Tauri’s disease (phosphofructokinase deficiency) and McArdle disease (myophosphorylase deficiency) are both glycogen storage diseases that affect muscle metabolism, but they involve different enzymes and present with distinct clinical and laboratory features. Here’s how you can differentiate between the two:
Tauri’s Disease (Glycogen Storage Disease Type VII)
- Enzyme Deficiency: Phosphofructokinase (PFK)
- Pathway Affected: Glycolysis, the conversion of fructose-6-phosphate to fructose-1,6-bisphosphate.
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Clinical Presentation:
- Exercise intolerance
- Muscle cramps and pain during exercise
- Myoglobinuria (dark urine after exercise)
- Hemolytic anemia (due to deficient PFK activity in red blood cells)
- Elevated bilirubin and reticulocytes
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Biochemical Findings:
- Increased serum levels of creatine kinase (CK) after exercise.
- Normal to elevated lactate levels during exercise.
- Hemolytic anemia with reticulocytosis.
- Abnormal forearm exercise test: Increased ammonia production with normal to elevated lactate response.
- Genetic Testing: Mutation in the PFKM gene.
McArdle Disease (Glycogen Storage Disease Type V)
- Enzyme Deficiency: Myophosphorylase (muscle glycogen phosphorylase)
- Pathway Affected: Glycogenolysis, the breakdown of glycogen to glucose-1-phosphate in muscle.
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Clinical Presentation:
- Exercise intolerance
- Muscle cramps and pain during exercise
- Myoglobinuria (dark urine after exercise)
- “Second wind” phenomenon (improvement of symptoms after a short rest during exercise)
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Biochemical Findings:
- Elevated serum creatine kinase (CK), especially after exercise.
- Lack of rise in blood lactate levels during exercise (flat lactate response).
- Abnormal forearm exercise test: Little or no increase in lactate with increased ammonia production.
- Genetic Testing: Mutation in the PYGM gene.
Key Differentiating Points
- Enzyme Deficiency:
- Tauri’s Disease: Phosphofructokinase.
- McArdle Disease: Myophosphorylase.
- Hemolytic Anemia:
- Present in Tauri’s Disease (due to PFK deficiency in red blood cells).
- Absent in McArdle Disease.
- Exercise Response:
- Tauri’s Disease: May have a normal to elevated lactate response during exercise.
- McArdle Disease: Flat lactate response during exercise due to inability to break down muscle glycogen.
- Second Wind Phenomenon:
- Present in McArdle Disease.
- Typically absent in Tauri’s Disease.
- Forearm Exercise Test:
- Tauri’s Disease: Increased ammonia production with normal/elevated lactate response.
- McArdle Disease: Increased ammonia production with flat lactate response.
- Genetic Testing:
- Tauri’s Disease: Mutations in PFKM gene.
- McArdle Disease: Mutations in PYGM gene.
These distinctions in clinical presentation, laboratory findings, and genetic testing are crucial for accurately diagnosing and differentiating between Tauri’s disease and McArdle disease.