**Question:** True about Kartagener's syndrome is all except-

A. **Kartagener's syndrome** is a disorder affecting the cilia and is characterized by chronic bronchitis, bronchiectasis, and situs inversus.
B. It is caused by a deficiency in mucociliary clearance, leading to recurrent infections.
C. It is primarily associated with cystic fibrosis.
D. It is caused by a mutation in the CFTR gene.

**Correct Answer: D.**

**Core Concept:**
Kartagener's syndrome is a motile ciliary dyskinesia characterized by dysfunction of the primary cilia and secondary cilia found in the respiratory tract and in the genitourinary tract. This results in mucus retention, leading to chronic bronchitis, bronchiectasis, and situs inversus.

**Why the Correct Answer is Right:**
Kartagener's syndrome is primarily caused by a deficiency in mucociliary clearance due to abnormal movement of the cilia, leading to recurrent infections, and is not associated with cystic fibrosis or a mutation in the CFTR gene. Cystic fibrosis is a separate condition caused by mutations in the CFTR gene, which leads to thick mucus production in various organs, including the respiratory tract. Kartagener's syndrome and cystic fibrosis are distinct entities with different genetic causes.

**Why Each Wrong Option is Incorrect:**

A. Kartagener's syndrome and cystic fibrosis are distinct entities with different clinical presentations and genetic basis. While Kartagener's syndrome is characterized by impaired ciliary movement and recurrent infections, cystic fibrosis is caused by mutations in the CFTR gene, leading to thick mucus production in multiple organs.

B. Although mucociliary clearance is impaired in Kartagener's syndrome, it is not solely caused by a deficiency in mucociliary clearance. The primary cilia dysfunction is what distinguishes Kartagener's syndrome from cystic fibrosis.

C. While Kartagener's syndrome and cystic fibrosis are distinct entities, situs inversus is a common feature in Kartagener's syndrome but not a defining feature of cystic fibrosis.

D. Kartagener's syndrome is primarily caused by mutations in the CFTR gene, which is associated with cystic fibrosis, not Kartagener's syndrome. The CFTR gene is responsible for cystic fibrosis, while Kartagener's syndrome is caused by primary ciliary dyskinesia.

**Clinical Pearl:**
Situs inversus is a common feature in Kartagener's syndrome but is not a defining feature of cystic fibrosis. The presence of situs inversus may be helpful in distinguishing between the two conditions. Cystic fibrosis is a separate condition caused by mutations in the CFTR gene, while Kartagener's syndrome results from primary ciliary dyskinesia affecting the cilia in the respiratory tract.