A 40-year-old man presents with recurrent deep vein thrombosis (DVT) and cerebral venous sinus thrombosis (CVST). He has a family history of similar events. Blood tests show: PT: Normal APTT: Normal Protein C & S: Normal Factor V Leiden mutation: Positive What is the most likely diagnosis? A) Antiphospholipid syndrome B) Protein C deficiency C) Factor V Leiden mutation D) Prothrombin gene mutation E) Heparin-induced thrombocytopenia Correct Answer: C) Factor V Leiden mutation Explanation: Factor V Leiden is the most common inherited thrombophilia, causing: Recurrent venous thrombosis (DVT, CVST, PE) Resistant to inactivation by Protein C A) Antiphospholipid syndrome → Incorrect. Causes arterial & venous thrombosis + prolonged APTT. B) Protein C deficiency → Incorrect. Causes thrombosis but has low protein C levels. D) Prothrombin gene mutation → Incorrect. Less common cause of hypercoagulability. E) Heparin-induced thrombocytopenia → Incorrect. Causes thrombosis + low platelets after heparin use. Key Tips for PLAB 1: ✅ Recurrent DVT/PE in young patient = Suspect Factor V Leiden. ✅ Diagnosis: Genetic testing for mutation. ✅ Treatment: Long-term anticoagulation if recurrent thrombosis.
