A 4-month-old infant presents with progressive hypotonia, macroglossia, severe cardiomegaly on echocardiography, and elevated serum creatine kinase. Muscle biopsy shows vacuoles filled with periodic acid-Schiff positive material that stains strongly for acid phosphatase. Deficiency of which enzyme explains these findings?

• A Debranching enzyme (amylo-1,6-glucosidase)
• B Muscle myophosphorylase
• C Lysosomal alpha-1,4-glucosidase (acid maltase) ✓
• D Phosphofructokinase-1

Explanation

This is Pompe disease (glycogen storage disease type II), caused by deficiency of lysosomal alpha-1,4-glucosidase, so glycogen accumulates inside lysosomes rather than in the cytosol. The combination of hypertrophic cardiomyopathy, macroglossia, and hypotonia in infancy is characteristic. Myophosphorylase (type V) causes exercise intolerance without cardiomegaly, debranching enzyme (type III) causes hepatomegaly with short outer branches, and PFK-1 (type VII) causes hemolysis with exercise intolerance.

Reference: Nelson Textbook of Pediatrics, 22nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.