Cystic Fibrosis | Symptoms & Causes

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 1,000 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 a thick, sticky mucus starts to build up inside the body.

How cystic fibrosis is inherited

Cystic fibrosis is a genetic disease, meaning it is passed down through the parents. When a baby is born with cystic fibrosis, they have inherited two cystic fibrosis genes, one from the mother and one from the father.

A person with only one cystic fibrosis gene is healthy and said to be a "carrier" of the disease. If both parents carry the cystic fibrosis 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 cystic fibrosis
  • 50 percent chance of inheriting one defective copy and being a carrier
  • 25 percent chance of not having cystic fibrosis and not carrying the gene

What are the symptoms of cystic fibrosis?

Infants born with cystic fibrosis typically show signs within the first year. Cystic fibrosis can affect different organs and systems in a number of ways.

Respiratory symptoms of cystic fibrosis

Cystic fibrosis symptoms related to the respiratory system can 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)

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

Digestive symptoms of cystic fibrosis

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 cystic fibrosis, the ducts leading from the pancreas to other organs become blocked. This causes difficulty absorbing key nutrients, including fats, some proteins, and fat-soluble vitamins such as A, D, E and K.

Cystic fibrosis tools

The Cystic Fibrosis Center at Boston Children’s Hospital is exploring new tools and approaches to support patients and families by helping them better manage their disease and improve their quality of life.

The Cystic Fibrosis Center at Boston Children’s Hospital is exploring new tools and approaches.

Cystic fibrosis-related diabetes symptoms

Cystic fibrosis-related diabetes (CFRD) often goes undetected in children with cystic fibrosis. 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 the Cystic Fibrosis Foundation recommend children with cystic fibrosis be tested for diabetes with an oral glucose tolerance test every year once they turn 10.

Cystic fibrosis-related liver disease symptoms

As more people with cystic fibrosis 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 cystic fibrosis develop liver disease, while only two to eight percent develop cirrhosis.

People with CFLD may not have symptoms until puberty or later. These may include:

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