A 4-Month-Old Boy Is Brought to the Office Due to Difficulty

A 4-month-old boy is brought to the office due to difficulty feeding.  His mother says that he has difficulty holding his head up while breastfeeding and his suckling seems weaker than usual.  Weight is at the 5th percentile.  Length and head circumference are tracking along the 25th percentile.  Physical examination shows hepatomegaly and hypotonia in all 4 limbs.  Cardiac auscultation shows a gallop rhythm, and chest x-ray reveals severe cardiomegaly.  Muscle biopsy shows enlarged lysosomes containing periodic acid-Schiff (PAS) -positive material.  Which of the following enzymes is most likely deficient in this patient?

A) Acid alpha-glucosidase
B) Galactokinase
C) Glucose-6-phosphatase
D) Glycogen debrancher enzyme
E) Glycogen phosphorylase
F) Pyruvate kinase

Correct Answer:

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