Genetic and metabolic disorders: Lesch-Nyhan syndrome: practice question

A Pediatrics 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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Pediatrics · Genetic and metabolic disorders: Lesch-Nyhan syndrome

Sample item

A 2-year-old boy has choreoathetosis, spasticity, self-mutilating biting of lips and fingers, and orange crystals in the diapers. Which enzyme is deficient?

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

The answer and the reasoning

A. Hypoxanthine-guanine phosphoribosyltransferase

Lesch-Nyhan syndrome is an X-linked disorder due to HGPRT deficiency, causing hyperuricaemia, gout, intellectual disability and compulsive self-injury. Allopurinol controls uric acid but does not prevent neurological features.

Option by option

  • A. Hypoxanthine-guanine phosphoribosyltransferase (correct)

    Correct. HGPRT deficiency defines it.

  • B. Adenosine deaminase

    ADA deficiency causes severe combined immunodeficiency.

  • C. Purine nucleoside phosphorylase

    PNP deficiency causes T-cell immunodeficiency.

  • D. Xanthine oxidase

    Xanthine oxidase deficiency causes low uric acid and xanthinuria.

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 Pediatrics question

What is the answer to this Pediatrics question?

The best answer is A, Hypoxanthine-guanine phosphoribosyltransferase. Lesch-Nyhan syndrome is an X-linked disorder due to HGPRT deficiency, causing hyperuricaemia, gout, intellectual disability and compulsive self-injury.

Why is "Adenosine deaminase" not the answer?

ADA deficiency causes severe combined immunodeficiency.

Why is "Purine nucleoside phosphorylase" not the answer?

PNP deficiency causes T-cell immunodeficiency.

Why is "Xanthine oxidase" not the answer?

Xanthine oxidase deficiency causes low uric acid and xanthinuria.

What concept does this question test?

It tests Genetic and metabolic disorders: Lesch-Nyhan syndrome in Pediatrics. Allopurinol controls uric acid but does not prevent neurological features.

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 Genetic and metabolic disorders: Lesch-Nyhan syndrome?

Memorise milestones and the vaccine schedule as tables and revise them often. Then use the flashcards and the other Pediatrics 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.