Biomolecules and enzymes: Morquio syndrome: 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 · Biomolecules and enzymes: Morquio syndrome

Sample item

A 6-year-old child has a short trunk, pectus carinatum, knock knees, odontoid hypoplasia and normal intelligence. Urine contains excess keratan sulfate. Which enzyme is deficient?

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

The answer and the reasoning

D. N-acetylgalactosamine-6-sulfatase

Morquio syndrome (MPS IV) is caused by deficiency of N-acetylgalactosamine-6-sulfatase, which degrades keratan sulfate and chondroitin 6-sulfate. Skeletal dysplasia with odontoid hypoplasia and preserved intelligence is the typical picture.

Option by option

  • A. Beta-glucuronidase

    Beta-glucuronidase deficiency causes Sly syndrome, a rare disorder with excess dermatan, heparan and chondroitin sulfates.

  • B. Iduronate-2-sulfatase

    Iduronate-2-sulfatase deficiency causes Hunter syndrome, with dermatan and heparan sulfate in urine.

  • C. Arylsulfatase B

    Arylsulfatase B deficiency causes Maroteaux-Lamy syndrome, with dermatan sulfate excretion and normal intelligence but no keratan sulfate excess.

  • D. N-acetylgalactosamine-6-sulfatase (correct)

    Correct. This enzyme degrades keratan sulfate, and its loss gives skeletal dysplasia with normal intelligence.

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, N-acetylgalactosamine-6-sulfatase. Morquio syndrome (MPS IV) is caused by deficiency of N-acetylgalactosamine-6-sulfatase, which degrades keratan sulfate and chondroitin 6-sulfate.

Why is "Beta-glucuronidase" not the answer?

Beta-glucuronidase deficiency causes Sly syndrome, a rare disorder with excess dermatan, heparan and chondroitin sulfates.

Why is "Iduronate-2-sulfatase" not the answer?

Iduronate-2-sulfatase deficiency causes Hunter syndrome, with dermatan and heparan sulfate in urine.

Why is "Arylsulfatase B" not the answer?

Arylsulfatase B deficiency causes Maroteaux-Lamy syndrome, with dermatan sulfate excretion and normal intelligence but no keratan sulfate excess.

What concept does this question test?

It tests Biomolecules and enzymes: Morquio syndrome in Biochemistry. Skeletal dysplasia with odontoid hypoplasia and preserved intelligence is the typical picture.

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 Biomolecules and enzymes: Morquio syndrome?

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.