Blood and immunity: adenosine deaminase deficiency: practice question

A Physiology 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.

Try it

Physiology · Blood and immunity: adenosine deaminase deficiency

Sample item

An infant has persistent infections with almost no T or B lymphocytes. Lymphocytes accumulate deoxyadenosine triphosphate, which inhibits ribonucleotide reductase. Which enzyme is deficient?

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

The answer and the reasoning

B. Adenosine deaminase

Adenosine deaminase deficiency allows deoxyadenosine and dATP to build up, which inhibits ribonucleotide reductase and kills dividing T and B lymphocytes, producing severe combined immunodeficiency. Purine nucleoside phosphorylase deficiency instead accumulates dGTP and mainly affects T cells.

Option by option

  • A. Xanthine oxidase

    Xanthine oxidase deficiency causes xanthinuria and low uric acid.

  • B. Adenosine deaminase (correct)

    Correct. ADA deficiency causes dATP accumulation and combined T and B lymphocyte loss.

  • C. Hypoxanthine-guanine phosphoribosyltransferase

    HGPRT deficiency causes Lesch-Nyhan syndrome with hyperuricaemia, not immunodeficiency.

  • D. Purine nucleoside phosphorylase

    PNP deficiency accumulates dGTP and mainly damages T cells.

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.

More Physiology questions

Questions about this Physiology question

What is the answer to this Physiology question?

The best answer is B, Adenosine deaminase. Adenosine deaminase deficiency allows deoxyadenosine and dATP to build up, which inhibits ribonucleotide reductase and kills dividing T and B lymphocytes, producing severe combined immunodeficiency.

Why is "Xanthine oxidase" not the answer?

Xanthine oxidase deficiency causes xanthinuria and low uric acid.

Why is "Hypoxanthine-guanine phosphoribosyltransferase" not the answer?

HGPRT deficiency causes Lesch-Nyhan syndrome with hyperuricaemia, not immunodeficiency.

Why is "Purine nucleoside phosphorylase" not the answer?

PNP deficiency accumulates dGTP and mainly damages T cells.

What concept does this question test?

It tests Blood and immunity: adenosine deaminase deficiency in Physiology. Purine nucleoside phosphorylase deficiency instead accumulates dGTP and mainly affects T cells.

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 Blood and immunity: adenosine deaminase deficiency?

For each system, sketch the key graph (pressure–volume loop, oxygen dissociation curve, nephron handling) and explain it aloud. Then use the flashcards and the other Physiology 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.