A 2-year-old boy has marked hepatomegaly with mild fasting hypoglycemia that is less severe than expected from liver size. Liver biopsy shows normal glycogen structure. Family history suggests X-linked inheritance. Enzyme assay would most likely show deficient activity of:

• A Glucose-6-phosphatase
• B Acid alpha-glucosidase
• C Glycogen synthase
• D Hepatic phosphorylase kinase ✓

Explanation

Phosphorylase kinase deficiency (glycogen storage disease type IX) is usually X-linked (alpha subunit, PHKA2 gene) and produces hepatomegaly with mild hypoglycemia because phosphorylase itself is normal but cannot be activated. Glycogen structure remains normal. Glucose-6-phosphatase deficiency (type I) gives severe hypoglycemia with lactic acidosis and hyperuricemia, while acid alpha-glucosidase deficiency (type II) presents with cardiomyopathy rather than isolated hepatomegaly.

Reference: Nelson Textbook of Pediatrics, 22nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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