All are true about cystic fibrosis except?
## Core Concept
Cystic fibrosis (CF) is a genetic disorder that primarily affects the lungs and digestive system, caused by mutations in the **CFTR (cystic fibrosis transmembrane conductance regulator) gene**. This gene encodes for a protein that functions as a channel transporting chloride ions across cell membranes. The defective CFTR protein leads to thick, viscous secretions that clog the airways and trap bacteria, resulting in recurrent respiratory infections and pancreatic insufficiency.
## Why the Correct Answer is Right
The correct answer is related to the understanding that cystic fibrosis is characterized by its impact on exocrine glands, notably causing **pancreatic insufficiency** and **respiratory failure** due to chronic infections and inflammation. A key feature is the production of **thick, sticky mucus** that clogs the airways. The most common mutation leading to CF is the **F508del mutation**, which results in a misfolded protein that is degraded before it can reach the cell surface.
## Why Each Wrong Option is Incorrect
- **Option A:** Typically, cystic fibrosis leads to **increased sodium absorption** and **increased chloride secretion** is impaired, not directly related to an option provided but understanding its effects on ion transport is crucial.
- **Option B:** CF often results in **malabsorption** due to pancreatic insufficiency, making this statement potentially true and not the answer.
- **Option C:** This option could relate to various aspects of CF pathology; without specifics, it's challenging to address directly, but generally, CF involves **lung damage** and **digestive issues**.
- **Option D:** If an option suggests that CF does not affect a particular system or implies a mechanism not consistent with CF, it would be incorrect based on the established pathophysiology.
## Clinical Pearl / High-Yield Fact
A key clinical pearl is that patients with cystic fibrosis are at increased risk of **developing diabetes mellitus** due to pancreatic damage. Another important point is the **screening for CF** in newborns, which is done to allow for early intervention and improved outcomes. Lastly, **sweat chloride testing** remains the gold standard for diagnosing cystic fibrosis.
## Correct Answer: D.