A 6-year-old boy has recurrent sinusitis, otitis media, bronchiectasis and situs inversus. Electron microscopy of his nasal mucosa shows an absence of the outer and inner dynein arms of the ciliary axoneme. Which structure is directly affected by this defect?

• A The 9+0 arrangement of peripheral microtubule doublets
• B The glycoprotein glycocalyx on the ciliary surface
• C The basal body anchoring the cilium to the cell
• D ATPase motor activity required for microtubule sliding ✓

Explanation

This is Kartagener syndrome, a subset of primary ciliary dyskinesia. Dynein arms are ATPase motor proteins that generate sliding between adjacent microtubule doublets of the 9+2 axoneme, producing ciliary bending. Without them, cilia are immotile, causing defective mucociliary clearance and failure of embryonic nodal rotation leading to situs inversus. The basal body and the 9+2 pattern are structurally intact, and the glycocalyx plays no motility role.

Reference: Ross and Pawlina Histology: A Text and Atlas, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.