Sphingolipidoses: metachromatic leukodystrophy: 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 · Sphingolipidoses: metachromatic leukodystrophy

Sample item

A 2-year-old who was previously normal develops a clumsy gait, loss of speech and a peripheral neuropathy with slowed nerve conduction. MRI shows symmetrical periventricular demyelination, and sulfatides are excreted in urine. Which enzyme is deficient?

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

The answer and the reasoning

C. Arylsulfatase A

Arylsulfatase A removes sulfate from sulfatide (galactosylceramide sulfate). Its deficiency causes sulfatide accumulation in oligodendrocytes and Schwann cells, so both central and peripheral demyelination appear; metachromatic granules are seen in nerve biopsy. Late infantile onset with motor regression and neuropathy is classic.

Option by option

  • A. Hexosaminidase A

    Hexosaminidase A deficiency is Tay-Sachs disease, with hyperacusis and a cherry-red macula.

  • B. Alpha-galactosidase A

    Alpha-galactosidase A deficiency is Fabry disease, with acral pain and angiokeratomas.

  • C. Arylsulfatase A (correct)

    Arylsulfatase A deficiency gives sulfatide storage with central and peripheral demyelination.

  • D. Galactocerebrosidase

    Galactocerebrosidase deficiency is Krabbe disease, with early irritability, globoid cells and no sulfatiduria.

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, Arylsulfatase A. Arylsulfatase A removes sulfate from sulfatide (galactosylceramide sulfate).

Why is "Hexosaminidase A" not the answer?

Hexosaminidase A deficiency is Tay-Sachs disease, with hyperacusis and a cherry-red macula.

Why is "Alpha-galactosidase A" not the answer?

Alpha-galactosidase A deficiency is Fabry disease, with acral pain and angiokeratomas.

Why is "Galactocerebrosidase" not the answer?

Galactocerebrosidase deficiency is Krabbe disease, with early irritability, globoid cells and no sulfatiduria.

What concept does this question test?

It tests Sphingolipidoses: metachromatic leukodystrophy in Biochemistry. Its deficiency causes sulfatide accumulation in oligodendrocytes and Schwann cells, so both central and peripheral demyelination appear; metachromatic granules are seen in nerve biopsy. Late infantile onset with motor regression and neuropathy is classic.

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 Sphingolipidoses: metachromatic leukodystrophy?

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.