Purine metabolism: adenosine deaminase: 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 metabolism: adenosine deaminase

Sample item

Deficiency of adenosine deaminase causes severe combined immunodeficiency because accumulation of which metabolite is toxic to lymphocytes?

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

The answer and the reasoning

C. Deoxyadenosine nucleotides

ADA deficiency causes accumulation of deoxyadenosine metabolites that impair DNA synthesis and are particularly toxic to lymphocytes. This produces severe combined immunodeficiency.

Option by option

  • A. Uric acid only

    Uric acid excess is more relevant to purine overproduction disorders.

  • B. Homocysteine

    Homocysteine elevation occurs in other metabolic defects.

  • C. Deoxyadenosine nucleotides (correct)

    Correct. Toxic deoxyadenosine nucleotide accumulation damages lymphocytes.

  • D. Bilirubin

    Bilirubin is a heme-breakdown product.

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, Deoxyadenosine nucleotides. ADA deficiency causes accumulation of deoxyadenosine metabolites that impair DNA synthesis and are particularly toxic to lymphocytes.

Why is "Uric acid only" not the answer?

Uric acid excess is more relevant to purine overproduction disorders.

Why is "Homocysteine" not the answer?

Homocysteine elevation occurs in other metabolic defects.

Why is "Bilirubin" not the answer?

Bilirubin is a heme-breakdown product.

What concept does this question test?

It tests Purine metabolism: adenosine deaminase in Biochemistry. This produces severe combined immunodeficiency.

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 Purine metabolism: adenosine deaminase?

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.