**Core Concept**
Muscle phosphorylase deficiency is a condition where the enzyme responsible for breaking down glycogen to glucose in muscles is impaired. This leads to an accumulation of glycogen in muscle cells, causing a glycogen storage disorder. The underlying principle is a deficiency in a key enzyme in glycogenolysis.

**Why the Correct Answer is Right**
Muscle phosphorylase is an enzyme that catalyzes the phosphorolytic breakdown of glycogen to glucose-1-phosphate in muscle cells. In muscle phosphorylase deficiency, the enzyme is either absent or has reduced activity, leading to an accumulation of glycogen in muscles. This accumulation can cause muscle cramps, weakness, and fatigue due to the impaired ability to break down glycogen to glucose for energy production.

**Why Each Wrong Option is Incorrect**
* **Option A:** Glycogen storage disorder due to debranching enzyme deficiency is known as Cori's disease or debranching enzyme deficiency. This is a different enzyme involved in glycogenolysis.
* **Option B:** McArdle's disease, also known as muscle glycogen storage disease type V, is caused by a deficiency of muscle phosphorylase. This option is correct.
* **Option C:** Pompe disease is caused by a deficiency of acid alpha-glucosidase, an enzyme involved in glycogen breakdown in lysosomes. This is a different enzyme and disorder.
* **Option D:** Hers' disease is caused by a deficiency of liver phosphorylase kinase, an enzyme involved in glycogenolysis in the liver. This is a different enzyme and disorder.

**Clinical Pearl / High-Yield Fact**
Remember that glycogen storage disorders can be classified into two main categories: those affecting glycogenolysis (e.g., McArdle's disease) and those affecting glycogen synthesis (e.g., Hers' disease).

**Correct Answer: B. McArdle's disease, also known as muscle glycogen storage disease type V, is caused by a deficiency of muscle phosphorylase.**