A 2-year-old child with recurrent respiratory infections is found to have immotile bronchial cilia on electron microscopy showing absent dynein arms. This primary ciliary dyskinesia (Kartagener syndrome with situs inversus) is caused by mutation in which structural protein?

• A Connexin 26 (GJB2) — gap junction protein causing hearing loss
• B Dynein heavy chain (DNAI1/DNAI2/DNAH5) — outer or inner dynein arm proteins ✓
• C Dystrophin — cytoskeletal protein linking actin to extracellular matrix
• D Fibrillin-1 — extracellular matrix glycoprotein mutated in Marfan syndrome

Explanation

Primary ciliary dyskinesia (Kartagener syndrome when associated with situs inversus) results from mutations in genes encoding ciliary dynein arm proteins, most commonly DNAI1, DNAI2, or DNAH5 (outer dynein arm) or DNAH11 (inner dynein arm). Dynein ATPase provides the force for ciliary beating; absent dynein arms render cilia immotile, causing bronchiectasis, sinusitis, male infertility, and situs inversus (normal left-right axis determination depends on nodal cilia in the embryo).

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.