**Core Concept:** Pompe's disease is a rare genetic disorder caused by deficiency in acid alpha-glucosidase enzyme (GAA), which leads to lysosomal glycogen accumulation in various tissues, particularly the heart and skeletal muscles.

**Why the Correct Answer is Right:**
Pompe's disease is an example of a lysosomal storage disorder, where the deficiency in GAA enzyme results in the accumulation of glycogen in lysosomes. This leads to cellular dysfunction and damage, particularly in the heart and skeletal muscles. The correct answer, D, is the deficiency of GAA enzyme, which is responsible for breaking down glycogen and preventing its accumulation.

**Why Each Wrong Option is Incorrect:**
A) Option A, deficiency of another enzyme (e.g., LDH or CK), is unrelated to the pathogenesis of Pompe's disease.
B) Option B, increased glycogen synthesis, actually exacerbates the disease by worsening glycogen accumulation.
C) Option C, increased glycogen breakdown, would not address the deficiency of GAA enzyme and thus is irrelevant.

**Clinical Pearl / High-Yield Fact:**
Pompe's disease is classified as a type II glycogen storage disease, as it primarily affects infants and can cause severe cardiomyopathy and respiratory distress. Treatment options include enzyme replacement therapy and gene therapy, which aim to restore GAA enzyme function and reduce glycogen accumulation.

**Correct Answer:** D) Deficiency of GAA enzyme (acid alpha-glucosidase).