Question

Andersen's disease (glycogen storage disease type IV) is a condition characterized by a deficiency in glycogen branching enzyme. Absence of this enzyme would be likely to cause all of the following effects EXCEPT: (A) decreased glycogen solubility in human cells. (B) slower action of glycogen phosphorylase. (C) less storage of glucose in the body. (D) glycogen devoid of \(\alpha-1,4\) linkages.

Short answer

(D) glycogen devoid of \(\alpha-1,4\) linkages.

Step-by-step solution

- Understand the Disease

Andersen's disease (glycogen storage disease type IV) is caused by a deficiency in the glycogen branching enzyme, which is responsible for creating \(\alpha-1,6\) linkages in glycogen.

- Identify the Effects of Enzyme Deficiency

Without this enzyme, glycogen molecules will be less branched, leading to decreased solubility and potentially slower mobilization (breakdown) since glycogen phosphorylase works on branching points.

- Evaluate the Options

Consider each option: (A) Decreased glycogen solubility - true due to less branching. (B) Slower action of glycogen phosphorylase - true as it acts on branch points. (C) Less storage of glucose - true since inefficient storage. (D) Glycogen devoid of \(\alpha-1,4\) linkages - false because \(\alpha-1,4\) linkages are still formed, the deficiency is in the branching enzyme (which affects \(\alpha-1,6\) linkages).

Key concepts

Glycogen Storage Diseases

Glycogen storage diseases (GSDs) are a group of inherited genetic conditions that affect the body's ability to store and use glycogen properly. Glycogen is the stored form of glucose, a key energy source in the body. There are several types of GSDs, each resulting from a deficiency in a specific enzyme. These enzymes are crucial for the metabolism of glycogen.

For instance, Andersen's disease, also known as glycogen storage disease type IV, stems from a deficiency in the glycogen branching enzyme. This specific enzyme is responsible for adding branches to the glycogen molecule. Without proper enzyme function, glycogen becomes poorly branched and insoluble.

Symptoms can vary depending on the type of GSD but often include muscle pain, fatigue, an enlarged liver, and hypoglycemia. Managing glycogen storage diseases typically involves a specialized diet and, in some cases, medication to manage symptoms.

Enzyme Deficiency

Enzymes are special proteins that catalyze, or speed up, biochemical reactions. In the context of glycogen metabolism, enzymes play a crucial role in both the synthesis and breakdown of glycogen. A deficiency in any of these specific enzymes can lead to a glycogen storage disease.

In Andersen's disease, the deficiency is in the glycogen branching enzyme. This enzyme's absence disrupts the natural process of creating \(\alpha-1,6\) linkages in glycogen, leading to poorly branched, insoluble glycogen. This abnormal glycogen cannot be mobilized effectively, making it difficult for the body to access stored glucose when needed.

Such enzyme deficiencies often result from genetic mutations. In the case of Andersen's disease, the mutation affects the gene responsible for producing the branching enzyme, leading to its reduced activity or complete absence. Understanding these genetic causes can help in developing targeted therapies and treatments for affected individuals.

Glycogen Structure

Glycogen is a highly branched polysaccharide, primarily composed of glucose units linked together. Its structure is crucial for its function as a quickly accessible energy reserve.

Glycogen's structure consists of a core protein called glycogenin, surrounded by chains of glucose molecules. These glucose chains are connected by two types of linkages:

• \(\alpha-1,4\) linkages: These form the linear, straight chains of glucose.
• \(\alpha-1,6\) linkages: These create the branching points in the glycogen molecule.

In Andersen's disease, the deficiency in the glycogen branching enzyme means fewer \(\alpha-1,6\) linkages. This results in less branched, less soluble glycogen, which cannot be broken down as efficiently. This inefficient structure can cause various health problems since the body struggles to release glucose rapidly during high energy demand situations.

Alpha Linkages

Alpha linkages are the types of bonds that bind the glucose molecules together in glycogen. There are two primary types of alpha linkages in glycogen:

• \(\alpha-1,4\) linkages: These connect the glucose units in a linear fashion. They are the most common type of linkage in glycogen and provide the foundation for the molecule's structure.
• \(\alpha-1,6\) linkages: These occur at branching points, allowing glycogen to take on a more compact and branched structure. Branching is essential for making glycogen soluble and readily accessible for energy release.

In the context of Andersen's disease, the problem lies in the creation of \(\alpha-1,6\) linkages. The deficiency in the branching enzyme means that while \(\alpha-1,4\) linkages can still form, the crucial branching points (\