Glycosaminoglycans: mucopolysaccharidosis: 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 · Glycosaminoglycans: mucopolysaccharidosis

Sample item

An 18-month-old boy has coarse facies, corneal clouding, hepatosplenomegaly, a gibbus and regression of milestones. Urine contains excess dermatan sulfate and heparan sulfate. Which enzyme is deficient?

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

The answer and the reasoning

C. Alpha-L-iduronidase

Hurler syndrome (MPS I) is caused by alpha-L-iduronidase deficiency, so dermatan and heparan sulfate accumulate in lysosomes. Corneal clouding distinguishes it from Hunter syndrome. Treatment options include haematopoietic stem cell transplantation in early disease and enzyme replacement.

Option by option

  • A. Iduronate-2-sulfatase

    Iduronate-2-sulfatase deficiency causes X-linked Hunter syndrome, which has clear corneas.

  • B. Heparan N-sulfatase

    Heparan N-sulfatase deficiency causes Sanfilippo A, dominated by severe neurological decline with only heparan sulfate excess.

  • C. Alpha-L-iduronidase (correct)

    Correct. Alpha-L-iduronidase deficiency with corneal clouding is Hurler syndrome.

  • D. N-acetylgalactosamine-6-sulfatase

    N-acetylgalactosamine-6-sulfatase deficiency causes Morquio A, with keratan sulfate excess and skeletal dysplasia.

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, Alpha-L-iduronidase. Hurler syndrome (MPS I) is caused by alpha-L-iduronidase deficiency, so dermatan and heparan sulfate accumulate in lysosomes.

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

Iduronate-2-sulfatase deficiency causes X-linked Hunter syndrome, which has clear corneas.

Why is "Heparan N-sulfatase" not the answer?

Heparan N-sulfatase deficiency causes Sanfilippo A, dominated by severe neurological decline with only heparan sulfate excess.

Why is "N-acetylgalactosamine-6-sulfatase" not the answer?

N-acetylgalactosamine-6-sulfatase deficiency causes Morquio A, with keratan sulfate excess and skeletal dysplasia.

What concept does this question test?

It tests Glycosaminoglycans: mucopolysaccharidosis in Biochemistry. Corneal clouding distinguishes it from Hunter syndrome. Treatment options include haematopoietic stem cell transplantation in early disease and enzyme replacement.

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 Glycosaminoglycans: mucopolysaccharidosis?

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.