What Does It Mean to Be a Cystic Fibrosis Carrier?

Having the CF Gene Does Not Mean You Have Cystic Fibrosis

Genetic code
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Cystic fibrosis is an inherited disease that causes lung and sinus infections, failure to thrive as an infant and digestive problems like oily, stools from fat malabsorption in the gut or severe constipation.

Let's explore the inheritance pattern of cystic fibrosis, as well as the statistical chances of a child developing CF if both parents are CF carriers.

Cystic Fibrosis: Autosomal Recessive Disease

Every person has 23 pairs of chromosomes in each cell.

Of those 23 pairs, one pair is the sex chromosomes (the X chromosome and Y chromosome) and the other 22 pairs of chromosomes are called autosomes.

Each chromosome pair contains the same genes, but not necessarily the same gene code. For instance, both chromosomes in the pair that determines hair color will contain a color gene, but one may be brown and the other one blonde.

Cystic fibrosis is caused by a mutation of the cystic fibrosis transmembrane regulator (CFTR) gene. If you are a CF carrier, it means that one of your CFTR genes is normal, and the other contains a mutation that is known to cause cystic fibrosis.

Cystic fibrosis only occurs when both copies of the CFTR gene contain a mutation—this is why cystic fibrosis is called an autosomal recessive disease, as opposed to an autosomal dominant disease (in which only one copy of the mutated gene is needed for disease development).

The clincher is if you and your partner are both CF carriers, you could pass CF on to your child.

This is because your child will inherit one chromosome of each pair from you, and one from your partner. If your child gets both copies of the chromosome containing the mutated CFTR gene, they will have two mutated copies and will be born with cystic fibrosis.

If your child inherits a mutated chromosome from one of you and a normal one from the other, they will be a CF carrier, but not have cystic fibrosis.

If your child inherits the normal chromosome from both of you, he will have two normal copies, meaning he neither carries nor has CF.

Cystic Fibrosis: Statistical Possibilities

Here is another way to look at what it means to be a CF carrier.

The possible combinations that two CF carriers can pass on to their child are:

  • Normal CFTR from mom + mutation from dad = carrier
  • Normal CFTR from dad + mutation from mom = carrier
  • Normal CFTR from mom + normal CFTR from dad = not a carrier and does not have CF
  • Mutated CFTR from mom + mutated CFTR from dad = cystic fibrosis

If you and your partner are both carriers, your child has a 25 percent chance of having CF, a 50 percent chance of being a carrier, and a 25 percent chance of neither having nor carrying CF.

If your partner is not a CF carrier, it will be impossible for your child to have CF because he can only inherit normal copies of the CFTR gene from your partner. However, if your child received the mutated CFTR gene from you, he or she will have a 25 percent chance of being a carrier. In this case, your child could then pass on the CF trait to their children.

What It Means to Be a Health Carrier

If you are a CF carrier, you will have no symptoms of cystic fibrosis and do not have to worry about developing the disease.

In addition, being a CF carrier will not shorten your lifespan or limit you in any way (with the exception of family planning).

When you do start thinking about having children, you and your partner should seek genetic counseling to determine your combined risk of passing CF on to your future children. More specifically, you can see if you and your partner are CF carriers by undergoing a blood test to check for the CF gene.

A Word From Verywell

A final tidbit to know is that prior to newborn screening programs, the majority of people did not find out they had CF until they had symptoms. Now, if an infant has a positive CF newborn screening test, he or she will undergo a sweat chloride test to confirm the diagnosis of CF.

With a sweat chloride test, the salt content of the baby's sweat is measured. People with CF have an abnormally high level of salt in their sweat because of impaired sweat gland function. 

With an earlier diagnosis, care under a special CF medical team can be initiated sooner. This team often includes doctors (especially a lung doctor with expertise in CF), nurses, a dietician, a respiratory therapist, a physical therapist, psychologist, and a social worker.

Sources:

Torpy JM, Lynm C, Glass RM. Cystic fibrosis. JAMA Patient Page. JAMA. 2009;302(10):1130.

University of Virginia Health System. (2016). Cystic Fibrosis.

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