Purine salvage: hypoxanthine-guanine phosphoribosyltransferase: 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 · Purine salvage: hypoxanthine-guanine phosphoribosyltransferase

Sample item

A 22-year-old man with normal intelligence develops early gout and uric acid stones. Enzyme assay shows a small residual activity of the same salvage enzyme that is absent in Lesch-Nyhan syndrome. Which enzyme is it?

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

The answer and the reasoning

B. Hypoxanthine-guanine phosphoribosyltransferase

Partial deficiency of the salvage enzyme gives the Kelley-Seegmiller variant, with gout and stones but without the neurological and behavioural features of the complete defect. The residual activity protects the brain. Complete deficiency produces Lesch-Nyhan syndrome.

Option by option

  • A. Purine nucleoside phosphorylase

    Purine nucleoside phosphorylase deficiency causes T-cell immunodeficiency with low urate.

  • B. Hypoxanthine-guanine phosphoribosyltransferase (correct)

    Correct. Partial loss of this enzyme causes the Kelley-Seegmiller variant with gout but normal neurology.

  • C. Adenine phosphoribosyltransferase

    Adenine phosphoribosyltransferase deficiency presents with 2,8-dihydroxyadenine stones, not gout.

  • D. Phosphoribosyl pyrophosphate synthetase

    PRPP synthetase superactivity raises PRPP and may cause gout with deafness.

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, Hypoxanthine-guanine phosphoribosyltransferase. Partial deficiency of the salvage enzyme gives the Kelley-Seegmiller variant, with gout and stones but without the neurological and behavioural features of the complete defect.

Why is "Purine nucleoside phosphorylase" not the answer?

Purine nucleoside phosphorylase deficiency causes T-cell immunodeficiency with low urate.

Why is "Adenine phosphoribosyltransferase" not the answer?

Adenine phosphoribosyltransferase deficiency presents with 2,8-dihydroxyadenine stones, not gout.

Why is "Phosphoribosyl pyrophosphate synthetase" not the answer?

PRPP synthetase superactivity raises PRPP and may cause gout with deafness.

What concept does this question test?

It tests Purine salvage: hypoxanthine-guanine phosphoribosyltransferase in Biochemistry. The residual activity protects the brain. Complete deficiency produces Lesch-Nyhan syndrome.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. 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 Purine salvage: hypoxanthine-guanine phosphoribosyltransferase?

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.