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VKORC1 gene
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Gene

VKORC1 gene

The VKORC1 gene provides instructions for an enzyme that activates clotting proteins, playing a critical role in how the body responds to the anticoagulant medication warfarin.

Overview

The VKORC1 gene provides instructions for making a vitamin K epoxide reductase enzyme. Primarily produced in the liver, this enzyme spans the membrane of the endoplasmic reticulum, a structure involved in protein processing and transport. The VKORC1 enzyme converts one form of vitamin K into another, which is necessary to activate clotting proteins in the pathway that forms blood clots.

Health Conditions Related to Genetic Changes

Warfarin resistance

Variations (polymorphisms) in the VKORC1 gene are associated with warfarin resistance, where individuals require higher doses of the anticoagulant warfarin. Warfarin works by binding to the VKORC1 enzyme and inhibiting the activation of clotting proteins.

  • The most common polymorphism involves replacing the amino acid aspartic acid with tyrosine at position 36 (Asp36Tyr or D36Y).
  • This change reduces the enzyme's ability to bind to warfarin, necessitating higher doses to achieve the desired anticoagulant effect.

Warfarin sensitivity

Other polymorphisms are associated with warfarin sensitivity, where individuals require lower doses of the drug.

  • The most common polymorphism, known as VKORC1A, involves a change in a DNA building block near the gene (-1639G>A).
  • This change reduces the amount of VKORC1 enzyme available, meaning lower doses of warfarin are required to inhibit the enzyme.
  • Taking standard doses can lead to an overdose, causing abnormal bleeding in the brain, gastrointestinal tract, or other tissues.

Other Names for This Gene

  • FLJ00289
  • vitamin K 1 2,3-epoxide reductase subunit 1
  • vitamin K epoxide reductase complex, subunit 1
  • VKOR

Frequently Asked Questions

Because a sensitive VKORC1 genotype can cause the standard dose to overshoot the therapeutic range, watch for unexpected bruising, nosebleeds, bleeding gums, blood in urine or stool, dark‑colored tarry stools, or sudden severe headache (possible intracranial bleed). If any of these occur, check your INR immediately (target usually 2‑3 for most indications) and contact your healthcare team; prompt dose reduction or vitamin K reversal may be needed.
If you carry the common -1639G>A (VKORC1A) variant, your liver makes less VKORC1 enzyme, so you usually require a lower warfarin dose (often 30‑50 % less than standard). Conversely, the Asp36Tyr (D36Y) variant makes the enzyme less sensitive to warfarin, meaning you may need a higher dose to reach therapeutic INR. Your prescribing clinician will use the genotype, together with age, weight, diet, and other meds, to calculate an individualized starting dose and then adjust based on INR monitoring.
Testing is recommended when warfarin is being considered for the first time, especially in patients at high risk of bleeding (elderly, liver disease, interacting drugs) or when rapid anticoagulation is needed. A simple blood test can identify the -1639G>A and D36Y polymorphisms; the results are returned in a few days and can prevent over‑ or under‑dosing right from the start. Discuss testing with your provider; many anticoagulation clinics include it as part of their protocol.
Patients with D36Y often need warfarin doses >10 mg/day, which can be difficult to manage. Direct oral anticoagulators (DOACs) such as apixaban, rivaroxaban, dabigatran, or edoxaban do not rely on VKORC1 for their effect and are usually effective regardless of VKORC1 genotype. Discuss with your cardiologist or hematologist; DOACs have different dosing, renal clearance requirements, and may not be suitable for mechanical heart valves or certain clotting disorders, but they are a common alternative for warfarin‑resistant individuals.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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