Blood and immunity: lysosomal trafficking defect in phagocytes: 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.

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Physiology · Blood and immunity: lysosomal trafficking defect in phagocytes

Sample item

A child with partial albinism and silvery hair has recurrent pyogenic infections, and blood films show giant cytoplasmic granules in neutrophils. Which defect underlies the infections?

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

The answer and the reasoning

C. Defective lysosomal trafficking, impairing phagosome-lysosome fusion

In Chediak-Higashi syndrome a mutation in the lysosomal trafficking regulator gene LYST causes giant lysosomal granules and poor phagosome-lysosome fusion, so bacterial killing is impaired. Melanosome defects explain the albinism, and neuropathy and cytopenias may follow.

Option by option

  • A. Defective integrin CD18, preventing neutrophil adhesion

    CD18 defects cause leucocyte adhesion deficiency with delayed cord separation and no pus.

  • B. Absent NADPH oxidase, with no respiratory burst

    Absent NADPH oxidase gives chronic granulomatous disease, with normal granules.

  • C. Defective lysosomal trafficking, impairing phagosome-lysosome fusion (correct)

    Correct. Faulty lysosomal trafficking fits the giant granules and the albinism.

  • D. Absent Btk, with no mature B cells

    Absent Btk causes agammaglobulinaemia without giant granules or albinism.

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 Physiology question

What is the answer to this Physiology question?

The best answer is C, Defective lysosomal trafficking, impairing phagosome-lysosome fusion. In Chediak-Higashi syndrome a mutation in the lysosomal trafficking regulator gene LYST causes giant lysosomal granules and poor phagosome-lysosome fusion, so bacterial killing is impaired.

Why is "Defective integrin CD18, preventing neutrophil adhesion" not the answer?

CD18 defects cause leucocyte adhesion deficiency with delayed cord separation and no pus.

Why is "Absent NADPH oxidase, with no respiratory burst" not the answer?

Absent NADPH oxidase gives chronic granulomatous disease, with normal granules.

Why is "Absent Btk, with no mature B cells" not the answer?

Absent Btk causes agammaglobulinaemia without giant granules or albinism.

What concept does this question test?

It tests Blood and immunity: lysosomal trafficking defect in phagocytes in Physiology. Melanosome defects explain the albinism, and neuropathy and cytopenias may follow.

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: lysosomal trafficking defect in phagocytes?

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.