Cystic fibrosis (CF) is a chronic, inherited condition that affects glands producing sweat and mucus throughout the body. This genetic disorder causes these naturally thin, slippery body fluids to become abnormally thick and sticky. Understanding the genetic origins of CF is foundational for current research, screening methods, and targeted treatments. The disease affects multiple body systems, and its cause traces back to a specific location within the human genome.
Pinpointing the CF Gene Location
The gene causing cystic fibrosis is found on chromosome 7, one of the 23 pairs of chromosomes in human cells. This specific gene is officially named the Cystic Fibrosis Transmembrane Conductance Regulator, or CFTR. The CFTR gene is situated on the long arm of chromosome 7, in a region designated 7q31.2.
Cystic fibrosis occurs when an individual inherits mutations within the CFTR gene. Over 1,800 different mutations have been identified that can lead to the disease. The most common mutation, known as Delta F508, involves the deletion of three DNA building blocks.
The Essential Role of the CFTR Protein
The CFTR gene provides instructions for making the cystic fibrosis transmembrane conductance regulator protein. This protein functions as an ion channel, a specialized gate on the surface of epithelial cells. Epithelial cells line the passageways of many organs, including the lungs, pancreas, and sweat glands.
The channel’s primary job is to regulate the flow of negatively charged chloride ions and water across the cell membrane. By moving chloride ions outside the cell, the CFTR protein helps attract water to the cell’s surface. This regulated flow of salt and water keeps the mucus layer thin, hydrated, and easily movable. The protein also helps regulate the function of other ion channels, such as those that transport positively charged sodium ions.
Understanding CF Inheritance
Cystic fibrosis is categorized as an autosomal recessive disorder. This means an individual must inherit two mutated copies of the CFTR gene—one from each parent—to develop the condition. If a person inherits one normal gene and one mutated gene, they are considered a carrier.
A carrier does not typically show symptoms because the one functional gene copy produces enough healthy CFTR protein. When two parents are carriers, they have a 25% chance of having a child who develops CF. There is a 50% chance the child will be a carrier, and a 25% chance the child will inherit two normal gene copies.
How Genetic Changes Affect the Body
Mutations in the CFTR gene lead to a faulty CFTR protein that is either absent, improperly made, or unable to function correctly as a channel. This malfunction prevents the proper transport of chloride ions and water across cell membranes. When chloride ions are trapped inside the cells, the lack of water outside causes secretions to lose their normal hydration.
This cellular failure results in the characteristic thick, sticky mucus that clogs ducts and passageways throughout the body. In the lungs, this dehydrated mucus cannot be cleared, leading to chronic infections and progressive lung damage. The digestive system is also affected, as thick secretions block ducts in the pancreas, preventing the release of necessary enzymes. This malabsorption can lead to poor weight gain and nutritional deficiencies.