Activated protein C resistance is the most common inherited thrombophilia in Caucasian populations. The molecular basis is:
- A A point mutation in the F5 gene replacing arginine 506 with glutamine at the APC cleavage site of factor V ✓
- B A deletion in the PROC gene abolishing protein C synthesis
- C An autoantibody that binds and neutralizes activated protein C
- D Overexpression of tissue factor pathway inhibitor
Correct answer: A. A point mutation in the F5 gene replacing arginine 506 with glutamine at the APC cleavage site of factor V
Explanation
Factor V Leiden is a G to A point mutation in the F5 gene that substitutes glutamine for arginine at position 506, the site cleaved by activated protein C. Mutant factor Va resists inactivation, persists longer, and sustains thrombin generation, producing venous thrombosis risk especially in homozygotes and in combination with estrogen therapy. It does not affect arterial thrombosis risk substantially. Protein C gene defects are a separate, less common disorder.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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