Comprehensive Review of McArdle Disease (Type V): A Q&A Format Study Guide

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Question: What is McArdle disease?
Answer: McArdle disease is a type of genetic disorder affecting muscle metabolism.Question: What are the findings of McArdle disease (type V)?
Answer: McArdle disease (type V) is characterized by an increase in glycogen in muscle, but muscle cannot break it down. Symptoms include painful muscle cramps, myoglobinuria (red urine) with strenuous exercise, and arrhythmia from electrolyte abnormalities. A second-wind phenomenon is noted during exercise due to increased muscular blood flow.Question: What is the deficient enzyme in McArdle disease (type V)?
Answer: The deficient enzyme in McArdle disease (type V) is skeletal muscle glycogen phosphorylase (myophosphorylase).Question: What is the characteristic of McArdle disease (type V) during exercise?
Answer: During exercise, McArdle disease (type V) is characterized by a flat venous lactate curve with a normal rise in ammonia levels.Question: Are blood glucose levels affected in McArdle disease (type V)?
Answer: Blood glucose levels are typically unaffected in McArdle disease (type V).Question: What does McArdle mean?
Answer: McArdle means muscle. Question: What is the main symptom of McArdle disease (type V)?
Answer: The main symptom of McArdle disease (type V) is painful muscle cramps during strenuous exercise.Question: What is the result of the increase in glycogen in muscle in McArdle disease (type V)?
Answer: The result of the increase in glycogen in muscle in McArdle disease (type V) is that the muscle cannot break it down, leading to painful muscle cramps and myoglobinuria (red urine).Question: What is the significance of the second-wind phenomenon in McArdle disease (type V)?
Answer: The second-wind phenomenon in McArdle disease (type V) is significant because it is a notable symptom during exercise, due to increased muscular blood flow.Question: What is the effect of McArdle disease (type V) on lactate levels during exercise?
Answer: McArdle disease (type V) results in a flat venous lactate curve during exercise.Question: What is the effect of McArdle disease (type V) on ammonia levels during exercise?
Answer: McArdle disease (type V) results in a normal rise in ammonia levels during exercise. Question: How does McArdle disease (type V) affect the muscle?
Answer: McArdle disease (type V) affects the muscle by causing an increase in glycogen, but the muscle cannot break it down, leading to painful muscle cramps and myoglobinuria (red urine).Question: What is the significance of myoglobinuria in McArdle disease (type V)?
Answer: Myoglobinuria is significant in McArdle disease (type V) because it is a symptom of the disease, occurring during strenuous exercise and resulting in red urine.Question: How does McArdle disease (type V) cause arrhythmia?
Answer: McArdle disease (type V) causes arrhythmia due to electrolyte abnormalities.Question: How does McArdle disease (type V) affect electrolyte levels?
Answer: McArdle disease (type V) affects electrolyte levels by causing abnormalities, which can lead to arrhythmia.Question: Why is the venous lactate curve flat in McArdle disease (type V)?
Answer: The venous lactate curve is flat in McArdle disease (type V) due to the deficiency of skeletal muscle glycogen phosphorylase (myophosphorylase).tab

[@KittysAreCute]

McArdle does not mean “muscle”. The disease was named after Dr. Brian McArdle. The second wind phenomenon has more to do with fatty acid metabolism than increased blood flow.

[@ianmacdougall2467]

Red urine from myoglobinuria is not a symptom of the disease, it is a rare effect of over exertion. Most patients do not experience it often.