Learning Objectives
- Differentiate between the clinical presentations of Von Gierke, Pompe, Cori, Andersen, and McArdle diseases.
- Identify the deficient enzymes and the specific metabolic pathways affected in each type.
- Distinguish between Type I and Type III using blood lactate levels.
- Understand the importance of PAS staining in diagnosing glycogen accumulation.
1. Overview of Glycogen Storage Diseases (GSD)
These are a group of inherited disorders that result in abnormal glycogen metabolism. This leads to an accumulation of glycogen within cells, which can be visualized using a Periodic acid–Schiff (PAS) stain.
High-Yield Mnemonics:
- ABCD: Andersen = Branching; Cori = Debranching.
- “Vice President Can’t Accept Money”: Von Gierke, Pompe, Cori, Andersen, McArdle.
2. Clinical Comparison Table
| Disease (Type) | Deficient Enzyme | Key Clinical Findings | Metabolic Clues |
|---|---|---|---|
| Von Gierke (Type I) | Glucose-6-phosphatase | Severe fasting hypoglycemia, hepatomegaly, “doll-like” face. | ↑↑ Lactate, ↑ Uric acid (Gout), ↑ Triglycerides. |
| Pompe (Type II) | Acid α-1,4-glucosidase (Acid Maltase) | Cardiomyopathy, enlarged tongue, hypotonia, and early death. | Lysosomal accumulation. “Pompe trashes the Pump (Heart).” |
| Cori (Type III) | Debranching enzymes | Milder Von Gierke symptoms, hepatomegaly. | Normal lactate levels. Accumulation of Limit Dextrins. |
| Andersen (Type IV) | Branching enzyme | Hepatosplenomegaly, failure to thrive, infantile cirrhosis. | Abnormal glycogen with few branch points. |
| McArdle (Type V) | Myophosphorylase (Muscle glycogen phosphorylase) | Painful muscle cramps, myoglobinuria (red urine) after exercise. | Flat venous lactate curve during exercise. “McArdle = Muscle” |
Activity: GSD Enzyme Challenge
3. Deep Dive into Specific Pathologies
- Von Gierke Management: Avoid fructose and galactose because they cannot be converted to glucose and will instead worsen lactic acidosis and hyperuricemia.
- McArdle’s Second Wind: During exercise, increased blood flow eventually brings enough blood-borne glucose and free fatty acids to the muscle to bypass the need for glycogenolysis, resulting in decreased pain.
- Cori vs. Von Gierke: The most important lab difference is that in Cori Disease, gluconeogenesis is intact, which is why lactate levels remain normal, and symptoms are generally milder.
Activity: Clinical Vignette Quiz
Memory Hook:
Type I: Liver/Kidney (G for Gout/Glucose).
Type II: Heart/Pump (Pompe).
Type III: Debranching (Cori).
Type IV: Branching (Andersen).
Type V: Muscle (McArdle).