An 8-month-old infant presents with progressive hypotonia, macroglossia, and massive cardiomegaly leading to cardiac failure. Liver size is mildly increased, blood glucose is normal even after fasting, and there is no lactic acidosis. Muscle biopsy shows vacuoles filled with PAS-positive material that stains strongly for acid phosphatase. The deficient enzyme is located in which cellular compartment?

• A Cytosol
• B Mitochondrial matrix
• C Lysosome ✓
• D Endoplasmic reticulum membrane

Explanation

This is Pompe disease (GSD type II), caused by deficiency of lysosomal acid alpha-1,4-glucosidase (acid maltase). Because cytosolic glycogenolysis and gluconeogenesis are intact, blood glucose remains normal, distinguishing it from hepatic GSDs like von Gierke disease. The vacuoles are lysosomes engorged with autophagocytosed glycogen, hence lysosomal acid phosphatase staining. Enzyme replacement therapy with alglucosidase alfa is available.

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.