Haematology: factor V Leiden: 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 · Haematology: factor V Leiden

Sample item

A 24-year-old woman taking an oral contraceptive pill develops left leg deep vein thrombosis. Her mother also had venous thrombosis at a young age. Which defect is the most common inherited cause of her predisposition?

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

The answer and the reasoning

D. Factor V resistant to inactivation by activated protein C

Factor V Leiden is a point mutation (Arg506Gln) that makes factor V resistant to cleavage by activated protein C, so procoagulant activity persists. It is the commonest inherited thrombophilia, with a particular frequency in people of European descent, and risk increases with oestrogen use. The activated protein C resistance assay and genetic testing confirm it.

Option by option

  • A. Deficiency of protein S

    Protein S deficiency is a rare cause of venous thrombosis.

  • B. Increased prothrombin levels due to a promoter mutation

    Increased prothrombin from the G20210A variant is the second commonest, but it is less frequent than factor V Leiden.

  • C. Deficiency of antithrombin

    Antithrombin deficiency is a rarer thrombophilia, and causes heparin resistance.

  • D. Factor V resistant to inactivation by activated protein C (correct)

    Correct. The mutant factor V cannot be degraded by activated protein C, which promotes thrombosis.

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 D, Factor V resistant to inactivation by activated protein C. Factor V Leiden is a point mutation (Arg506Gln) that makes factor V resistant to cleavage by activated protein C, so procoagulant activity persists.

Why is "Deficiency of protein S" not the answer?

Protein S deficiency is a rare cause of venous thrombosis.

Why is "Increased prothrombin levels due to a promoter mutation" not the answer?

Increased prothrombin from the G20210A variant is the second commonest, but it is less frequent than factor V Leiden.

Why is "Deficiency of antithrombin" not the answer?

Antithrombin deficiency is a rarer thrombophilia, and causes heparin resistance.

What concept does this question test?

It tests Haematology: factor V Leiden in Pathology. It is the commonest inherited thrombophilia, with a particular frequency in people of European descent, and risk increases with oestrogen use. The activated protein C resistance assay and genetic testing confirm it.

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 Haematology: factor V Leiden?

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.