A person who is a cystic fibrosis carrier has one copy of the gene for the condition. People need to have two copies of the gene to have cystic fibrosis.
If a cystic fibrosis (CF) carrier has a child with another CF carrier, there is a chance that the child may also be a carrier or that they might have the disease.
Research suggests that as many as 10 million people in the United States are CF carriers. Testing can help an individual discover whether they are among these individuals.
Read on to learn more about cystic fibrosis carriers.
CF carriers do not experience any symptoms. As a result, most people who are carriers remain unaware that they have the CF gene.
A person may only find this out if they receive a positive result from a carrier test or have a child with CF.
If a person with CF has a child with a CF carrier, the child will either have CF or be a carrier of the disease.
People with CF may have the following signs and symptoms:
- chronic lung infections
- a persistent cough
- chronic or frequent sinusitis
- digestive issues, including bulky, greasy stools and constipation
- nasal polyps, which are fleshy growths in the nose
- salty-tasting skin
- poor growth
- nutritional deficiencies
- liver disease
The symptoms of CF vary in type and severity. Some mutations of the CF gene lead to more severe symptoms than others. To date, scientists have discovered more than 1,700 mutations that can cause CF.
People who have a family history of CF may wish to get a CF carrier test before starting a family.
The American College of Obstetricians and Gynecologists recommend that doctors offer carrier screening to any woman who is pregnant or considering becoming pregnant.
Often, doctors will first offer a test to the woman who wants to become pregnant. The procedure involves a simple blood test.
Depending on the specific type of blood test that the doctor orders, it may also test for the presence of other genetic disorders.
The type and number of conditions that the individual wishes to check for will determine the cost of genetic testing, which can vary greatly. A doctor can usually advise people on their options and the cost of each.
If the woman receives a negative carrier test result, it is unlikely that she will have a child with CF. However, it is still a possibility as the test cannot detect all of the possible mutations of the CF gene, especially the rarer ones.
If the woman receives a positive result, it means that she is almost definitely a carrier of the CF gene. A positive result is more than 99% accurate. In this case, her partner may wish to request a test to check whether they are also a carrier.
If both members of a couple are carriers, they could consider meeting with a genetic counselor before getting pregnant to discuss their options.
During pregnancy, a doctor may test both partners together due to time constraints. If both parents are CF carriers, they may wish to consider prenatal testing to determine whether the fetus has inherited two copies of the defective gene.
Prenatal testing can identify whether a child has CF, but it cannot predict the severity of the symptoms. The prenatal CF tests are:
- Amniocentesis. Between weeks 15 and 20 of pregnancy, a doctor can remove a sample of amniotic fluid and send it to a laboratory for analysis.
- Chorionic villus sampling (CVS). This test involves taking a sample of tissue from the placenta. Doctors can do CVS between weeks 10 and 13 of pregnancy.
A genetic counselor can provide information and support to couples who discover that their unborn child has tested positive for CF.
Newborn screening tests in all 50 U.S. states now check for CF. These tests can determine whether a baby is likely to have CF or, sometimes, if they are a CF carrier.
Screening other family members
If parents have a child with CF or a child who is a CF carrier, all of their other children should undergo a screening test, even if they do not have symptoms.
These children and other blood relatives are at higher risk of being carriers of the CF gene mutation.
CF is a relatively common disease, affecting more than 30,000 people in the U.S. An additional 10 million people are CF carriers.
The likelihood of carrying the faulty CF gene varies by ethnicity:
- White European and Ashkenazi Jews — 1 in 29
- Hispanic Americans — 1 in 46
- African Americans — 1 in 61
- Asian Americans — 1 in 90
People with a family history of CF have a higher chance of being a carrier. If both parents are CF carriers, their children have:
- a 25% chance of having CF
- a 50% chance of being a carrier
- a 25% chance of not having CF and not being a carrier
Children with the same parents all have an equal chance of inheriting the CF mutation, regardless of whether their siblings are CF carriers or have CF symptoms.
If a carrier has a child with someone with CF, the child will either have CF or be a CF carrier.
People who are planning to have children may wish to speak to a doctor about CF carrier screening, especially if they have a relative with CF.
It is possible to undergo screening before or during pregnancy. All babies born in the U.S. receive screening for CF at birth.
It can also be helpful to discuss these tests with a genetic counselor to understand how the results may affect each individual, the couple, and their children.