Immunology: 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.

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Microbiology · Immunology

Sample item

A boy aged 18 months has recurrent otitis, sinusitis and pneumonia due to encapsulated bacteria. All immunoglobulin classes are very low and CD19-positive B cells are absent, with normal T cells. What is the diagnosis?

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

The answer and the reasoning

A. X-linked agammaglobulinaemia

Bruton agammaglobulinaemia is due to a BTK gene mutation that blocks B cell maturation. Infections begin after maternal IgG wanes at about six months and mainly involve encapsulated bacteria, with low immunoglobulins and absent B cells.

Option by option

  • A. X-linked agammaglobulinaemia (correct)

    A BTK defect produces absent B cells and low immunoglobulins with normal T cells.

  • B. DiGeorge syndrome

    DiGeorge syndrome involves thymic hypoplasia with T cell deficiency and hypocalcaemia.

  • C. Severe combined immunodeficiency

    SCID has defective T cells and presents earlier with severe viral and fungal infections.

  • D. Chronic granulomatous disease

    Chronic granulomatous disease is a phagocyte defect with infections by catalase-positive organisms.

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 A, X-linked agammaglobulinaemia. Bruton agammaglobulinaemia is due to a BTK gene mutation that blocks B cell maturation.

Why is "DiGeorge syndrome" not the answer?

DiGeorge syndrome involves thymic hypoplasia with T cell deficiency and hypocalcaemia.

Why is "Severe combined immunodeficiency" not the answer?

SCID has defective T cells and presents earlier with severe viral and fungal infections.

Why is "Chronic granulomatous disease" not the answer?

Chronic granulomatous disease is a phagocyte defect with infections by catalase-positive organisms.

What concept does this question test?

It tests Immunology in Microbiology. Infections begin after maternal IgG wanes at about six months and mainly involve encapsulated bacteria, with low immunoglobulins and absent B 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 Immunology?

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.