**Core Concept:** Cystic Fibrosis (CF) is a genetic disorder caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. The CFTR gene encodes a protein that regulates the movement of salt and water across cell membranes, particularly in the respiratory, digestive, and reproductive systems. The primary pathophysiology involves the production of thick, sticky mucus that leads to inflammation, infection, and obstruction of airways, pancreas, and other organs.

**Why the Correct Answer is Right:** Option C is correct because cystic fibrosis patients do not exhibit impaired pancreatic function. While the disease primarily affects the respiratory system, it also impacts the pancreas, leading to malabsorption and secondary nutritional deficiencies.

**Why Each Wrong Option is Incorrect:**

A. False: Cystic fibrosis does not cause immune system dysfunction. Although the thickened mucus can lead to recurrent infections, the disease itself does not impair the immune system.

B. False: Cystic fibrosis does not primarily affect the cardiovascular system. The disease primarily involves respiratory, digestive, and reproductive systems, while cardiovascular involvement is rare and usually due to complications like pulmonary hypertension.

D. False: Cystic fibrosis does not primarily affect the renal system. While the disease can impact the kidneys, it is not the primary site of involvement, and the respiratory, digestive, and reproductive systems are more commonly affected.

**Clinical Pearl:** The correct understanding of cystic fibrosis's organ-specific manifestations is crucial for appropriate diagnosis and management. Differential diagnosis should consider other diseases with overlapping symptoms, such as primary ciliary dyskinesia, primary immunodeficiency disorders, and chronic granulomatous disease.