Cystic Fibrosis | Symptoms & Causes

What are the symptoms of cystic fibrosis?

The type, severity and symptoms of cystic fibrosis (CF) differ for each child, and some children may not show signs of CF until later in life. Infants born with CF usually show symptoms within the first year. These symptoms include:

  • skin that tastes salty
  • frequent lung infections,  bronchitis or pneumonia 
  • chronic sinus infection
  • persistent cough
  • recurrent diarrhea
  • foul-smelling or greasy stools
  • stunted growth

CF respiratory-system symptoms

Symptoms related to the respiratory system include:

  • frequent lung and sinus infections
  • chronic cough
  • coughing up blood
  • clubbing (rounding and enlargement of the fingers and toes)
  • heart enlargement
  • nasal polyps (fleshy growths in the nose)
  • sinusitis (inflamed nasal sinuses)

Normally, mucus is thin and passes easily through the airways. With CF, mucus becomes thick, sticky and gradually blocks the airways. Eventually, cysts may develop due to this blockage.

Lung infections are common in children with CF because bacteria that are normally cleared by the airways remain in the thickened mucus. Two bacteria, pseudomonas aeruginosa and staphylococcus (staph) bacteria, are the major culprits in causing CF-related lung infections.

About 10 to 20 percent of children with CF have nasal polyps — small protrusions of tissue from the lining of the nose — that need to be surgically removed. Children with CF also have a high rate of sinus infections.

CF digestive-system symptoms

Symptoms related to the digestive system include:

  • frequent, bulky, greasy stools
  • fat in the stools
  • rectal prolapse (a condition in which part of the lower intestinal tract comes out of the anus)
  • stomach pain
  • bloody diarrhea
  • poor growth
  • gallstones

The gene that has the CF mutation — the CFTR gene — controls the flow of water and certain salts in and out of the body's cells. The mutation causes mucus to become thick throughout a child’s body and block passageways between organs.

The pancreas secretes digestive enzymes that break down food and provide nourishment for the rest of the body. In around 90 percent of children with CF, the ducts leading from the pancreas to other organs become blocked. As a result, children with CF have difficulty absorbing key nutrients, especially:

  • fats
  • some proteins
  • fat-soluble vitamins such as A, D, E and K

CF-related diabetes symptoms

Because the symptoms are so similar, cystic fibrosis-related diabetes (CFRD) often goes undetected in children with diabetes. The symptoms of CFRD include:

  • frequent need to pee
  • increased thirst
  • losing weight for no apparent reason
  • exhaustion
  • loss of lung function 

The American Diabetes Association and Cystic Fibrosis Foundation recommend children with CF be tested for diabetes with an oral glucose tolerance test every year once they turn 10.

CF liver disease symptoms

As more people with CF live longer, more are developing cystic fibrosis liver disease (CFLD). With CFLD, the liver becomes scarred over time from impaired bile flow. In the most severe cases, such scarring can lead to cirrhosis, however, this is rare. About 30 percent of patients with CF develop liver disease while only 2 to 8 percent develop cirrhosis.

CFLD may not show signs or become symptomatic until puberty or later. Signs and symptoms may include:

  • abnormal liver blood tests
  • abnormal appearance of liver on radiology tests
  • enlarged liver
  • swollen abdomen
  • yellowish skin
  • vomiting of blood

What causes cystic fibrosis?

Because cystic fibrosis is a genetic disease, there are two ways to look at what causes it — how it occurs on the cellular level and how a child inherits CF.

What happens at the cellular level

As the name implies, a “genetic disease” is caused by something in the body’s genes. Genes are found on chromosomes — structures in the cells that usually come in pairs.

One pair of chromosomes includes a gene called the cystic fibrosis transmembrane conductance regulator (CFTR) gene. This gene is large and complex, in fact, more than 1000 different CF-related mutations have been identified.

In most people, the CFTR gene helps regulate the flow of salt and fluid in and out of cells. But if there is a mutation in this gene, chloride, a component of salt, gets stuck inside the cells and thick, sticky mucus starts to build up inside the body.

How a child inherits CF

If a baby is born with CF, it means the baby inherited two CF genes, one from the mother and one from the father.

A person with only one CF gene is healthy and said to be a "carrier" of the disease. If both parents carry the CF gene, they each have one copy of the defective gene, but do not have the disease themselves. Their children have:

  • a 25 percent chance of inheriting both defective copies and having CF
  • a 50 percent chance of inheriting one defective copy and being a carrier
  • a 25 percent chance of not having CF and not carrying the gene