Biomolecules and enzymes: integrin defect in Glanzmann thrombasthenia: 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 · Biomolecules and enzymes: integrin defect in Glanzmann thrombasthenia

Sample item

A child has recurrent mucocutaneous bleeding with a normal platelet count and normal PT and aPTT. Platelets fail to aggregate with ADP, collagen and epinephrine, but aggregate with ristocetin. Which protein is defective?

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

The answer and the reasoning

C. Integrin alpha-IIb beta-3 (glycoprotein IIb/IIIa)

In Glanzmann thrombasthenia the integrin alpha-IIb beta-3 receptor is deficient, so platelets cannot bind fibrinogen and cannot form aggregates. Ristocetin-induced agglutination depends on GPIb and von Willebrand factor, which are intact. Integrins are transmembrane receptors that link the extracellular matrix to the cytoskeleton.

Option by option

  • A. Von Willebrand factor multimers

    Von Willebrand factor deficiency would abolish ristocetin aggregation, which is normal here.

  • B. Glycoprotein Ib-IX-V complex

    A defective GPIb-IX-V complex (Bernard-Soulier syndrome) abolishes ristocetin response and gives giant platelets.

  • C. Integrin alpha-IIb beta-3 (glycoprotein IIb/IIIa) (correct)

    Correct. Absence of the fibrinogen receptor integrin alpha-IIb beta-3 prevents aggregation with all physiological agonists.

  • D. Plasma fibrinogen

    Plasma fibrinogen is normal in Glanzmann disease; the receptor that binds it is missing.

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, Integrin alpha-IIb beta-3 (glycoprotein IIb/IIIa). In Glanzmann thrombasthenia the integrin alpha-IIb beta-3 receptor is deficient, so platelets cannot bind fibrinogen and cannot form aggregates.

Why is "Von Willebrand factor multimers" not the answer?

Von Willebrand factor deficiency would abolish ristocetin aggregation, which is normal here.

Why is "Glycoprotein Ib-IX-V complex" not the answer?

A defective GPIb-IX-V complex (Bernard-Soulier syndrome) abolishes ristocetin response and gives giant platelets.

Why is "Plasma fibrinogen" not the answer?

Plasma fibrinogen is normal in Glanzmann disease; the receptor that binds it is missing.

What concept does this question test?

It tests Biomolecules and enzymes: integrin defect in Glanzmann thrombasthenia in Biochemistry. Ristocetin-induced agglutination depends on GPIb and von Willebrand factor, which are intact. Integrins are transmembrane receptors that link the extracellular matrix to the cytoskeleton.

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 Biomolecules and enzymes: integrin defect in Glanzmann thrombasthenia?

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.