Carrying the CF Trait in Your Genes
Each of us 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 (CF) 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 disease 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. Here’s how it works.
Your child will inherit one chromosome of each pair from you, and one from your partner. If your child gets the chromosome containing the mutated CFTR gene from both of you, he will have two mutated copies. Thus, he will have CF. If he inherits a mutated chromosome from one of you and a normal one from the other, he 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 = Has cystic fibrosis
Broken down into odds, if the parents are both carriers, your child has a 25% chance of having CF, a 50% chance of being a carrier, and a 25% 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% chance of being a carrier, which would occur if he received the mutated CFTR gene from you. Meaning he could pass it on to his children.
If You Are a Carrier, You Do Not Have CF
If you are a CF carrier, you do not have to worry that it will someday turn into CF disease. This can never happen because you have one normal CFTR gene. Being a CF carrier will not cause you to be ill or require you to seek treatment. It will not shorten your life or limit you in any way except for making decisions about child bearing. When you do start to think about having children, you and your partner should seek genetic counseling to find out what your risks as a couple are of passing CF on to your future children.
Sources: The Genetics of Cystic Fibrosis. University of Virginia Health System. November 7, 2005. http://www.healthsystem.virginia.edu/uvahealth/peds_respire/cfgenetc.cfm
Boyle, MP, MD. “Adult Cystic Fibrosis.” Journal of the American Medical Association. 2007 298:1787-1793. 17 June 2008.
The Genetics of Cystic Fibrosis. University of Virginia Health System. November 7, 2005. http://www.healthsystem.virginia.edu/uvahealth/peds_respire/cfgenetc.cfm