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Q. What are the chances of a person with cystic fibrosis passing the disease to their offspring?

A: Cystic fibrosis is inherited as a recessive disease. This means a person could be a carrier of a CF mutation and not be affected.

Everyone has two copies of the CF gene. You get one from your mother and one from your father. CF happens when both copies of the inherited cystic fibrosis transmembrane receptor (CFTR) gene are mutated or altered.

Every child born to a person who has cystic fibrosis will inherit one CFTR gene mutation from that affected parent. So, all the children would be at least a carrier for CF.

The chance that a child born to a person with cystic fibrosis will actually have the disease depends on whether that person’s partner is a carrier of a CFTR gene mutation or not. The chances of being a carrier would be higher if the partner has a family history of cystic fibrosis.

But even without a family history, some ethnic groups have a pretty high risk of being a carrier. In some cases, it’s about a 1-in-25 chance. Also, there is no way to rule out being a carrier just by knowing the partner’s ethnicity.

The best approach for a couple concerned about having a child with cystic fibrosis is to first speak with their primary care doctor. He or she can make a referral to a clinical geneticist or genetic counselor to discuss options for carrier testing. There are different types of tests to look for CFTR mutations. The right test depends on the couple’s particular situation.

Dr. David T. Miller is a clinical geneticist at Boston Children’s Hospital.