for couples who are CF carriers and want to have children.
- If
you are pregnant and both you and your partner are carriers, genetic
counseling may include information about:
- Having your baby tested before birth with amniocentesis or chorionic villus sampling.
- Continuing the pregnancy and learning how to prepare for a child with CF.
- Deciding to end the pregnancy if your baby tests positive for CF.
- If
you and your partner are carriers and you are not pregnant, genetic
counseling may include information about:
- Considering options like adoption.
- Having prenatal testing with each pregnancy.
- Having in vitro fertilization (IVF). With IVF, fertilization takes place outside the body. The fertilized egg (embryo) can be tested for CF (preimplantation genetic diagnosis). If the embryo is negative for CF, it can be placed into your womb to grow.
Where to find more information
- Cystic Fibrosis Foundation: cff.org
- American College of Obstetricians and Gynecologists: acog.org
- American Association for Clinical Chemistry: labtestsonline.org
Summary
- Cystic fibrosis is caused by an abnormal (mutated) gene that is passed from parent to child (inherited).
- To develop CF, you must inherit two copies of the mutated CFTR gene, one from each parent.
- People who carry one copy of the mutation are called CF carriers.
- CF carrier testing is recommended for all women of childbearing age, before or during pregnancy.
- If both you and your partner are CF carriers, a genetic counselor can provide information about options for becoming parents.
