Mc Ardle’s disease is due to deficiency of?
**Core Concept**
McArdle's disease, also known as Glycogen storage disease type V, is a rare genetic disorder characterized by the inability to break down glycogen into glucose for energy production in muscles. This condition is caused by a deficiency of a specific enzyme that plays a crucial role in glycogenolysis.
**Why the Correct Answer is Right**
The correct answer is due to the deficiency of myophosphorylase, an enzyme responsible for the first step in glycogenolysis. Myophosphorylase catalyzes the conversion of glycogen to glucose-1-phosphate, which is then converted to glucose-6-phosphate and eventually enters the glycolytic pathway to produce energy. Without sufficient myophosphorylase, glycogen accumulates in muscles, leading to muscle cramps, weakness, and fatigue.
**Why Each Wrong Option is Incorrect**
* **Option A:** Hexokinase is an enzyme involved in the first step of glycolysis, where glucose is converted to glucose-6-phosphate. While it is an important enzyme in glucose metabolism, its deficiency does not lead to McArdle's disease.
* **Option B:** Phosphofructokinase is another enzyme in the glycolytic pathway, involved in the conversion of fructose-6-phosphate to fructose-1,6-bisphosphate. Its deficiency leads to a different condition, glycogen storage disease type VII.
* **Option C:** Pyruvate kinase is the final enzyme in the glycolytic pathway, responsible for the conversion of phosphoenolpyruvate to pyruvate. While its deficiency can lead to muscle weakness and fatigue, it is not associated with McArdle's disease.
**Clinical Pearl / High-Yield Fact**
McArdle's disease is an autosomal recessive disorder, meaning that affected individuals inherit two copies of the mutated gene, one from each parent. Early diagnosis and management are crucial to prevent muscle damage and improve quality of life.
**Correct Answer:** C. Phosphorylase deficiency is not correct, the correct answer is actually **myophosphorylase**.