Glycogen storage disorders: Cori disease: 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 storage disorders: Cori disease

Sample item

A 2-year-old boy has hepatomegaly, fasting hypoglycaemia and ketosis, with raised transaminases and creatine kinase. His plasma lactate and uric acid are normal, and a glucagon test after a meal raises glucose but fails after an overnight fast. Which explanation best accounts for the normal lactate and uric acid?

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

The answer and the reasoning

D. Glucose-6-phosphatase and gluconeogenesis are intact, and only glucose from outer branch points is not released

In GSD type III (Cori or Forbes disease) the debranching enzyme is deficient, producing abnormal glycogen with short outer chains (limit dextrin). Glucose-6-phosphatase is normal, so gluconeogenesis supplies glucose and there is no lactic acidosis or hyperuricaemia as seen in type I. The glucagon response is blunted when fasting because glycogen cannot be fully mobilised.

Option by option

  • A. Glucose-6-phosphatase is absent but lactate is cleared by the Cori cycle

    Absent G6Pase defines type I disease, in which lactate and uric acid are raised despite the Cori cycle.

  • B. Gluconeogenesis is intact because glycogen synthase is overactive

    Glycogen synthase does not drive gluconeogenesis, and overactivity would not explain the findings.

  • C. Hepatic glucose-6-phosphate is shunted into the pentose phosphate pathway

    Shunting to the pentose phosphate pathway is a feature of type I disease and does not explain normal lactate here.

  • D. Glucose-6-phosphatase and gluconeogenesis are intact, and only glucose from outer branch points is not released (correct)

    Correct. Intact G6Pase and gluconeogenesis spare lactate and uric acid; only the branch-point glucose release is blocked.

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 D, Glucose-6-phosphatase and gluconeogenesis are intact, and only glucose from outer branch points is not released. In GSD type III (Cori or Forbes disease) the debranching enzyme is deficient, producing abnormal glycogen with short outer chains (limit dextrin).

Why is "Glucose-6-phosphatase is absent but lactate is cleared by the Cori cy…" not the answer?

Absent G6Pase defines type I disease, in which lactate and uric acid are raised despite the Cori cycle.

Why is "Gluconeogenesis is intact because glycogen synthase is overactive" not the answer?

Glycogen synthase does not drive gluconeogenesis, and overactivity would not explain the findings.

Why is "Hepatic glucose-6-phosphate is shunted into the pentose phosphate pat…" not the answer?

Shunting to the pentose phosphate pathway is a feature of type I disease and does not explain normal lactate here.

What concept does this question test?

It tests Glycogen storage disorders: Cori disease in Biochemistry. Glucose-6-phosphatase is normal, so gluconeogenesis supplies glucose and there is no lactic acidosis or hyperuricaemia as seen in type I. The glucagon response is blunted when fasting because glycogen cannot be fully mobilised.

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 storage disorders: Cori disease?

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.