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

**Why the Correct Answer is Right**
Pompe's disease is characterized by the accumulation of glycogen in lysosomes due to the deficiency of the acid alpha-glucosidase (GAA) enzyme. This accumulation leads to cellular dysfunction and eventually results in the clinical manifestations of the disease. The disease is classified into six types based on the age of onset and the severity of symptoms.

**Why Each Wrong Option is Incorrect**
**Option A:** Glycogen storage disease type II, which is the correct term for Pompe's disease. This option is incorrect because it is a synonym for Pompe's disease.
**Option B:** Accumulation of glycogen in lysosomes is indeed a feature of Pompe's disease. This option is incorrect because it is a characteristic of the disease, not an exception.
**Option C:** Hypotonia, muscle weakness, and cardiomegaly are all features of Pompe's disease. This option is incorrect because it describes common symptoms of the disease, not an exception.

**Clinical Pearl / High-Yield Fact**
Pompe's disease is often referred to as the "lysosomal glycogen storage disease" due to the accumulation of glycogen in lysosomes.

**Correct Answer:** A. Glycogen storage disease type II.