What is the pathophysiology of cystic fibrosis?

Cystic fibrosis is primarily caused by a mutation in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. This defect interferes with the movement of chloride ions across epithelial cell membranes, which leads to an imbalance in salt and water transport in various organs. As a result, there is a significant loss of sodium and chloride in sweat, which is why individuals with cystic fibrosis often have salty skin.

The impaired chloride transport ultimately leads to the production of thick and sticky mucus in the lungs, digestive system, and other organs. In the lungs, this thick mucus obstructs airways, creates an environment prone to infections, and causes difficulty in breathing. The hallmark of cystic fibrosis is thus chronic respiratory issues stemming from the accumulation of this abnormal mucus, making the choice regarding the defective gene and its impact on mucus secretion the correct answer.

This provides a comprehensive understanding of the disease's pathophysiology, underscoring the importance of the CFTR gene in maintaining normal respiratory and digestive function through adequate ion transport and mucus production.