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Cystic fibrosis is caused by a genetic defect in the CFTR (cystic fibrosis transmembrane conductance regulator) gene. This gene provides instructions for producing the CFTR protein, which acts as a channel in the membrane of cells and regulates the transport of negatively charged particles called chloride ions into and out of cells. The regulation of chloride transport is crucial for the proper functioning of several organs, particularly the lungs and pancreas.

The genetic defect in the CFTR gene can result in several different types of mutations, which produce a CFTR protein with reduced or no function. When the CFTR protein is not functioning correctly, it causes an imbalance in the transport of chloride ions and other ions such as sodium across the cell membrane. This means that the ion regulation necessary for normal cellular processes is disrupted.

The improper cellular transport resulting from the defective CFTR protein leads to several key symptoms of cystic fibrosis: 1. In the lungs: The imbalance in ion transport causes a dehydration of the airway surface liquid, leading to the production of thick, sticky mucus. This mucus can obstruct the airways, which makes it difficult to breathe and increases the risk of infections as bacteria can easily get trapped in the mucus. 2. In the pancreas: The thick mucus can also block the ducts of the pancreas, which inhibits the release of digestive enzymes. This results in malabsorption of nutrients and can cause difficulty in maintaining weight, growth issues, and deficiencies in fat-soluble vitamins. 3. In the liver: The defective CFTR protein can cause bile ducts in the liver to become blocked, leading to liver diseases. 4. In the reproductive system: The thick mucus can cause blockages in the reproductive organs, such as the vas deferens in males, which can lead to fertility issues. By understanding the role of the CFTR gene and how its defect affects cellular transport, we can link this genetic defect to the symptoms observed in cystic fibrosis patients.