Cystic Fibrosis

Cystic Fibrosis

Cystic fibrosis (CF) is an inherited chronic disease that affects the lungs and digestive systems of about 30,000 children and adults in the United States (70,000 worldwide). A defective gene causes the body to produce unusually thick, sticky mucus that clogs the lungs, obstructs the pancreas and stops natural enzymes from helping the body break down and absorb food. Cystic fibrosis occurs when there is a mutation in the CFTR gene. The protein created by this gene is anchored to the outer membrane of cells in the sweat glands, lung, pancreas, and other affected organs. The protein spans this membrane and acts as a channel connecting the inner part of the cell to the surrounding fluid. This channel is primarily responsible for controlling the movement of chloride ions across the membrane. When the CFTR protein does not work, chloride is trapped outside the cell. Because chloride is negatively charged, positively charged ion passage is also affected.

How this malfunction of cells in cystic fibrosis causes the medical manifestations of CF is not well understood. One theory suggests that the lack of chloride absorption through the CFTR protein leads to the accumulation of nutrient-rich mucus in the lungs which allows bacteria to hide from the body's immune system. Another theory proposes that the CFTR protein failure leads to a paradoxical increase in sodium and chloride uptake, which, by leading to increased water reabsorption, creates dehydrated and thick mucus. Yet another theory focuses on abnormal chloride movement out of the cell, which also leads to dehydration of mucus, pancreatic secretions, bile secretions, etc. These theories all support the observation that the majority of the damage in CF is due to blockage of the narrow passages of affected organs with thickened secretions. These blockages lead to remodeling and infection in the lung, damage by accumulated digestive enzymes in the pancreas, blockage of the intestines by thick feces, etc...