Genetics Northern California

Cystic Fibrosis

What is cystic fibrosis?
How common is cystic fibrosis?
What causes cystic fibrosis?
How is cystic fibrosis inherited?
How is cystic fibrosis diagnosed?
Can cystic fibrosis be diagnosed during pregnancy?
How is cystic fibrosis treated?
Where can I get more information about cystic fibrosis?

What is cystic fibrosis?
Cystic fibrosis (CF) is a genetic disorder that causes buildup of thick, sticky mucus in the body’s organs. Mucus helps protect the linings of many parts of the body. However, people with CF make mucus that is thicker than normal. This type of mucus can lead to lung damage, and interfere with the digestive tract and the reproductive system. Symptoms of CF are highly variable. Most people are diagnosed in childhood, but some people with mild symptoms may not be diagnosed until adulthood. Although CF doesn’t affect the way a person looks, people with CF who have digestive problems may be thinner and slightly shorter than average. 

Having thick mucus causes symptoms in three main areas:
Respiratory Symptoms

  • Long-lasting cough with increased phlegm
  • Difficulty breathing/Wheezing
  • Sinus disease (inflammation or infection of the sinuses)
  • Frequent lung infections
Digestive Symptoms
  • Pancreatic insufficiency - This means that the enzymes made in the pancreas do not get into the bloodstream as much as they need to. Enzymes from the pancreas are important to digest food and help maintain normal blood-sugar levels.
  • Slow growth (failure to thrive)
  • CF-related diabetes
  • Recurrent pancreatitis (inflammation of the pancreas)
  • Liver disease
  • Salt-loss syndromes or salt-wasting (high levels of salt being released from the body in sweat)
  • Meconium ileus - This is when the first stool of a newborn is thicker than usual and gets stuck in a part of the small intestine called the ileum. This can cause a complete blockage in the intestine at birth and requires urgent treatment.
  • Vitamin deficiencies
Reproductive Symptoms
  • Male infertility (due to absence of the vas deferens caused by a blockage of mucus during development)

How common is cystic fibrosis?
Cystic fibrosis is one of the most common genetic disorders among the Caucasian population. CF occurs in about 1 in 2,500 to 3,500 Caucasian births. CF is less common in other ethnic groups, but has been reported in all populations. Males and females are equally likely to have CF.  

What causes cystic fibrosis?
CF is caused by mutations in both copies of a person’s CF gene. The CF gene codes for a chloride channel protein called CFTR (cystic fibrosis transmembrane conductance regulator). This protein is important for cells located inside the lungs and digestive tract (epithelial cells). When both copies of the CF gene have a mutation, the chloride channel is unable to regulate chloride levels normally. This results in 1) high levels of sodium chloride (salt) being released out of the body in sweat, and 2) the production of the thickened mucus. 

How is cystic fibrosis inherited?
Cystic fibrosis is an autosomal recessive disorder. This means that for two parents to have a child with CF, they both must carry a non-working CF gene. Carriers usually do not have symptoms, and most often do not know they are carriers. When both parents are CF carriers,  each child has a 25% chance of having CF, a 50% chance of being a carrier, and a 25% chance of not inheriting either CF mutation.

How is cystic fibrosis diagnosed?
Most individuals with CF are now identified through newborn screening. To confirm a suspected diagnosis, more definitive testing is done.

The diagnosis of cystic fibrosis can be made by the following tests:
Sweat chloride test: The sweat chloride test measures the amount of chloride in the person’s sweat. A person with CF has roughly 2 to 6 times the amount of chloride in a person without the disorder. This is the “gold standard” test to diagnose CF.
DNA testing: DNA testing looks directly at the CF gene for mutations. Testing is usually done on a blood sample. This test can confirm a diagnosis, as well as identify carriers. However, the CF gene has many possible mutations, not all of which cause CF. As a result, DNA testing is not always definitive for people without the common mutations (called disease-causing mutations).

Can cystic fibrosis be diagnosed during pregnancy?
Yes. Prenatal testing is available for couples known to be at-risk for having a child with CF.  Couples may be identified as CF carriers through routine carrier screening or by having a history of CF in the family. 

How is cystic fibrosis treated?
There is no cure for CF, but treatments are improving. Individuals with this condition usually require daily chest therapy, medications, and periodic hospitalizations.  It is recommended that patients with CF be routinely seen in a specialty clinic due to the varying severity and symptoms of this disorder.

Where can I get more information about cystic fibrosis?
Genetics Home Reference - General information and links about cystic fibrosis provided by the National Library of Medicine.
The Cystic Fibrosis Foundation - Provides support to individuals with cystic fibrosis and their families.
GeneReview of CFTR-related disorders  – A more in-depth look at the diagnoses and management for those with a CFTR mutation.

 

Last updated:   July 2013
Update by:        Sara Mokhtary
                        Kimberly Barr, MS, LCGC

Last reviewed: July 2013
Reviewed by:   Kaiser Genetics Department