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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If you are a cystic fibrosis (CF) carrier, it means that you carry the trait in your genes, and could pass cystic fibrosis along to your child. Carrying the gene does not mean you have cystic fibrosis.

Typically, every person has 23 pairs of chromosomes. 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.

Your Chances of Passing CF on to Your Child

Cystic fibrosis occurs when both copies of the CFTR gene contain a mutation. If you and your partner are both CF carriers, you could pass CF on to your child. 

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 they inherit a mutated chromosome from one of you and a normal one from the other, they will be a CF carrier. If your child inherits the normal chromosome from both of you, he will have two normal copies meaning he neither carries nor has CF.

The possible combinations that two CF carriers can pass onto 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, your child will have a 25 percent chance of being a carrier, which would occur if they received the mutated CFTR gene from you. Meaning they could pass it on to their children.

    Your Health as a CF Carrier

    If you are a CF carrier, you do not have to worry about developing cystic fibrosis. You will not develop the disease because you have one normal CFTR gene. Being a CF carrier will not cause you to be ill or require you to seek treatment. Nor will being a CF carrier shorten your life 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.

    Sources:

    Boyle, MP, MD. “Adult Cystic Fibrosis.” Journal of the American Medical Association. 2007 298:1787-1793. 17 June 2008.

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

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