CYP2C9 rs1057910: Understanding Your Drug Metabolism
The CYP2C9 rs1057910 variant is a well-studied genetic change that alters how your body processes specific medications. Because this variant significantly reduces the activity of the CYP2C9 enzyme, it is a critical factor in personalized medicine for drugs such as warfarin and phenytoin.
What each genotype means
Normal enzyme activity
This genotype is considered the reference or wild-type form of the CYP2C9 gene. Individuals with this profile typically exhibit normal metabolism for medications processed by the CYP2C9 enzyme, such as warfarin, phenytoin, and certain sulfonylureas.
This is the most common genotype across most global populations.
Reduced enzyme activity
This genotype, often referred to as carrying one CYP2C9*3 allele, is associated with a reduced ability to metabolize certain drugs compared to the A/A genotype. Research indicates this may lead to slower clearance of medications like warfarin, which can influence dosing requirements. Please discuss your medication dosing and potential side effects with your clinician or pharmacist.
Carried by approximately 6-12% of people in many European and South Asian populations, though it is less common in African and East Asian populations.
Significantly reduced enzyme activity
This genotype, representing the homozygous CYP2C9*3 state, is associated with a significant reduction in the activity of the CYP2C9 enzyme. Individuals with this profile may clear drugs like warfarin, phenytoin, and glipizide much more slowly than others, which can increase the risk of drug accumulation and side effects. It is essential to consult with your healthcare provider or pharmacist regarding any medications you are prescribed, as dose adjustments may be necessary.
This genotype is relatively rare, occurring in less than 1% of many populations, though frequencies vary by ancestry.
What is rs1057910 and Where is it Located?
The variant rs1057910, often referred to in clinical literature as the CYP2C9*3 allele, is a single nucleotide polymorphism (SNP) located within the CYP2C9 gene on chromosome 10. Specifically, this variant involves a change in the DNA sequence where an adenine (A) is replaced by a cytosine (C). This seemingly small change—a single letter alteration in the vast human genome—has profound functional consequences. When this SNP occurs, it causes an amino acid substitution (isoleucine to leucine at position 359) in the resulting protein structure. This alteration is not just a random marker; it directly impacts the physical shape and, consequently, the chemical efficiency of the CYP2C9 enzyme. Because the enzyme’s job is to act as a biological processor for various substances, changing its structure changes its performance, making rs1057910 a key focus for pharmacogenomics research.
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 active in the liver, where they act as the body’s detoxification and metabolism team. Their main responsibility is to break down, or "metabolize," a wide array of compounds, including toxins, dietary substances, and approximately 10-20% of all commonly prescribed clinical medications. By chemically modifying these drugs, the CYP2C9 enzyme prepares them to be eliminated from the body. When the gene functions normally (often designated as *1), the enzyme efficiently clears drugs from the bloodstream at a predictable rate. However, when variants like rs1057910 are present, the enzyme's metabolic capacity is significantly diminished. This creates a "bottleneck" effect, where the medication remains in the system for longer than intended, potentially leading to higher-than-expected drug levels and an increased risk of adverse side effects if standard doses are administered.
Research and Clinical Evidence
The scientific evidence linking rs1057910 to altered drug metabolism is classified as strong by international pharmacogenomics consortia. Extensive studies, including those curated by the Clinical Pharmacogenetics Implementation Consortium (CPIC) and PharmGKB, demonstrate that individuals carrying the C allele metabolize substrates like warfarin (a blood thinner) and phenytoin (an anti-seizure medication) much more slowly than those without it. Because of this, clinical guidelines often recommend specific dose adjustments for carriers of this variant to prevent drug toxicity or ineffective treatment. The GWAS Catalog and other large-scale genetic databases highlight this SNP as a primary determinant of inter-individual variability in drug response. While the evidence is robust, it is important to remember that drug metabolism is complex; other genetic factors, environmental influences, and individual health status also play roles in how a person responds to medication.
What This Information Means for You
Knowing your status for rs1057910 can be a powerful tool for your healthcare team, but it is not a diagnostic tool for general health. This information is specifically intended to help your doctor or pharmacist choose the safest and most effective dose if you are ever prescribed medications metabolized by CYP2C9. If you receive results for this variant, do not make any changes to your current medications. Instead, bring your genetic report to your clinician. They are the only ones qualified to interpret these results in the context of your medical history, other medications you may be taking, and your overall health. This information is a guide for personalized dosing, not a substitute for professional medical advice. Always discuss pharmacogenomic testing results with a healthcare provider who can help translate genetic data into safe, actionable clinical decisions.
How common is this variant?
The rs1057910 variant is most prevalent in populations of European ancestry, where the C allele frequency typically ranges from 5% to 10%. It is notably less common in East Asian and African populations.
Frequently asked questions
Does having the rs1057910 variant mean I cannot take certain medications?
No, it does not mean you cannot take these medications. It simply means that your body may process them differently, which may require your doctor to adjust your dosage to keep you safe and ensure the medication works correctly.
Should I get tested for this specific variant?
Clinical testing for rs1057910 is generally only recommended if you are being considered for treatment with specific drugs like warfarin or phenytoin. You should discuss the necessity of this testing with your physician.
Will this variant affect how I process all medications?
No, this variant specifically affects the CYP2C9 enzyme. It does not affect every medication, only those that rely on this specific enzyme pathway for metabolism.
Is this genetic variant hereditary?
Yes, like all variants in your genome, rs1057910 is inherited from your parents. You receive one copy from your mother and one from your father, which determines your genotype.
Sources & further reading
Educational information only, last refreshed 9/15/2026. 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.
Defining the CYP2C9*3 (p.Ile359Leu) allele, this variant markedly decreases enzymatic activity, requiring reduced dosages for warfarin and phenytoin to prevent toxicity.