VKORC1 (Vitamin K Epoxide Reductase Complex Subunit 1): VKORC1 is an enzyme involved in the recycling of vitamin K, which is essential for blood clotting. Genetic variations in VKORC1 influence sensitivity to vitamin K antagonists like warfarin, affecting dosage requirements and the risk of bleeding. Testing VKORC1 can help personalize anticoagulant therapy for safer and more effective treatment.