A 5-year-old boy presents with progressive proximal muscle weakness, Gower sign, and markedly elevated serum creatine kinase (20,000 U/L). Genetic testing confirms a deletion in the DMD gene. Which of the following best describes the functional consequence of the absent protein in this condition?

• A Impaired cross-linking of collagen fibers, leading to joint hypermobility
• B Loss of structural linkage between the cytoskeleton and extracellular matrix, causing sarcolemmal instability ✓
• C Defective microtubule assembly, impairing intracellular transport in neurons
• D Abnormal ion channel gating, resulting in episodic muscle paralysis

Explanation

Duchenne muscular dystrophy results from mutations in the DMD gene encoding dystrophin. Dystrophin links intracellular actin cytoskeleton to the extracellular matrix via the dystrophin-glycoprotein complex, stabilizing the sarcolemma during contraction. Absence causes membrane fragility, calcium influx, and progressive myofiber necrosis. Option A describes collagen defects seen in Ehlers-Danlos. Option C refers to neuronal transport defects. Option D describes channelopathies like periodic paralysis.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.