Cystic fibrosis (CF) is a life-limiting, genetic disease that affects approximately 85,000 individuals worldwide.
What is cystic fibrosis?
CF causes dysfunction across many organs, though the most life-limiting complication occurs in the lungs through repeated infectious respiratory exacerbations. These episodes lead to the destruction of airways, chronic inflammation, and deterioration in lung function. Other manifestations of CF also include digestive, metabolic, and reproductive disruptions.
Improvement in disease management and disease-modifying drugs (CFTR modulators) have increased the life expectancy of people with CF. Despite advances, people with CF still experience loss in lung function, frequent exacerbations, and multisystemic complications that lead to a shorter life span. Additionally, the burdensome daily respiratory treatments further decrease the quality of life of people with CF.
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MODULATORS AND PIPELINE
What is the CFTR protein?
CF is caused by a mutation in the cystic fibrosis transmembrane conductance regulator (CFTR) gene.
The CFTR gene encodes for CFTR, a protein that functions as a chloride channel and regulates ion flow across the cell membrane of cells that line the surface of many organs such as the lungs and gut.
For the CFTR protein to function properly, it needs to be adequately produced and transported to the cell’s surface.
More than 2,000 CFTR mutations have been identified, and there are many mutations that have not yet been studied to determine which class they belong to. Some mutations result in hardly any CFTR function, others are associated with some residual function, and many more still require further studies to be understood.
Individuals with CF must inherit two disease-causing mutations in the CFTR gene, one from each parent. Individuals with two identical CF-causing mutations are homozygous for that mutation, whereas individuals with two different CF-causing mutations are heterozygous for those mutations.
CF-causing mutations are categorized into different classes based on their impact on the CFTR protein
- Class I mutations lead to CFTR protein not being made and also include nonsense mutations, most frameshift mutations, and large deletions.
- Class II mutations lead to misfolded or misshapen CFTR protein with little or none being present on the cell surface. The Class II F508del mutation is the most prevalent CF-causing mutation, affecting up to 90% of people with CF worldwide ~50% are homozygous for F508del and another ~40% are heterozygous for F508del.
- Class III mutations, or “gating mutations”, lead to reduced or no CFTR channel opening at the cell surface, resulting in reduced chloride ion movement through the CFTR channel. The most common gating mutation is G551D.
- Class IV mutations, or “conductance mutations”, lead to misshapen CFTR channels at the cell surface, resulting in restricted chloride ion movement through the CFTR channel. The most common conductance mutation is R117H.
- Class V mutations, or “splicing mutations”, lead to extremely reduced synthesis of normal CFTR, resulting in less CFTR protein at the cell surface.