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 3-year-old child has hepatomegaly and fasting hypoglycaemia with ketosis. Lactate and uric acid are normal. Transaminases and creatine kinase are raised, and liver biopsy shows glycogen with abnormally short outer branches (limit dextrin-like). Which enzyme is deficient?

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

The answer and the reasoning

D. Amylo-1,6-glucosidase (debranching enzyme)

In type III glycogenosis the debranching enzyme is absent, so phosphorylase stops four residues from a branch point and limit dextrin accumulates. Gluconeogenesis and the glucose-6-phosphatase step are intact, so hypoglycaemia is milder than in type I, with normal lactate and uric acid. Muscle involvement raises creatine kinase.

Option by option

  • A. Glucose-6-phosphatase

    Glucose-6-phosphatase deficiency produces lactic acidosis and hyperuricaemia, and the glycogen structure is normal.

  • B. Glycogen branching enzyme

    Branching enzyme deficiency gives long unbranched glycogen chains and cirrhosis, not short outer branches.

  • C. Lysosomal acid alpha-glucosidase

    Acid alpha-glucosidase deficiency causes lysosomal storage with cardiomyopathy and no hypoglycaemia.

  • D. Amylo-1,6-glucosidase (debranching enzyme) (correct)

    Failure to remove branches gives limit dextrin, with intact gluconeogenesis explaining normal lactate and uric acid.

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, Amylo-1,6-glucosidase (debranching enzyme). In type III glycogenosis the debranching enzyme is absent, so phosphorylase stops four residues from a branch point and limit dextrin accumulates.

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

Glucose-6-phosphatase deficiency produces lactic acidosis and hyperuricaemia, and the glycogen structure is normal.

Why is "Glycogen branching enzyme" not the answer?

Branching enzyme deficiency gives long unbranched glycogen chains and cirrhosis, not short outer branches.

Why is "Lysosomal acid alpha-glucosidase" not the answer?

Acid alpha-glucosidase deficiency causes lysosomal storage with cardiomyopathy and no hypoglycaemia.

What concept does this question test?

It tests Glycogen storage disorders: Cori disease in Biochemistry. Gluconeogenesis and the glucose-6-phosphatase step are intact, so hypoglycaemia is milder than in type I, with normal lactate and uric acid. Muscle involvement raises creatine kinase.

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.