**Core Concept**
Tarui disease is a rare genetic disorder characterized by a deficiency of the enzyme glycogen phosphorylase, which is crucial for the breakdown of glycogen to glucose in the muscles. This enzyme deficiency leads to impaired glycogenolysis and an accumulation of glycogen in the muscles, resulting in exercise-induced muscle cramps, weakness, and fatigue.

**Why the Correct Answer is Right**
The glycogen phosphorylase enzyme catalyzes the conversion of glycogen to glucose-1-phosphate, which is then converted to glucose-6-phosphate and subsequently released into the bloodstream. In Tarui disease, the deficiency of this enzyme results in reduced glycogen breakdown, leading to muscle cramps and weakness. The liver, which does not rely on glycogen phosphorylase for glycogen breakdown, is not affected in this disease.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify the enzyme involved in Tarui disease. While phosphofructokinase (PFK) is also involved in glycogen metabolism, its deficiency leads to a different disorder, known as McArdle disease.
**Option B:** This option is incorrect because the enzyme alpha-glucosidase is involved in a different disorder, known as Pompe disease, which affects glycogen storage in the lysosomes.
**Option C:** This option is incorrect because the enzyme myophosphorylase is the same as glycogen phosphorylase, but it is not the correct answer because the question specifically asks for the enzyme deficient in Tarui disease.

**Clinical Pearl / High-Yield Fact**
Tarui disease is often confused with McArdle disease, but the two diseases have distinct clinical presentations and enzyme deficiencies. McArdle disease typically presents with exercise-induced muscle cramps and weakness, but also with myoglobinuria, which is not a feature of Tarui disease.

**Correct Answer: C. Glycogen phosphorylase**