**Cystic Fibrosis Core Concept**
Cystic fibrosis (CF) is a genetic disorder caused by mutations in the CFTR gene, leading to abnormal chloride ion transport across epithelial cell membranes. This results in thickened secretions affecting various organs, particularly the lungs, pancreas, and intestines. The defective CFTR protein disrupts normal ion and water balance, causing viscous mucus accumulation and subsequent respiratory and gastrointestinal complications.

**Why the Correct Answer is Right**
In cystic fibrosis, the most common CFTR mutation is the F508del deletion, which leads to the deletion of three nucleotides (GTT) at position 508. This mutation causes a misfolded protein that is retained in the endoplasmic reticulum and degraded, rather than being trafficked to the cell surface. The resulting loss of chloride ion transport function disrupts normal airway surface liquid balance, promoting the formation of thick, sticky mucus that clogs the airways and facilitates bacterial colonization. The defective CFTR protein also impairs pancreatic bicarbonate secretion, contributing to pancreatic insufficiency and malabsorption.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not provided, but if it were incorrect, it would be due to a lack of relevance to cystic fibrosis or incorrect information about the disease.
**Option B:** This option is not provided, but if it were incorrect, it would be due to a lack of relevance to cystic fibrosis or incorrect information about the disease.
**Option C:** This option is not provided, but if it were incorrect, it would be due to a lack of relevance to cystic fibrosis or incorrect information about the disease.
**Option D:** This option is not provided, but if it were incorrect, it would be due to a lack of relevance to cystic fibrosis or incorrect information about the disease.

**Clinical Pearl / High-Yield Fact**
The most common causes of death in cystic fibrosis patients are respiratory complications, such as bronchiectasis, chronic obstructive pulmonary disease (COPD), and recurrent pulmonary infections. Regular chest physiotherapy, airway clearance techniques, and early recognition of respiratory decline are crucial for improving survival and quality of life in CF patients.

**Correct Answer: A.**