Andersen disease is due to lack of: March 2007
**Core Concept**
Andersen disease, also known as glycogen storage disease type IV, is a rare genetic disorder characterized by the accumulation of glycogen in the liver and other organs. It is caused by a deficiency of a key enzyme involved in glycogen breakdown.
**Why the Correct Answer is Right**
The correct answer is due to a deficiency of brancher enzyme, also known as 1,4-alpha-glucan branching enzyme. This enzyme is responsible for branching glycogen chains, allowing them to be broken down and utilized by the body. Without this enzyme, glycogen accumulates in the liver and other organs, leading to the symptoms of Andersen disease. The deficiency of brancher enzyme results in the formation of a unique type of glycogen known as amylopectin, which is resistant to breakdown.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify the correct enzyme involved in Andersen disease. While glycogen synthase is an enzyme involved in glycogen metabolism, it is not the enzyme deficient in Andersen disease.
**Option B:** This option is incorrect because it is a different enzyme involved in glycogen metabolism. Debranching enzyme is involved in glycogen breakdown, but its deficiency leads to a different glycogen storage disease, known as Cori disease.
**Option C:** This option is incorrect because it is not a specific enzyme involved in glycogen metabolism. Glycogen phosphorylase is an enzyme involved in glycogen breakdown, but its deficiency leads to a different glycogen storage disease, known as Hers disease.
**Clinical Pearl / High-Yield Fact**
Andersen disease is a rare genetic disorder that highlights the importance of enzyme function in glycogen metabolism. It is essential to remember that different enzymes involved in glycogen metabolism lead to distinct glycogen storage diseases with different clinical presentations.
**Correct Answer:** B. Debranching enzyme.