Glycogen metabolism: glycogen phosphorylase: practice question

A Biochemistry question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Biochemistry · Glycogen metabolism: glycogen phosphorylase

Sample item

A 3-year-old boy has hepatomegaly, growth retardation and mild fasting hypoglycaemia with mild ketosis. Lactate and uric acid are normal, and the storage polymer in the liver is structurally normal. Which enzyme is deficient?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

B. Hepatic glycogen phosphorylase

Hers disease results from deficiency of liver phosphorylase, which blocks release of glucose-1-phosphate from the stored polymer, so the polymer accumulates but is structurally normal. Gluconeogenesis is intact, so hypoglycaemia is mild and lactate and urate are normal. The course is usually benign, and growth often improves by puberty.

Option by option

  • A. Branching enzyme

    Branching enzyme deficiency stores abnormally long-chain polymer and leads to cirrhosis.

  • B. Hepatic glycogen phosphorylase (correct)

    Correct. Absent liver phosphorylase gives hepatomegaly with mild hypoglycaemia and normal lactate and urate.

  • C. Glucose-6-phosphatase

    Glucose-6-phosphatase deficiency causes severe hypoglycaemia, lactic acidosis and hyperuricaemia.

  • D. Debranching enzyme

    Debranching enzyme deficiency stores abnormal short-branched polymer and also affects muscle in many cases.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

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Questions about this Biochemistry question

What is the answer to this Biochemistry question?

The best answer is B, Hepatic glycogen phosphorylase. Hers disease results from deficiency of liver phosphorylase, which blocks release of glucose-1-phosphate from the stored polymer, so the polymer accumulates but is structurally normal.

Why is "Branching enzyme" not the answer?

Branching enzyme deficiency stores abnormally long-chain polymer and leads to cirrhosis.

Why is "Glucose-6-phosphatase" not the answer?

Glucose-6-phosphatase deficiency causes severe hypoglycaemia, lactic acidosis and hyperuricaemia.

Why is "Debranching enzyme" not the answer?

Debranching enzyme deficiency stores abnormal short-branched polymer and also affects muscle in many cases.

What concept does this question test?

It tests Glycogen metabolism: glycogen phosphorylase in Biochemistry. Gluconeogenesis is intact, so hypoglycaemia is mild and lactate and urate are normal. The course is usually benign, and growth often improves by puberty.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Glycogen metabolism: glycogen phosphorylase?

Build one table of enzyme deficiency, disease, inheritance and key finding, then revise it by spaced recall. Then use the flashcards and the other Biochemistry questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.