A 24-year-old man has recurrent sinopulmonary infections since childhood. Chest CT shows cylindrical dilatation of segmental bronchi extending to the lung periphery. He also reports anosmia and has situs inversus on imaging. Which ultrastructural defect underlies his lung disease?

• A Absence of dynein arms in ciliary axonemes ✓
• B Defective alpha-1 antitrypsin folding in hepatocytes
• C Mutation of the CFTR chloride channel
• D Deficiency of surfactant protein B

Explanation

Situs inversus with bronchiectasis and sinusitis defines Kartagener syndrome, a variant of primary ciliary dyskinesia caused by absent or shortened dynein arms, producing immotile cilia and defective mucociliary clearance. CFTR mutation causes bronchiectasis in cystic fibrosis but does not produce situs inversus, which kills option C. Alpha-1 antitrypsin deficiency causes panacinar emphysema and liver cirrhosis, not ciliary defects.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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