True about cystic fibrosis
**Core Concept**
Cystic fibrosis is a genetic disorder characterized by the production of thick, sticky mucus that clogs the airways and digestive system. This is due to mutations in the CFTR gene, which encodes for a chloride channel responsible for regulating salt and water balance in epithelial cells.
**Why the Correct Answer is Right**
The defective CFTR protein leads to abnormal chloride transport, resulting in a decrease in chloride secretion into the airway lumen. This increase in sodium absorption and decrease in chloride secretion cause water to be absorbed from the airway lumen, leading to thick and dehydrated mucus. The accumulation of this mucus in the airways is responsible for the recurrent respiratory infections and bronchiectasis seen in cystic fibrosis patients.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because cystic fibrosis is primarily caused by mutations in the CFTR gene, not the alpha-1 antitrypsin gene.
**Option B:** This option is incorrect because the primary defect in cystic fibrosis is not an overproduction of mucus, but rather an abnormality in the chloride transport across epithelial cells.
**Option C:** This option is incorrect because the primary manifestation of cystic fibrosis is not an increase in sweat gland secretion, but rather an increase in sweat gland chloride concentration due to the abnormal CFTR function.
**Clinical Pearl / High-Yield Fact**
Cystic fibrosis is a classic example of a monogenic disorder with a significant impact on multiple organ systems, highlighting the importance of genetic testing and counseling in the management of this disease.
**Correct Answer: D.**