CYP2C9 rs9332239: What Your Genotype Means
The rs9332239 variant is a genetic change located in the CYP2C9 gene that defines the CYP2C9*12 allele. It is primarily studied for its potential impact on how the body processes certain medications, particularly in populations of African ancestry.
What each genotype means
Normal enzyme activity
This genotype represents the most common form of the CYP2C9 gene, often referred to as the *1 allele. Individuals with this profile typically exhibit standard metabolism for medications processed by this enzyme, such as warfarin or phenytoin. 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 CYP2C9*12 variant, which is associated with decreased enzyme function. Research suggests this may lead to slower clearance of certain drugs like warfarin, potentially requiring dose adjustments to avoid side effects. Please discuss your medication management with your healthcare provider or pharmacist.
This genotype is rare in most populations, with the minor allele frequency reported at approximately 0.02 in individuals of African ancestry.
Significantly reduced enzyme activity
This genotype indicates you carry two copies of the CYP2C9*12 variant, which is linked to significantly reduced metabolism of specific medications. Because your body may process drugs like warfarin or phenytoin more slowly than average, there may be an increased risk of adverse effects at standard doses. Always consult with your clinician or pharmacist regarding your specific medication dosing needs.
This genotype is very rare and is primarily observed in individuals of African ancestry.
Understanding the rs9332239 Variant
The rs9332239 variant is a single nucleotide polymorphism (SNP) located on chromosome 10 within the CYP2C9 gene. In scientific literature, this specific genetic change is often referred to as the CYP2C9*12 allele. It involves a substitution where a cytosine (C) is replaced by a thymine (T) at a specific position in the DNA sequence, resulting in a change in the protein structure known as p.Pro489Ser. Because this variant is located in a gene responsible for drug metabolism, researchers investigate whether this change alters the efficiency with which the body breaks down various therapeutic compounds. While many SNPs are neutral, those in the CYP2C9 gene are of particular interest to pharmacogeneticists because they can influence the concentration of drugs in the bloodstream, potentially affecting both the efficacy and safety of standard medication doses.
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 found in the liver and are essential for the oxidative metabolism of approximately 15% of all commonly prescribed drugs. The CYP2C9 enzyme is responsible for breaking down a wide range of substances, including nonsteroidal anti-inflammatory drugs (NSAIDs) like ibuprofen, as well as more specialized medications such as the anticoagulant warfarin and the anticonvulsant phenytoin. When the CYP2C9 gene contains variants that reduce the enzyme's activity, the body may clear these medications more slowly than expected. This can lead to higher-than-intended levels of the drug in the blood, which may increase the risk of side effects. Understanding an individual's CYP2C9 status is a key component of precision medicine, helping clinicians tailor treatment plans to a patient's unique genetic profile.
Research and Clinical Evidence
Research into rs9332239 is categorized as having limited evidence regarding its clinical impact compared to more common variants like CYP2C9*2 or *3. Studies have explored the association between the CYP2C9*12 allele and the metabolism of drugs like warfarin and phenytoin, particularly in cohorts of African ancestry where this variant is more frequently observed. While some data suggests that carriers of certain CYP2C9 variants may require lower doses of these medications to avoid toxicity, the evidence for rs9332239 specifically is still evolving. It is important to note that drug response is complex and influenced by many factors, including other genetic variants, age, weight, diet, and concurrent medications. Because the evidence is limited, this variant is not currently the primary focus of standard clinical dosing algorithms, which typically prioritize more established markers. Always consult with a healthcare provider or pharmacist before making any changes to your medication regimen based on genetic information.
Population Frequency
The rs9332239 variant shows distinct patterns of distribution across different global populations. It is most frequently observed in individuals of African ancestry, with a minor allele frequency of approximately 0.02. In contrast, the variant is considered rare in European, East Asian, and other non-African populations. This ancestry-specific distribution highlights the importance of including diverse populations in genetic research to ensure that findings are applicable to all groups. Because the variant is relatively uncommon even within African populations, large-scale studies are often required to fully understand its functional consequences. Genetic testing services may report this variant, but it is essential to interpret these results within the context of your broader genetic background and clinical history, always under the guidance of a qualified medical professional.
What You Can Do With This Information
If you have received results indicating you carry the rs9332239 variant, it is important to approach this information as a piece of a much larger puzzle. Genetic testing provides data, but it does not constitute a medical diagnosis or a prescription instruction. You should never stop or change the dosage of any medication based on a genetic report without first speaking to your doctor or pharmacist. They are the only ones qualified to interpret how your specific genetic profile might interact with your current health needs and medications. If you are concerned about how you process a specific drug, consider asking your clinician if pharmacogenetic testing is appropriate for your situation. They can help you understand the clinical relevance of your results and determine if any adjustments to your treatment plan are necessary to ensure your safety and the effectiveness of your therapy.
How common is this variant?
The rs9332239 variant has a minor allele frequency of approximately 0.02 in African populations and is considered rare in other global ancestries.
Frequently asked questions
What is the CYP2C9*12 allele?
The CYP2C9*12 allele is a specific genetic variant defined by the presence of the T allele at the rs9332239 position. It is studied for its potential to reduce the activity of the CYP2C9 enzyme.
Does rs9332239 affect warfarin dosing?
Some research suggests that certain CYP2C9 variants can influence warfarin metabolism, but the evidence for rs9332239 is limited. Clinical dosing decisions for warfarin are typically based on established guidelines that prioritize more common variants.
Should I change my medication if I have this variant?
No. You should never change your medication or dosage based on genetic test results without consulting your doctor. Only a healthcare professional can determine if your genetic profile requires a change in your treatment plan.
Is rs9332239 common in all populations?
No, this variant is primarily found in individuals of African ancestry and is rare in other populations. Its frequency varies significantly depending on your genetic background.
Sources & further reading
Educational information only, last refreshed 9/17/2026. Not medical advice — these associations describe population statistics, not individual predictions.
Curious what your genotype is for rs9332239?
Upload a raw DNA file from 23andMe, AncestryDNA, MyHeritage, or FamilyTreeDNA and see this variant — plus thousands more — interpreted in your full report.
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.