Immunology: primary immunodeficiency: practice question

A Microbiology 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

Microbiology · Immunology: primary immunodeficiency

Sample item

A 4-month-old boy has persistent oral candidiasis, chronic diarrhoea and failure to thrive. Flow cytometry shows markedly reduced T cells and NK cells with normal numbers of B cells, and there is a family history of an affected maternal uncle. Which defect is most likely?

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

The answer and the reasoning

B. Mutation of the common gamma chain shared by several interleukin receptors

X-linked severe combined immunodeficiency results from mutation of the common gamma chain (IL2RG), a subunit of receptors for IL-2, IL-4, IL-7, IL-9, IL-15 and IL-21. The result is a T-negative, B-positive, NK-negative phenotype with early life-threatening infections; stem cell transplantation or gene therapy is curative. BTK, CD40L and WAS defects have different immunological profiles.

Option by option

  • A. Mutation of Bruton tyrosine kinase

    BTK deficiency causes absent B cells with normal T cell numbers.

  • B. Mutation of the common gamma chain shared by several interleukin receptors (correct)

    Correct. Loss of the common gamma chain blocks T and NK cell development.

  • C. Mutation of CD40 ligand

    CD40L deficiency gives hyper-IgM with normal T and B cell counts.

  • D. Mutation of the WAS protein

    Wiskott-Aldrich syndrome presents with eczema, thrombocytopenia and infections.

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 Microbiology questions

Questions about this Microbiology question

What is the answer to this Microbiology question?

The best answer is B, Mutation of the common gamma chain shared by several interleukin receptors. X-linked severe combined immunodeficiency results from mutation of the common gamma chain (IL2RG), a subunit of receptors for IL-2, IL-4, IL-7, IL-9, IL-15 and IL-21.

Why is "Mutation of Bruton tyrosine kinase" not the answer?

BTK deficiency causes absent B cells with normal T cell numbers.

Why is "Mutation of CD40 ligand" not the answer?

CD40L deficiency gives hyper-IgM with normal T and B cell counts.

Why is "Mutation of the WAS protein" not the answer?

Wiskott-Aldrich syndrome presents with eczema, thrombocytopenia and infections.

What concept does this question test?

It tests Immunology: primary immunodeficiency in Microbiology. The result is a T-negative, B-positive, NK-negative phenotype with early life-threatening infections; stem cell transplantation or gene therapy is curative. BTK, CD40L and WAS defects have different immunological profiles.

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 Immunology: primary immunodeficiency?

Make a one-line identity card for each organism: shape and stain, defining test, toxin, disease and drug. Then use the flashcards and the other Microbiology 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.