An 8-month-old infant presents with poor feeding, macroglossia, severe hypotonia, and biventricular cardiac failure. Echocardiography shows massive concentric hypertrophy of both ventricles. ECG shows short PR interval with tall QRS complexes. Muscle biopsy shows vacuoles filled with PAS-positive material that stains positive on acid phosphatase assay. Which enzyme is deficient?
- A Lysosomal alpha-1,4-glucosidase (acid maltase) ✓
- B Muscle phosphorylase
- C Debranching enzyme
- D Phosphofructokinase
Correct answer: A. Lysosomal alpha-1,4-glucosidase (acid maltase)
Explanation
This is Pompe disease (glycogen storage disease type II), caused by deficiency of lysosomal acid maltase. Glycogen accumulates inside lysosomes, giving membrane-bound vacuoles, and the heart is characteristically massively hypertrophied with macroglossia. The acid phosphatase positivity reflects the lysosomal origin. McArdle disease (myophosphorylase deficiency) causes exercise intolerance with normal cardiac size, and Cori disease lacks cardiomegaly as a dominant feature.
Reference: Nelson Textbook of Pediatrics, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.