Nucleotide metabolism: Lesch-Nyhan 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 · Nucleotide metabolism: Lesch-Nyhan syndrome

Sample item

A boy has self-injurious behavior, dystonia, hyperuricemia, and orange urate crystals in diapers. Which enzyme deficiency is most likely?

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

The answer and the reasoning

B. HGPRT deficiency

Lesch-Nyhan syndrome results from hypoxanthine-guanine phosphoribosyltransferase deficiency, impairing purine salvage and increasing uric acid production. Neurologic dysfunction and self-injury are characteristic.

Option by option

  • A. Thymidylate synthase deficiency

    Thymidylate synthase deficiency is not this syndrome.

  • B. HGPRT deficiency (correct)

    Correct. HGPRT deficiency causes the classic neurologic and urate phenotype.

  • C. Adenosine deaminase deficiency

    ADA deficiency causes immunodeficiency.

  • D. Xanthine oxidase deficiency

    Xanthine oxidase deficiency lowers uric acid rather than causing hyperuricemia.

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 B, HGPRT deficiency. Lesch-Nyhan syndrome results from hypoxanthine-guanine phosphoribosyltransferase deficiency, impairing purine salvage and increasing uric acid production.

Why is "Thymidylate synthase deficiency" not the answer?

Thymidylate synthase deficiency is not this syndrome.

Why is "Adenosine deaminase deficiency" not the answer?

ADA deficiency causes immunodeficiency.

Why is "Xanthine oxidase deficiency" not the answer?

Xanthine oxidase deficiency lowers uric acid rather than causing hyperuricemia.

What concept does this question test?

It tests Nucleotide metabolism: Lesch-Nyhan syndrome in Biochemistry. Neurologic dysfunction and self-injury are characteristic.

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 Nucleotide metabolism: Lesch-Nyhan 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.