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A child presents with low blood glucose (hypoglycemia), enlarged liver (hepatomegaly), and excess fat deposition in the cheeks (cherubic facies). A liver biopsy reveals excess glycogen in hepatocytes. Deficiency of which of the following enzymes might explain this phenotype?
Options:
1. α-1,1-glucosidase
2. α-1,1-galactosidase
3. α-1,4-glucosidase
4. α-1,4-galactosidase
5. α-1,6-galactosidase
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The Correct Answer is: α-1,4-glucosidase
Explanation:
The child has symptoms of glycogen storage disease. Glycogen is a glucose polymer with linear regions linked through the C1 aldehyde of one glucose to the C4 alcohol of the next (α-1,4-glucoside linkage). There are also branches from the linear glycogen polymer that have α-1,6-glucoside linkages. Glycogen is synthesized during times of carbohydrate and energy surplus, but must be degraded during fasting to provide energy. Separate enzymes for breakdown include phosphylases (α-1,4-glucosidases) that cleave linear regions of glycogen and debranching enzymes (α-1,6-glucosidases) that cleave branch points. Glucose-6-phosphatase is needed in the liver to liberate free glucose from glucose-6-phosphate, providing fuel for other organs. There is no glucose- 6-phosphatase in muscle, and muscle glycogenolysis provides energy just for muscle with production of lactate. Deficiencies of more than eight enzymes involved in glycogenolysis, including those mentioned, can produce glycogen storage disease.
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have pity on me kooooola!
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a-1,4-glucosidase...Pompe's disease...is not it cardiomegaly without hypoglycemia since it is not in normal process of glycogenolysis? Thanks to correct me!
