In cystic fibrosis, mutations in the CFTR gene lead to which change in airway secretions?

• A. Thick, viscous secretions obstruct airways
• B. Thin, watery secretions
• C. No effect on secretions
• D. Decreased mucus production

Answer: (A)

Mutations in CFTR disrupt chloride transport in the airway epithelium, which reduces water content in the airway surface liquid. The dehydrated surface becomes thick and sticky mucus that is hard to clear by cilia, leading to mucus plugs that obstruct airflow. This is why thick, viscous secretions obstruct airways is the correct description. The other options describe secretions that would not reflect CF pathology (thin watery mucus, no effect, or decreased mucus production), whereas CFTR mutations cause the mucus to become abnormally thick and adhesive, promoting obstruction and infection.