Heterozygous Mutation of Factor V Leiden Complicating Venous Thromboembolic Syndrome: A Case Report

Factor V Leiden (FVL) is the most common hereditary thrombophilia, causing resistance to activated protein C (APC) and increasing the risk of venous thromboembolism (VTE). The coexistence of FVL and antiphospholipid syndrome (APS), an acquired autoimmune prothrombotic condition, is rare but can significantly heighten thrombotic risk. Case presentation: We report the case of a 32-year-old male presenting with an unprovoked deep vein thrombosis complicated by non-severe pulmonary embolism. The patient had no significant past medical or familial thrombotic history, but chronic smoking was noted. Laboratory evaluation revealed a heterozygous FVL mutation, resistance to APC, and a positive antiphospholipid profile. Imaging confirmed pulmonary embolism and thrombosis of the right popliteal vein. Discussion: The combination of hereditary (FVL mutation) and acquired (APS) thrombophilias creates a synergistic prothrombotic state. This rare association emphasizes the need for comprehensive thrombophilia work-up in young patients presenting with unexplained or recurrent VTE. Genetic and immunological investigations guide personalized anticoagulation strategies and familial screening. Conclusion: This case highlights the clinical relevance of identifying coexisting thrombophilic disorders. Early recognition and appropriate management are crucial to reduce recurrence and complications in patients with combined genetic and acquired risk factors for thrombosis.