Glycogen storage disorders: Pompe 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: Pompe disease

Sample item

A 4-month-old infant is hypotonic with feeding difficulty, macroglossia, a markedly enlarged heart and a short PR interval on ECG. Blood glucose is normal. Which enzyme is deficient?

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

The answer and the reasoning

C. Lysosomal acid alpha-1,4-glucosidase

Pompe disease (type II glycogenosis) is a lysosomal storage disorder in which acid maltase deficiency causes glycogen accumulation within lysosomes of cardiac and skeletal muscle. Infants have cardiomegaly, hypotonia and macroglossia without hypoglycaemia. Enzyme replacement therapy with alglucosidase alfa improves survival.

Option by option

  • A. Glycogen branching enzyme

    Branching enzyme deficiency causes progressive liver cirrhosis with abnormal long-chain glycogen.

  • B. Muscle glycogen phosphorylase

    Muscle phosphorylase deficiency causes exercise cramps in adolescents and adults, not infantile cardiomegaly.

  • C. Lysosomal acid alpha-1,4-glucosidase (correct)

    Lysosomal glycogen build-up in heart and muscle explains the cardiomyopathy and floppy infant with normal glucose.

  • D. Glucose-6-phosphatase

    Glucose-6-phosphatase deficiency causes fasting hypoglycaemia, hepatomegaly and lactic acidosis.

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 C, Lysosomal acid alpha-1,4-glucosidase. Pompe disease (type II glycogenosis) is a lysosomal storage disorder in which acid maltase deficiency causes glycogen accumulation within lysosomes of cardiac and skeletal muscle.

Why is "Glycogen branching enzyme" not the answer?

Branching enzyme deficiency causes progressive liver cirrhosis with abnormal long-chain glycogen.

Why is "Muscle glycogen phosphorylase" not the answer?

Muscle phosphorylase deficiency causes exercise cramps in adolescents and adults, not infantile cardiomegaly.

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

Glucose-6-phosphatase deficiency causes fasting hypoglycaemia, hepatomegaly and lactic acidosis.

What concept does this question test?

It tests Glycogen storage disorders: Pompe disease in Biochemistry. Infants have cardiomegaly, hypotonia and macroglossia without hypoglycaemia. Enzyme replacement therapy with alglucosidase alfa improves survival.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. 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: Pompe 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.