VKORC1 rs3745274: Understanding Warfarin Resistance
The rs3745274 variant is a rare genetic change located within the VKORC1 gene. It is associated with clinical warfarin resistance, a condition where individuals require higher-than-average doses of the anticoagulant medication to achieve a therapeutic effect.
What each genotype means
Typical warfarin response
This genotype represents the common, wild-type sequence for this position in the VKORC1 gene. Individuals with this profile do not carry the specific missense variant associated with severe warfarin resistance. Please discuss your medication management and any necessary dosing adjustments with your clinician or pharmacist.
This is the most common genotype observed in the general population.
Potential warfarin resistance
This genotype indicates you carry one copy of the variant associated with warfarin resistance. Research suggests that individuals with this variant may require higher therapeutic dosages of warfarin to achieve the desired clinical effect. Please consult your healthcare provider or pharmacist to discuss how this genetic information may influence your treatment plan.
This genotype is rare globally, typically observed only in specific cohorts identified with warfarin resistance.
Increased warfarin resistance
This genotype indicates you carry two copies of the variant associated with warfarin resistance. Clinical evidence suggests that individuals with this profile may exhibit significantly reduced sensitivity to warfarin, often requiring elevated dosages to reach therapeutic targets. It is essential to discuss this finding with your clinician or pharmacist to ensure your medication regimen is appropriately managed.
This genotype is extremely rare in the general population and is primarily documented in clinical studies of patients with documented warfarin resistance.
What is the rs3745274 Variant?
The rs3745274 variant is a specific single nucleotide polymorphism (SNP) found within the VKORC1 gene, which is located on chromosome 16. In the context of genetics, a SNP represents a variation at a single position in the DNA sequence. This particular variant is classified as a missense mutation, meaning it results in a change to the amino acid sequence of the protein produced by the gene. Specifically, this variant is known as p.Val66Met. Because the VKORC1 gene provides instructions for making an enzyme that is essential for the blood-clotting process, changes to its structure can alter how the body responds to medications that target this pathway. While many variants in the human genome are common, rs3745274 is considered rare, appearing primarily in specific clinical cohorts rather than the general population.
The Role of the VKORC1 Gene
The VKORC1 gene encodes the vitamin K epoxide reductase complex subunit 1 enzyme. This enzyme plays a critical role in the vitamin K cycle, which is necessary for the activation of several clotting factors in the blood. Warfarin, a commonly prescribed anticoagulant, works by inhibiting this enzyme, thereby reducing the body's ability to form blood clots. Because VKORC1 is the direct pharmacological target of warfarin, the amount of functional enzyme present in a person's system significantly influences how much medication is needed to achieve the desired level of anticoagulation. When a genetic variant like rs3745274 alters the structure or function of this enzyme, it can change the binding affinity of the drug or the overall efficiency of the enzyme, leading to variations in how patients respond to standard dosing protocols.
Clinical Associations and Evidence
Research has associated the rs3745274 variant with clinical warfarin resistance. Patients carrying this variant often require significantly elevated therapeutic dosages of warfarin to maintain a safe and effective level of anticoagulation compared to individuals without the variant. The evidence for this association is categorized as limited, as it is primarily derived from studies of specific patient cohorts who were already identified as having unusual responses to anticoagulant therapy. While the functional impact of such missense mutations on the VKORC1 enzyme has been demonstrated in laboratory assays, clinical data is less extensive than for more common regulatory variants in the same gene. It is important to note that warfarin response is a complex trait influenced by multiple genetic factors, including other variants in VKORC1 and the CYP2C9 gene, as well as environmental factors like diet and concurrent medications.
Navigating Your Genetic Information
If you have received information regarding your status for the rs3745274 variant, it is essential to understand that this is only one piece of a much larger clinical puzzle. Genetic testing for pharmacogenomics is intended to provide clinicians with additional data to help optimize medication management, but it should never be used to make independent medical decisions. If you are currently taking warfarin or are expected to begin anticoagulant therapy, you must discuss your genetic results with your healthcare provider or a clinical pharmacist. They are trained to interpret these findings in the context of your overall health, medical history, and other medications. Never adjust your medication dosage based on genetic reports without direct supervision from your medical team, as improper dosing can lead to serious health risks, including an increased chance of blood clots or bleeding complications.
How common is this variant?
The rs3745274 variant is rare globally, with a frequency of less than 0.005. It is observed primarily in clinical cohorts of patients who have demonstrated resistance to warfarin therapy.
Frequently asked questions
What does it mean to be warfarin resistant?
Warfarin resistance means that a person requires a higher-than-average dose of the medication to achieve the desired blood-thinning effect. This can be caused by genetic factors, such as variants in the VKORC1 gene, or by environmental factors.
Should I get tested for VKORC1 variants?
Pharmacogenetic testing is typically ordered by a physician when a patient is starting or struggling with anticoagulant therapy. You should discuss the necessity and potential benefits of such testing with your doctor.
Can I change my genotype?
No, your genotype is determined by the DNA you inherited from your parents and cannot be changed. However, understanding your genotype can help your healthcare provider tailor your medical treatment.
Is rs3745274 the only variant that affects warfarin?
No, warfarin response is influenced by many genetic variants, including others in the VKORC1 gene and the CYP2C9 gene. Clinical dosing models often consider multiple genetic and non-genetic factors simultaneously.
Sources & further reading
Educational information only, last refreshed 9/21/2026. Not medical advice — these associations describe population statistics, not individual predictions.
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The VKORC1 -1639G>A promoter variant reduces vitamin K epoxide reductase subunit 1 expression, requiring lower therapeutic warfarin maintenance doses to prevent bleeding complications.
This VKORC1 variant is a clinically useful marker for sensitivity to warfarin and related vitamin-K-antagonist dosing, with direct implications for medication safety.
Promoter variant in VKORC1 influencing warfarin sensitivity and dosing requirements.
Regulatory variant in the VKORC1 promoter region that significantly influences warfarin dose requirements.
Intronic regulatory variant in VKORC1 in high linkage disequilibrium with rs9923231, dictating clinical warfarin dosing requirements.
This variant is a well-established marker in the VKORC1 gene often used in studies regarding warfarin sensitivity and dosing.