**Core Concept**
Von Gierke’s disease is a rare inherited glycogen storage disorder caused by a deficiency of glucose-6-phosphatase, an enzyme critical for gluconeogenesis and glycogenolysis in the liver. This enzyme converts glucose-6-phosphate to glucose, allowing glucose to enter the bloodstream during fasting or low-carbohydrate states.

**Why the Correct Answer is Right**
Glucose-6-phosphatase is exclusively expressed in the liver and kidney and is essential for the final step of gluconeogenesis and glycogenolysis. Its deficiency leads to accumulation of glucose-6-phosphate in hepatocytes, impairing glucose release into the blood. This results in hypoglycemia, hepatomegaly, and elevated blood glucose-6-phosphate levels. The enzyme acts in the final step of the glycogenolysis pathway, where glucose-6-phosphate is dephosphorylated to glucose.

**Why Each Wrong Option is Incorrect**
Option B: Liver phosphorylase deficiency causes type Ia glycogen storage disease, not Von Gierke’s. It affects glycogen breakdown initiation, not glucose-6-phosphate conversion.
Option C: Muscle phosphorylase deficiency leads to McArdle’s disease, characterized by muscle-specific glycogen accumulation and exercise intolerance.
Option D: Debranching enzyme deficiency causes type IV glycogen storage disease, affecting glycogen structure and leading to muscle and liver glycogen accumulation, but not the specific glucose-6-phosphate pathway.

**Clinical Pearl / High-Yield Fact**
Remember: Von Gierke’s disease = **glucose-6-phosphatase deficiency** = **hypoglycemia + hepatomegaly + hyperglycemia with elevated G6P**. It’s the only glycogen storage disease where glucose-6-phosphatase is deficient, and it’s a classic example of impaired gluconeogenesis.

✓ Correct Answer: A. Glucose-6-phosphatase