VKORC1 rs9928829: Understanding Warfarin Sensitivity
The rs9928829 variant is a genetic polymorphism located in the promoter region of the VKORC1 gene. It is widely recognized as a primary genetic factor that influences an individual's sensitivity to the anticoagulant medication warfarin.
What each genotype means
Higher warfarin dose requirement
This genotype is associated with higher expression of the VKORC1 enzyme, which typically results in a requirement for higher doses of warfarin to achieve therapeutic anticoagulation. Individuals with this genotype are generally considered less sensitive to the drug's effects compared to those carrying the A allele. Please discuss your specific dosing requirements with your clinician or pharmacist.
This is the most common genotype in individuals of European ancestry and is also frequently observed in other populations.
Intermediate warfarin dose requirement
This genotype represents a heterozygous state that typically results in an intermediate sensitivity to warfarin compared to the GG and AA genotypes. Your body's response to the medication may require a moderate dose adjustment to reach target levels safely. Please discuss your specific dosing requirements with your clinician or pharmacist.
This genotype is commonly found across many global populations, representing a significant portion of the population in both European and Asian groups.
Increased warfarin sensitivity
This genotype is associated with lower expression of the VKORC1 enzyme, which makes individuals significantly more sensitive to the effects of warfarin. Carrying this genotype is linked to a higher risk of over-coagulation and bleeding if standard doses are used, often necessitating lower starting doses. Please discuss your specific dosing requirements with your clinician or pharmacist.
This genotype is highly prevalent in East Asian populations and is also found in a smaller percentage of individuals of European ancestry.
What is the rs9928829 Variant?
The rs9928829 variant is a single nucleotide polymorphism (SNP) situated within the promoter region of the VKORC1 gene. In scientific literature, this specific variant is frequently referred to as -1639 G>A. Because it is located in the promoter region—the "on-off switch" area of a gene—it can influence how much of the VKORC1 protein is produced by the body. Variations in this region are significant because they can alter the expression levels of the target enzyme, which in turn affects how the body processes certain medications. Researchers study this SNP because it serves as a key marker for predicting how patients might respond to specific therapeutic interventions, particularly those involving blood-thinning agents.
The Role of the VKORC1 Gene
The VKORC1 gene provides instructions for making the vitamin K epoxide reductase complex subunit 1 enzyme. This enzyme is essential for the body's ability to recycle vitamin K, which is a critical component in the production of proteins that help blood clot. Warfarin works by inhibiting this enzyme, effectively reducing the amount of active vitamin K available and thereby slowing the blood clotting process. Because VKORC1 is the direct pharmacological target of warfarin, any genetic variation that changes the amount or activity of this enzyme can significantly impact how much medication a patient needs to achieve a therapeutic effect. Understanding this gene is a cornerstone of modern pharmacogenomics.
Research and Clinical Associations
Extensive research has established that the rs9928829 variant is strongly associated with warfarin dosage requirements. Individuals who carry the A allele are generally found to be more sensitive to warfarin, often requiring lower doses to reach the desired therapeutic range compared to those who carry the G allele. This association is considered a major genetic determinant of warfarin response, often studied alongside variants in the CYP2C9 gene. While the evidence linking this variant to dosing requirements is robust, it is important to note that clinical dosing decisions are complex. Clinicians use algorithms that incorporate genetic data, patient demographics, and clinical factors to determine appropriate therapy. This information should never be used to self-adjust medication; always consult with a healthcare provider or pharmacist regarding your specific treatment plan.
Population Frequency
The distribution of the rs9928829 variant varies significantly across different global populations. Research indicates that the variant is common in both European and Asian populations, though the specific frequency of the A and G alleles can differ between these groups. Because allele frequencies are not uniform worldwide, the prevalence of warfarin sensitivity linked to this SNP also shows geographic and ancestral variation. Understanding these population-specific differences is an active area of study in pharmacogenomics, as it helps refine dosing guidelines to be more inclusive and accurate for diverse patient groups. Genetic testing data should always be interpreted within the context of an individual's broader clinical profile.
How common is this variant?
The rs9928829 variant is common in European and Asian populations, with allele frequencies varying significantly between different ancestral groups.
Frequently asked questions
Does having the A allele mean I cannot take warfarin?
No, having the A allele does not mean you cannot take warfarin. It simply means your body may be more sensitive to the drug, and your doctor will use this information to calculate a safer, more effective starting dose for you.
Should I get tested for VKORC1 before starting warfarin?
Pharmacogenomic testing is sometimes used to help guide initial dosing, but it is not always required for every patient. You should discuss with your doctor whether genetic testing is appropriate for your specific medical situation.
Can I use this information to change my own dose?
Absolutely not. You must never change your medication dosage based on genetic information without consulting your healthcare provider. Adjusting warfarin doses incorrectly can lead to serious health risks, including bleeding or clotting.
Is VKORC1 the only gene that affects warfarin?
No, other genes, such as CYP2C9, also play a significant role in how the body metabolizes warfarin. Doctors often consider multiple genetic and clinical factors when determining the best treatment plan.
Sources & further reading
Educational information only, last refreshed 9/23/2026. Not medical advice — these associations describe population statistics, not individual predictions.
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Intronic regulatory variant in VKORC1 associated with warfarin maintenance dose requirements and anticoagulant sensitivity.
Located in VKORC1, this missense variant (p.Val66Met) causes severe clinical warfarin resistance requiring significantly elevated therapeutic dosages.
Intronic regulatory variant in VKORC1 in high linkage disequilibrium with rs9923231, dictating clinical warfarin dosing requirements.
The A allele at VKORC1 -1639G>A confers increased sensitivity to warfarin, typically requiring lower maintenance doses to prevent bleeding complications.
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 variant is a well-established marker in the VKORC1 gene often used in studies regarding warfarin sensitivity and dosing.