Cystic Fibrosis Inheritance: What You Need to Know

If you or someone you know has cystic fibrosis (CF), you’ve probably heard the word “inheritance” tossed around. It can feel confusing, but the basics are pretty simple. CF is caused by changes, or mutations, in the CFTR gene. Every person has two copies of this gene—one from each parent. If both copies carry a mutation, the person develops CF. If only one copy is mutated, they become a carrier and usually feel fine.

Why It’s Called Autosomal Recessive

The term “autosomal recessive” tells you two things. First, “autosomal” means the gene lives on one of the 22 non‑sex chromosomes, so the pattern is the same for boys and girls. Second, “recessive” means two faulty copies are needed for the disease to show up. In other words, a child only gets CF when they inherit a bad copy from both mom and dad.

That also means each pregnancy has a 25% chance of producing a child with CF if both parents are carriers. There’s a 50% chance the child will be a carrier too, and a 25% chance they get two normal copies. Those odds add up fast, especially in families where the disease runs in the background.

How Families Find Out Their Risk

Knowing your carrier status can change a lot of decisions. The most common way to check is a carrier screening test. It’s a simple blood draw or cheek swab that looks for the most common CFTR mutations. In Canada, many labs offer panels that catch over 90% of the mutations that cause CF.

If both parents test positive, a genetic counselor can walk them through options. Some couples choose pre‑implantation genetic diagnosis (PGD) with IVF to pick embryos that don’t have two faulty genes. Others decide to accept the risk and plan for early testing of the baby after birth. The key is having the information before it’s needed.

Even if you’re not a carrier, you might still want to know. Some people find out they carry a mutation after a relative is diagnosed with CF. In that case, getting tested can help you understand your own family’s risk and guide future family planning.

One quick tip: if you have a family history of CF, ask your doctor for a carrier test even if you feel perfectly healthy. It’s fast, relatively cheap, and gives you peace of mind.

Bottom line: cystic fibrosis follows a clear autosomal recessive pattern. Two faulty CFTR copies = disease, one faulty copy = carrier. Genetic testing and counseling turn those numbers into real‑world choices, letting families plan with confidence.