Strenuous exercise is not done in this glycogen storage disease:
**Core Concept**
Glycogen storage diseases (GSDs) are a group of inherited disorders affecting glycogen metabolism. Strenuous exercise requires a significant increase in energy supply, which is usually met by glycogen breakdown in muscles. Certain GSDs are characterized by the inability to mobilize glycogen due to enzyme deficiencies, making strenuous exercise contraindicated in these conditions.
**Why the Correct Answer is Right**
The correct answer is related to McArdle's disease (GSD type V), which is caused by a deficiency of the enzyme myophosphorylase. Myophosphorylase is essential for the breakdown of glycogen to glucose-1-phosphate, which is then converted to glucose-6-phosphate and eventually enters the glycolytic pathway to produce energy. In McArdle's disease, strenuous exercise cannot be sustained because glycogen cannot be broken down to meet the energy demands of the muscles.
**Why Each Wrong Option is Incorrect**
**Option A:** Pompe disease (GSD type II) is caused by a deficiency of acid alpha-glucosidase (also known as acid maltase), which breaks down glycogen in lysosomes. While Pompe disease does result in glycogen accumulation, the enzyme deficiency primarily affects glycogen breakdown in lysosomes, not glycogen mobilization in muscles.
**Option B:** Cori disease (GSD type III) is caused by a deficiency of the debranching enzyme amylo-alpha-1,6-glucosidase. This enzyme deficiency affects glycogen breakdown, but not as severely as in McArdle's disease, and patients with Cori disease may still be able to perform strenuous exercise.
**Option C:** Hers disease (GSD type VI) is caused by a deficiency of liver phosphorylase. While this enzyme deficiency affects glycogen breakdown in the liver, patients with Hers disease may still be able to mobilize glycogen in muscles to meet energy demands.
**Option D:** None of the above is incorrect, as the question asks for the glycogen storage disease in which strenuous exercise is not done.
**Clinical Pearl / High-Yield Fact**
McArdle's disease is characterized by exercise-induced muscle cramps, weakness, and fatigue. Patients with McArdle's disease may also experience myoglobinuria (the presence of myoglobin in the urine), which can indicate muscle damage.
**Correct Answer:** A. McArdle's disease.