Q: About glycogen phosphorylase deficiency (CM-02)

In the study of a 14 year-old male patient who you suspect has a deficiency of muscle glycogen phosphorylase, you indicate a test based in exercising his forearm by squeezing a rubber ball. Compared with the normal person performing the same exercise, this patient would exhibit which of the following?


a)     Exercise for a longer time without fatigue

b)      increased glucose levels in blood drawn from his forearm

c)      decreased lactate levels in blood drawn from his forearm

d)     lower levels of glycogen in biopsy specimens from his forearm muscle

e)     Hyperglycemia

f)       Hypoglycemia










3 thoughts on “Q: About glycogen phosphorylase deficiency (CM-02)

  1. Pingback: About Muscle Glycogen Phosphorylase Deficiency (GSD V) « The Biochemistry Questions Site

  2. The answer is (c).
    For releasing glucose from glycogen from the cells to the blood, it is necesssary to convert the glucose 6 (P)released from glycogen to glucose. Muscular tissue does not have glucose 6 phosphatase,(the enzyme necessary for this conversion). This enzyme is present in the liver, that is why the glycogen in the liver can be used for mantaining glucose levels, but glycogen in muscle can not be used for this purpose. The bottom line is that normally while the glycogen stored in the liver is used for storing glucose that can be used for redistribution through blood to other tissues, the glycogen in the muscle act as a storage of glucose that can be used only by the muscular tissue for energetic purposes, since the glucose 6 (P) formed can not be released to blood, but continue through glycosylisis in the muscular tissue.
    This patient has a lack of Glycogen phosphorylase in the muscle (GSD Type V or Mc Ardle disease). Since the carbohydrate metabolism in the liver is not affected, hypoglycemia is not a characteristic in this patient.

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