CYP2C9 rs9332131: Understanding the CYP2C9*6 Null Allele
The rs9332131 variant is a specific genetic change in the CYP2C9 gene that defines the *6 allele. This variant is associated with a complete loss of catalytic activity in the resulting enzyme, which can impact how the body processes certain medications.
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 genotype typically possess fully functional enzyme activity for metabolizing medications like 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 inactive CYP2C9*6 allele, which is characterized by an 818delA frameshift mutation. Research suggests this may lead to reduced metabolism of certain drugs, potentially requiring lower doses to avoid toxicity. Please consult your healthcare provider or pharmacist regarding how this may influence your specific medication management.
This genotype is rare, occurring primarily in individuals of African ancestry and is largely absent in other populations.
What is the rs9332131 Variant?
The rs9332131 variant is a single nucleotide polymorphism (SNP) located within the CYP2C9 gene on chromosome 10. In scientific literature, this specific variant is widely recognized as the CYP2C9*6 allele. It is characterized by a deletion of an adenine nucleotide, specifically an 818delA frameshift mutation. This type of genetic change is significant because it alters the reading frame of the gene's instructions, typically leading to a non-functional protein. Because the resulting enzyme cannot perform its normal chemical tasks, individuals carrying this variant may experience differences in how their bodies metabolize specific substances. It is classified as a null allele, meaning it produces no active enzyme product, which distinguishes it from other variants that might only partially reduce enzyme function.
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 the metabolism of a wide variety of substances, including many common prescription medications. In the liver, the CYP2C9 enzyme plays a critical role in breaking down drugs such as warfarin, which is used to prevent blood clots, as well as certain non-steroidal anti-inflammatory drugs (NSAIDs) and phenytoin. By converting these drugs into inactive forms or metabolites, the enzyme helps the body clear them from the system. When the gene is functioning normally, the enzyme maintains a steady balance of drug levels in the blood. However, when a person inherits a variant like rs9332131, the enzyme's ability to process these medications is completely abolished, which can lead to higher-than-expected concentrations of the drug in the body.
Research and Clinical Associations
Research into rs9332131 has primarily focused on its impact on pharmacogenomics, particularly regarding warfarin therapy. Because the CYP2C9*6 allele results in a total loss of enzyme activity, individuals who carry this variant may require lower doses of medications that are normally cleared by this enzyme to avoid potential toxicity or adverse effects. The evidence for this association is considered significant in the context of clinical pharmacology, as it helps explain why some patients experience unexpected drug responses. However, because this variant is rare, large-scale clinical data is more limited compared to more common variants like *2 or *3. Studies have highlighted that failing to account for such specific alleles in diverse populations can lead to inaccurate dosing predictions. As with all pharmacogenomic findings, this information is intended for research and educational purposes; any decisions regarding medication dosing must be made in consultation with a qualified clinician or pharmacist.
What You Can and Cannot Do With This Information
Understanding your genetic profile regarding the CYP2C9 gene can provide valuable context about your potential response to certain medications. If you have access to genetic testing results that include this variant, you can use this information to have a more informed conversation with your healthcare provider. You can ask your doctor or pharmacist if your specific genotype might influence the metabolism of any medications you are currently taking or may be prescribed in the future. What you cannot do is use this information to self-diagnose or adjust your medication dosages on your own. Genetic variants are only one piece of a complex puzzle that includes your age, weight, diet, and other health conditions. Never stop or change a prescribed medication based on genetic data without professional medical guidance, as doing so could pose serious health risks.
How common is this variant?
The rs9332131 variant is rare, with a minor allele frequency of approximately 0.005 to 0.01 in individuals of African ancestry. It is considered absent or extremely rare in other global populations.
Frequently asked questions
What does it mean if I have the CYP2C9*6 allele?
Having the *6 allele means you carry a genetic variant that prevents the production of a functional CYP2C9 enzyme. This can affect how your body processes certain drugs, potentially requiring dose adjustments.
Is the rs9332131 variant common?
No, this variant is quite rare. It is primarily found in individuals of African ancestry and is very uncommon or absent in most other populations.
Does this variant affect all medications?
No, it only affects medications that are specifically metabolized by the CYP2C9 enzyme, such as warfarin, phenytoin, and certain NSAIDs. It does not affect the metabolism of drugs processed by other enzymes.
Should I get tested for this variant?
Genetic testing for pharmacogenomics is typically recommended by a doctor if you are starting a medication known to be affected by CYP2C9, such as warfarin. You should discuss the necessity of such testing with your healthcare provider.
Sources & further reading
Educational information only, last refreshed 9/19/2026. 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.