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CF Below
the Surface

Cystic fibrosis (CF) feels a little different for everyone. But it all starts with a problem within the cells. Mutations found on both copies of a specific gene cause proteins throughout the body to be made incorrectly. This results in a buildup of thick, sticky mucus in the lungs and beyond, leading to frequent inflammation and infections that can cause damage, even before it can be felt.

Siblings living with CF

Cause of CF

CF starts small—within the cells

Genes, which tell our bodies what our physical features will look like, are also the cause of certain diseases. A specific gene is responsible for CF. It’s called the cystic fibrosis transmembrane conductance regulator (CFTR) gene, and everyone has 2 CFTR genes—not just people with CF. This gene contains the instructions for producing CFTR proteins, which do an important job on the surface of certain cells throughout the body. But when someone has CF, a change in both copies of this gene (called a mutation) results in CFTR proteins that aren't able to do their job. Because of this, mucus, which is a slippery substance lining many different organs, gets too thick, causing infections and damage.

CF fact or fiction CF fiction CF fact or fiction CF fiction

If someone has a mutation in one of their CFTR genes, it means they’ll have CF.

Here's the truth:
In order for someone to have CF, they must have a mutation in both of their CFTR genes.


CFTR Protein Defects

Defects vary by mutation

Over 2,000 mutations in the CFTR gene have been discovered.

Over 2,000 mutations in the CFTR gene have been discovered

About 281 mutations
cause the range of different protein defects
that result in CF.

Defects vary by mutation

Watch the videos below to learn about these CFTR defects

All the CFTR mutations that cause CF result in thick, sticky mucus

There's one thing that remains the same across CF-causing CFTR protein defects—they all cause mucus in different parts of the body to thicken. Even if someone with CF doesn’t feel it, this mucus can cause damage from an early age. And although most people think of the lungs when they think of CF, other parts of the body are affected as well.

Impact on the Lungs Impact on the lungs

Starting from a young age, lung damage may occur before it can even be noticed

Thick, sticky mucus is found in the airways of the lungs and may cause symptoms such as wheezing, shortness of breath, and a persistent, phlegmy cough. This mucus buildup can’t be cleared from the airways easily. There is bacteria found in this mucus buildup as well, causing infection, inflammation, and scarring.

For someone with CF, a common bacteria in the respiratory tract is called Pseudomonas aeruginosa. If caught early, Pseudomonas aeruginosa should be treated immediately with antibiotics and may require continual treatment over time.

Increased inflammation from the mucus and bacteria clogging can cause damage to the airways, which often results in a condition called bronchiectasis

People with bronchiectasis have airways that are scarred and widened, making it harder to clear mucus. It also makes it difficult for air to move into and out of the airways. The buildup of mucus and germs can also lead to pulmonary exacerbations. Most people with CF are familiar with pulmonary exacerbations as periods of time when symptoms get more severe and may require intravenous (IV) antibiotics or a hospital visit. The lung damage caused by pulmonary exacerbations may be permanent.

31% of people living with CF experienced complications from asthma.

It’s important to have regular check-ins with care teams so they can monitor lung function.

Digestive System Impact

Thicker digestive juices damage organs

While CF is often thought of as a problem with the lungs, it also causes significant problems in the digestive system, particularly in the pancreas and liver.

The pancreas

Thick juices block the ducts within the pancreas, an organ in the digestive system that helps break down food. This blockage makes it harder for the digestive enzymes to reach the small intestine where they do their job.

Without these enzymes, the body has trouble breaking down food and absorbing nutrients. Not having these enzymes leads to:

  • Poor growth and slow weight gain, even if a lot of food is eaten
  • Frequent, greasy, and bulky stools

The liver

The liver is another part of the digestive system affected by this mucus. Inside the liver are tubes called ducts that are meant to drain it of bile. In people with CF, bile is thicker. As a result, the bile ducts can become blocked, leading to irritation or inflammation in the liver.

The intestines

Some people with CF may also experience distal intestinal obstruction syndrome (DIOS), a complete or incomplete blockage of the intestines due to thicker digestive juices.

Other Effects of CF

Mucus buildup also causes problems in other organs


  • Impact on the sinuses

    The sinuses produce mucus, which helps keep them clear by protecting them against dust, dirt, and bacteria. In someone with CF, the sinuses fill up with thick mucus that is difficult to clear out. If left untreated, the mucus blocks the sinuses, causing pressure and pain, which triggers inflammation that may contribute to nasal polyps. It also allows bacteria to grow, leading to sinus infections, such as sinusitis.

  • Nasal polyps

    Nasal blockage in someone with CF is commonly caused by nasal polyps. A nasal polyp is a growth in the nose that is filled with fluid or mucus and blocks where the sinuses drain into the nose. The mucus then builds up in the sinuses and contributes to sinusitis.

Children and adolescents with nasal polyps
  • Sinus disease

    CF can also cause sinusitis, which is inflammation, or swelling, in the sinus cavity. Mucus blocks the sinuses, leading to sinus infections and potentially lung function decline.


  • Impact in women

    For a woman who has CF, thick mucus in her reproductive system may make it difficult for sperm to travel to the uterus. This may make fertilization of a woman's eggs difficult.

  • Impact in men

    As a result of CF, men may experience fertility issues as well because the tubes through which sperm need to pass may not have formed, or they may be clogged with thick, sticky mucus. So although intercourse may be normal, a man with CF may deliver little or no sperm.

CF fact or fiction CF fiction CF fact or fiction CF fiction

CF is only a
disease of the

Here's the truth:
CF affects
many different
systems of
the body.


CF Video Source

CF gene mutations and defective CFTR proteins

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