The Genetics of Cystic Fibrosis (CF): What to Know

Medically Reviewed By Nick Villalobos, MD
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Researchers have learned a great deal about the genetics of cystic fibrosis (CF). Screening programs for newborns and genetic tests can help identify carriers or confirm a CF diagnosis. Read on to learn more about the genetics of cystic fibrosis.


A woman standing outside and holding her newborn baby
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CF is caused by genetic mutations that lead to breathing and digestive difficulties. Genetic diseases are inherited from one or both parents. In the case of CF, both parents must pass on a copy of the gene for their child to develop the condition.

The gene makes the mucus in the body thicker and stickier than usual, leading to blocked airways and interfering with digestion.

Genetic mutations

Mutations in the CFTR gene lead to CF development. This gene provides the body with instructions on producing a protein called a cystic fibrosis transmembrane conductance regulator. The protein regulates the movement of salt and fluids in the body, which helps regulate the consistency of the body’s mucus.

In people with CF, the mutations can cause the protein to stop working or keep the body from producing it at all. As a result, thickened mucus builds up in the lungs and other organs. It can often impact the pancreas, which can lead to chronic infection and inflammation.

Over time, digestive and respiratory damage can become life threatening. However, there have been significant improvements in treatment.

Learn more about treatments for CF.


CF follows an autosomal recessive pattern. This means that in order for a person to develop the condition, they must inherit copies of the CFTR gene with mutations from both parents.

If a person has only one mutated gene, they will not have CF but could be a “carrier.” This means they could pass it on to their biological children. The Cystic Fibrosis Foundation estimates that around 10 million people in the United States are CF carriers, and the American Lung Association estimates that about 30,000 people in the U.S. have CF.

Not all people who inherit two mutated CFTR genes will develop CF or be carriers, however. The chances are as follows:

  • If two people with CFTR mutations but not CF have children, the chances are:
    • 1 in 2 (50%) that the child will be a carrier but not have CF
    • 1 in 4 (25%) that they will not be a carrier or have the condition
    • 1 in 4 (25%) that the child will have CF
  • If a parent with CF has a child with a carrier, the chances are:
    • 1 in 2 (50%) that the child will have CF
    • 1 in 2 (50%) that the child will be a carrier but not have the condition

Genetic testing

Numerous mutations in the CFTR gene can cause CF or be present in carriers. Doctors may be able to identify many of them with a simple blood test or cheek swab.

You may wish to ask your physician about carrier testing if:

  • someone in your family has CF
  • you are planning to have children with someone who has CF
  • you are planning to have children with someone who may be a carrier

After obtaining a sample, the doctor will send it to a lab for DNA analysis. The results can inform you about your CFTR status if you are considering having children.

Every state in the U.S. has a program that screens newborns for the condition. The screening checks blood levels for a pancreatic chemical called immunoreactive trypsinogen (IRT).

If the levels are high, it may indicate that a baby is a carrier or has CF. It’s important to note that there can be other reasons for elevated IRT levels, such as preterm or stressful births.

Following 1–2 IRT tests that show high levels, doctors may perform a DNA analysis to look for mutations in the CFTR gene. Mutations do not necessarily mean a baby has CF, however. Diagnosing CF requires a sweat test that measures the amount of salt in the baby’s sweat.

If a baby has one CF mutation and a negative sweat test, the baby does not have CF but is a carrier. If a baby has two mutations and a positive test, they have CF.

Because CFTR gene mutations run in families, consider telling blood relatives that they may be carriers. They can choose whether to be tested or not. The tests are simple and accurate, and the resulting information could be significant when planning a family.


CF is caused by mutations in the CFTR gene, which regulates the consistency of the mucus in the body. If the gene malfunctions, the mucus becomes thick and sticky and can clog airways and parts of the digestive tract. Over time, this affects the ability to breathe and get sufficient nutrients from food.

Both parents must have a CFTR mutation for a child to be born with CF. If only one parent has a mutated gene, the child may be a carrier. This means they could pass it down to their biological children later in life, but they do not have CF.

A simple test will identify if an individual has a mutated CFTR gene and may be a carrier. In the U.S., prenatal tests are available to detect genetic mutations, and newborns are routinely screened for CF.

If you have the condition or think that you may be a carrier, talk with your doctor about testing for CF.

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Medical Reviewer: Nick Villalobos, MD
Last Review Date: 2023 Jan 24
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THIS TOOL DOES NOT PROVIDE MEDICAL ADVICE. It is intended for informational purposes only. It is not a substitute for professional medical advice, diagnosis or treatment. Never ignore professional medical advice in seeking treatment because of something you have read on the site. If you think you may have a medical emergency, immediately call your doctor or dial 911.
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