CYP2C9 rs1057911: What Your Genotype Means
The rs1057911 variant is a specific genetic change in the CYP2C9 gene that defines the *3 allele. This variant is associated with significantly reduced enzymatic activity, which can influence how the body processes certain medications like warfarin.
What each genotype means
Normal enzyme activity
This genotype represents the most common form of the CYP2C9 gene, often referred to as the wild-type or *1 allele. Individuals with this profile typically exhibit standard metabolic activity for medications processed by this enzyme. Please discuss any medication dosing or concerns with your clinician or pharmacist.
This is the most common genotype found across all global populations.
Reduced enzyme activity
This genotype indicates you carry one copy of the T allele, which is associated with the CYP2C9*3 variant. Research suggests this variant may lead to decreased enzymatic activity, which can influence how your body processes certain drugs like warfarin. You should consult with your healthcare provider or pharmacist regarding any potential impact on medication dosing.
Carried by a small percentage of the population, with frequencies varying significantly by ancestry, typically ranging from 1% to 8%.
Significantly reduced enzyme activity
This genotype indicates you carry two copies of the T allele. This profile is associated with a more pronounced reduction in CYP2C9 enzymatic function compared to those with one or no copies of the variant. Because this can affect the metabolism of specific medications, it is important to discuss your genetic profile with your clinician or pharmacist before starting or adjusting any relevant treatments.
This is a rare genotype observed in a very small fraction of the population across most ancestries.
Understanding the rs1057911 Variant
The rs1057911 variant is a single nucleotide polymorphism (SNP) located within the CYP2C9 gene. In the scientific literature, this specific genetic change is responsible for the amino acid substitution known as p.Ile359Leu, which is the defining feature of the CYP2C9*3 allele. Because this change occurs in a critical region of the enzyme, it significantly impairs the protein's ability to function normally. While the human genome contains many variations, rs1057911 is particularly notable in the field of pharmacogenomics due to its well-documented impact on drug metabolism. When an individual carries this variant, the resulting enzyme is less efficient at breaking down specific substrates, which can lead to higher concentrations of those drugs in the bloodstream compared to individuals with the more common, fully functional version of the gene.
The Role of the CYP2C9 Gene
The CYP2C9 gene provides instructions for making an enzyme that belongs to the cytochrome P450 family. These enzymes are primarily responsible for detoxifying or metabolizing a wide range of substances, including many prescription medications. CYP2C9 is specifically involved in the metabolism of several drugs, most notably the anticoagulant warfarin, which is used to prevent blood clots. By breaking down these drugs, the enzyme helps the body clear them from the system at a predictable rate. When the gene carries a variant like rs1057911, the resulting enzyme may have reduced or nearly absent activity. For drugs with a narrow therapeutic index—meaning the difference between a safe dose and a toxic dose is small—this reduction in metabolic capacity can be clinically significant, as it may cause the drug to remain active in the body for a longer period than intended.
Clinical Associations and Evidence
Research has consistently associated the rs1057911 variant with altered responses to medications such as warfarin and phenytoin. Studies indicate that individuals carrying the *3 allele (defined by rs1057911) often require lower maintenance doses of warfarin to achieve a therapeutic effect. Because these individuals metabolize the drug more slowly, they may be at an increased risk of over-anticoagulation and bleeding events if standard, higher doses are administered. While the evidence linking this variant to warfarin dosing is strong and supported by clinical guidelines from organizations like CPIC and the FDA, it is important to note that genetics is only one factor in drug response. Other variables, such as age, body weight, diet, and the presence of other genetic variants like those in the VKORC1 gene, also play major roles. Consequently, clinical management is always based on a combination of genetic information and real-time monitoring of a patient's clinical status.
Population Frequency
The frequency of the rs1057911 variant varies significantly across different ancestral populations. In European populations, the minor allele frequency (MAF) is typically observed between 0.04 and 0.08. In contrast, the variant is less common in East Asian populations, where the MAF generally ranges from 0.01 to 0.03. These differences highlight the importance of considering ancestry when evaluating the potential impact of pharmacogenetic variants. Because the prevalence of the *3 allele differs globally, the likelihood that a patient will require a dose adjustment based on this specific genetic marker is not uniform across all ethnic groups. Understanding these population-level trends helps clinicians anticipate the need for genetic testing or alternative dosing strategies in diverse patient populations.
What This Information Means for You
If you are aware of your status for the rs1057911 variant, it is essential to understand that this information is a tool for your healthcare provider, not a medical diagnosis. Genetic testing for pharmacogenomics is intended to help clinicians make more informed decisions about medication selection and initial dosing. It does not replace the need for regular clinical monitoring, such as blood tests to check your INR levels if you are taking warfarin. You should never change your medication dosage or stop taking a prescribed drug based on genetic test results without consulting your doctor or pharmacist. They are the only ones who can interpret these results in the context of your overall health, current medications, and clinical history. Always share your pharmacogenetic reports with your medical team to ensure your treatment plan is safe and personalized to your specific needs.
How common is this variant?
The rs1057911 variant has a minor allele frequency of approximately 0.04-0.08 in European populations and 0.01-0.03 in East Asian populations.
Frequently asked questions
Does having the rs1057911 variant mean I cannot take warfarin?
No, having this variant does not mean you cannot take warfarin. It simply means your body may process the medication more slowly, so your doctor may need to adjust your starting dose to ensure it is safe and effective for you.
Is genetic testing for CYP2C9 routine for everyone?
Genetic testing for CYP2C9 is not currently recommended as a routine test for the general population. It is typically considered by clinicians when a patient is starting a medication known to be affected by this gene, such as warfarin, to help guide initial dosing.
Can I use this information to choose my own medication dose?
Absolutely not. You should never adjust your medication dosage based on genetic information alone. Always consult with your physician or pharmacist, as they must consider your entire medical profile, including other medications and health conditions, before making any changes.
Are there other genes that affect warfarin dosing?
Yes, warfarin dosing is complex and influenced by multiple factors. The VKORC1 gene is another major genetic determinant that, along with CYP2C9, is frequently considered by clinicians when calculating an appropriate warfarin dose.
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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Get my report — $29Related variants in CYP2C9
Rare variant in the CYP2C9 gene potentially impacting enzyme activity and drug metabolism; clinical significance requires further validation.
Coding variant conferring the CYP2C9*3 allele (often mislabeled as *4 in older literature) with decreased enzymatic activity affecting clearance of drugs such as warfarin and phenytoin.
Missense mutation defining the CYP2C9*5 allele that dramatically lowers metabolic activity towards oral anticoagulants and anti-epileptic medications.
A rare variant in the CYP2C9 gene that may impact the metabolism of various clinical drugs.
The CYP2C9*2 variant (p.Arg144Cys) results in reduced enzymatic activity, significantly impacting the metabolism and required dosing of substrates such as warfarin and irbesartan.
The CYP2C9*3 allele significantly reduces enzyme activity, necessitating dose adjustments for warfarin and phenytoin.