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CASE FILES: BIOCHEMISTRY
C O M P R E H E N SIO N Q U E ST IO N S
For Questions [20.1] and [20.2] refer to the following case:
A female infant appeared normal at birth but developed signs of liver disease
and muscular weakness at 3 months. She had periods of hypoglycemia, par-
ticularly on awakening. Examination revealed an enlarged liver. Laboratory
analyses following fasting revealed ketoacidosis, blood pH 7.25, and eleva-
tions in both alanine transaminase (ALT) and aspartate transaminase (AST).
Administration of glucagon following a carbohydrate meal elicited a normal
rise in blood glucose, but glucose levels did not rise when glucagon was
administered following an overnight fast. Liver biopsy revealed an increase in
the glycogen content (6 percent of wet weight).
[20.1] In which of the following enzymes is a genetic deficiency most likely
for this patient?
A. Branching enzyme
B. Debranching enzyme
C. Glucose-6-phosphatase
D. Glycogen synthase
E. Muscle phosphorylase
[20.2] To prevent the frequent episodes of hypoglycemia, which of the fol-
lowing dietary supplements would be most appropriate for this patient?
A. Casein (milk protein)
B. Fish oil
C. Fructose
D. Lactose
E. Uncooked cornstarch
[20.3] A 17-year-old male presents complaining of an inability to perform
strenuous exercise without bringing on painful muscle cramps and
weakness. He indicated that mild to moderate exercise resulted in no
problems. When he was administered an ischemic exercise test, his
serum lactate concentrations did not increase significantly. A defi-
ciency in which of the following enzymes is most likely the cause of
the patient’s muscle cramps?
A. Carnitine palmitoyl transferase II
B. Glucose-6-phosphatase
C. Glycogen phosphorylase
D. Glycogen synthase
E. Very long chain acyl-CoA dehydrogenase
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