**Core Concept**
Pompe's disease is a rare genetic disorder caused by a deficiency of acid alpha-glucosidase (GAA) enzyme, leading to accumulation of glycogen in lysosomes. This results in cellular damage and organ dysfunction, primarily affecting the heart, muscles, and nervous system.

**Why the Correct Answer is Right**
The GAA enzyme plays a crucial role in breaking down glycogen into glucose within lysosomes. Without sufficient GAA enzyme, glycogen accumulates, causing cellular damage and triggering a cascade of downstream effects. Specifically, the deficiency affects the lysosomal acid alpha-glucosidase activity, which is necessary for glycogen breakdown. This leads to severe consequences, including muscle weakness, cardiomegaly, and respiratory failure.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because Pompe's disease is not caused by a deficiency of acid maltase, which is a different enzyme involved in carbohydrate metabolism.
**Option B:** This option is incorrect because Fabry disease is caused by a deficiency of alpha-Gal A enzyme, not acid alpha-glucosidase.
**Option C:** This option is incorrect because Gaucher disease is caused by a deficiency of glucocerebrosidase enzyme, not acid alpha-glucosidase.

**Clinical Pearl / High-Yield Fact**
Pompe's disease is an autosomal recessive disorder, meaning that a child must inherit two defective GAA genes (one from each parent) to develop the disease. This genetic inheritance pattern is essential to remember when diagnosing and managing Pompe's disease.

**Correct Answer: C. Acid alpha-glucosidase (GAA) enzyme**