Reviewed by Sara Brayshaw, MS, RN Jerry A. Nick, MD

What Causes Cystic Fibrosis?

Cystic fibrosis (CF) is a genetic disease caused by a mutation in a gene named the cystic fibrosis transmembrane conductance regulator (CFTR). The inheritance pattern is autosomal recessive. Thus, to have the diagnosis of CF, an individual must have two defective CFTR genes, by inheriting a mutant copy of the CFTR gene from both mother and father. People with a single CFTR mutation are termed “carriers,” and do not have symptoms of CF.

 

How is Cystic Fibrosis Inherited?

There are about 1,800 different CFTR mutations that can cause CF. The most common mutation is named F508del, and approximately two-thirds of all CFTR mutations worldwide are F508del. While having 2 copies (homozygote) of F508del has historically been associated with severe disease, many of the less common mutations are associated with less severe clinical symptoms. Detailed information about known CFTR mutations is available from scientists at Johns Hopkins University and the Hospital for Sick Children in Toronto, Canada.

The CFTR gene is responsible for the production of the CFTR protein, which is a channel for the passage of salt (sodium and chloride ions) onto the surface of a variety of tissues. The CFTR protein contributes to the normal secretions produced in the airways, pancreatic ducts, sweat ducts, sinuses and bowels. When the CFTR protein is not present, the result is mucus that is unusually thick, dehydrated and sticky. Most of the complications of CF arise from damage to the pancreas and lungs, caused by this abnormal mucus. Later in life, the most significant complications are due to infections that have taken advantage of the damaged lungs and that are often impossible to eradicate.

Diagram of how cystic fibrosis is inherited

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