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Know Your Mutations: A CFTR Mutation Fact Sheet
Cystic Fibrosis is caused by mutations, or changes, in the CFTR gene. This gene provides the code that tells the body how to make the cystic fibrosis transmembrane conductance regulator (CFTR) protein. The protein controls the salt and water balance in the lungs and other tissues. All people have two copies of the CFTR gene, and there must be mutations in both copies to cause CF. More than 1,700 mutations of the CFTR gene have been identified. Although some are common, others are rare and found in only a few people.
CFTR mutations are grouped into classes based on the way the mutations affect the CFTR protein. The chart below shows the most common CFTR mutation classes. In the future, mutations may also be classified by "theratype," meaning which type of CFTR modulator therapy they respond to best. This is because mutations within the same class may respond to therapies differently, and not every mutation can be neatly assigned to one mutation class.
Certain types of CFTR mutations are associated with different disease complications. For example, some mutations are more likely to affect the pancreas than others. However, this correlation is not perfect, and knowing an individual's CFTR mutations cannot always tell you how severe that person's CF symptoms will be.
Although the potential therapies described below can be very effective for some people with CF, others may not experience the exact same benefit. Researchers continue to work in the lab and in clinical trials to find the best therapeutic approaches to target specific CFTR mutations or classes of mutations to improve the health of all individuals living with CF.
Figure 1.1: Source: https://www.cff.org/What-is-CF/Genetics/Know-Your-CFTR-Mutations-Infographic.pdf
Cystic Fibrosis Transmembrane Conductance Regulator: Assessing Function
Photo courtesy of Greg Montgomery
Nasal potential difference (NPD) and intestinal current measurements (ICM) are alternate methods of assessing CFTR function that are available through research programs in some regions. These methods are rarely applied to infants with a positive newborn screening test, but may be helpful in older children and adults with inconclusive diagnostic findings.
CFTR-related disorder refers to clinical symptoms of cystic fibrosis in one organ system and laboratory findings suggesting abnormal CFTR function as an etiology, without diagnostic criteria for CF. Laboratory findings may include the presence of one or more CFTR mutations, or abnormal NPD or ICM, but with a sweat chloride less than 60 mmol/L. Congenital bilateral absence of the vas deferens, recurrent acute pancreatitis, and bronchiectasis are the best described of these syndromes.