Immunodeficiency: severe combined immunodeficiency: practice question

A Pathology 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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Pathology · Immunodeficiency: severe combined immunodeficiency

Sample item

A 4-month-old boy has persistent oral candidiasis, chronic diarrhoea, failure to thrive and Pneumocystis pneumonia. Lymphocyte count is low and no thymic shadow is seen. Which statement about the commonest form and its definitive treatment is correct?

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

The answer and the reasoning

C. It is usually X-linked from a common gamma chain mutation and is cured by haematopoietic stem cell transplantation

SCID presents in the first months with opportunistic infections, diarrhoea and failure to thrive. The commonest form is X-linked, caused by mutation of the common gamma chain of cytokine receptors (IL2RG), which impairs T and NK cell development. It is a paediatric emergency, live vaccines such as BCG are contraindicated, and definitive treatment is haematopoietic stem cell transplantation.

Option by option

  • A. It is usually from a BTK mutation and is managed by lifelong immunoglobulin

    BTK mutation causes agammaglobulinaemia, in which T cells are normal and thymic shadow is present.

  • B. It is usually from CD40 ligand deficiency and is managed by prophylactic antibiotics alone

    CD40 ligand deficiency causes hyper-IgM syndrome with intact T-cell numbers.

  • C. It is usually X-linked from a common gamma chain mutation and is cured by haematopoietic stem cell transplantation (correct)

    Correct. IL2RG mutation is the commonest cause and transplantation is curative.

  • D. It is usually autosomal from ADA deficiency and is managed by IVIG alone

    ADA deficiency is the second commonest form, and IVIG alone does not restore T-cell function.

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 Pathology question

What is the answer to this Pathology question?

The best answer is C, It is usually X-linked from a common gamma chain mutation and is cured by haematopoietic stem cell transplantation. SCID presents in the first months with opportunistic infections, diarrhoea and failure to thrive.

Why is "It is usually from a BTK mutation and is managed by lifelong immunogl…" not the answer?

BTK mutation causes agammaglobulinaemia, in which T cells are normal and thymic shadow is present.

Why is "It is usually from CD40 ligand deficiency and is managed by prophylac…" not the answer?

CD40 ligand deficiency causes hyper-IgM syndrome with intact T-cell numbers.

Why is "It is usually autosomal from ADA deficiency and is managed by IVIG al…" not the answer?

ADA deficiency is the second commonest form, and IVIG alone does not restore T-cell function.

What concept does this question test?

It tests Immunodeficiency: severe combined immunodeficiency in Pathology. The commonest form is X-linked, caused by mutation of the common gamma chain of cytokine receptors (IL2RG), which impairs T and NK cell development. It is a paediatric emergency, live vaccines such as BCG are contraindicated, and definitive treatment is haematopoietic stem cell transplantation.

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 Immunodeficiency: severe combined immunodeficiency?

Learn each disease as a bundle: cause, key histology, markers, and the clinical hallmark. Then use the flashcards and the other Pathology 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.