A 22-year-old man presents with recurrent deep vein thrombosis. Testing reveals resistance to activated protein C on the coagulation assay. No mutation is found in the protein C gene. What is the most likely underlying genetic defect?
- A Prothrombin G20210A mutation
- B Factor V Leiden mutation ✓
- C Protein S deficiency
- D Antithrombin III deficiency
Correct answer: B. Factor V Leiden mutation
Explanation
Factor V Leiden is a point mutation (Arg506Gln) that renders factor Va resistant to cleavage by activated protein C, causing the most common inherited thrombophilia. The activated protein C resistance assay is the screening test. Prothrombin mutation elevates prothrombin levels but does not cause APC resistance. Protein S and AT III deficiencies are detected by antigen/activity assays, not APC resistance testing.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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