CYP2C19 rs4244285: What Your Genotype Means
The rs4244285 variant is a specific genetic change in the CYP2C19 gene that creates a non-functional enzyme. It is widely studied in pharmacogenomics because it can alter how individuals metabolize common medications, including clopidogrel and certain antidepressants.
What each genotype means
Normal enzyme activity
This genotype is associated with normal function of the CYP2C19 enzyme, which is responsible for processing certain medications. Individuals with this profile are typically classified as normal metabolizers, meaning they process drugs like clopidogrel at standard rates. Please discuss your medication dosing and any concerns with your clinician or pharmacist.
This is the most common genotype in most global populations, though frequencies vary significantly by ancestry.
Reduced enzyme activity
This genotype includes one copy of the loss-of-function variant, often referred to as the *2 allele, which can lead to reduced activity of the CYP2C19 enzyme. You may be classified as an intermediate metabolizer, which can affect how your body processes specific drugs like clopidogrel or certain antidepressants. Please discuss your medication options and potential dosing adjustments with your clinician or pharmacist.
Carried by a significant portion of the population, with frequencies ranging from approximately 15% in Europeans to over 30% in some East Asian populations.
Significantly reduced enzyme activity
This genotype contains two copies of the loss-of-function variant, which is associated with a poor metabolizer phenotype. This may result in a significantly impaired ability to activate prodrugs like clopidogrel, potentially reducing their clinical effectiveness. Please consult with your clinician or pharmacist to discuss how this genetic profile may influence your treatment plan.
This genotype is less common than the heterozygous form, occurring in a smaller percentage of the population across most ancestries.
What is rs4244285?
The rs4244285 variant is a single nucleotide polymorphism (SNP) located within the CYP2C19 gene. Specifically, it involves a G to A transition at position 681 in the gene's sequence. In the scientific literature, this specific change is the defining marker for the CYP2C19*2 allele. This genetic alteration creates an aberrant splice site during the process of turning DNA instructions into proteins. Because of this splicing error, the resulting mRNA is defective, leading to the production of a truncated, non-functional enzyme. Because the enzyme cannot perform its normal work, individuals carrying this variant may experience differences in how their bodies process, or 'biotransform,' various drugs that rely on this enzyme for clearance or activation.
The Role of the CYP2C19 Gene
The CYP2C19 gene provides instructions for making an enzyme that belongs to the cytochrome P450 family. These enzymes are primarily found in the liver and are responsible for breaking down a wide variety of substances, including many prescription medications. CYP2C19 is particularly important for the metabolism of proton pump inhibitors (used for acid reflux), certain antidepressants, and the anti-platelet drug clopidogrel. When the gene functions normally, the enzyme helps convert prodrugs—medications that are inactive until processed—into their active forms, or it helps clear active drugs from the body. When a person carries loss-of-function variants like rs4244285, the enzyme's activity is significantly reduced or absent, which can lead to lower levels of active drug in the blood or, conversely, higher levels of drugs that should have been cleared.
Research and Clinical Associations
Research into rs4244285 is extensive, particularly in the field of pharmacogenomics. The variant is strongly associated with a 'poor metabolizer' phenotype when present on both copies of the gene. Clinical studies have shown that patients with this genotype may have reduced platelet inhibition when taking standard doses of clopidogrel, which is a critical concern for patients undergoing cardiac procedures like stenting. Similarly, the variant is linked to altered clearance rates for various antidepressants and proton pump inhibitors. While the evidence for these associations is robust, the clinical impact can vary based on the specific drug and the individual's overall genetic profile. Because of this, medical guidelines often suggest that clinicians consider genotype information when selecting medications or determining appropriate dosages to ensure both safety and efficacy.
Population Frequency
The frequency of the rs4244285 variant varies significantly across different ancestral groups. Data from large-scale genomic studies indicate that the minor allele frequency is approximately 15% in European populations and 17% in African populations. The variant is notably more common in East Asian populations, where the frequency ranges from 30% to 35%. These differences mean that the prevalence of 'poor metabolizer' status—where an individual carries two copies of the loss-of-function allele—is much higher in some parts of the world than in others. Understanding these population-level differences is a key component of global pharmacogenomics research, as it helps healthcare systems anticipate the need for personalized dosing strategies in diverse patient populations.
What You Can Do With This Information
If you have received results regarding your CYP2C19 genotype, it is important to view this information as a tool for communication with your healthcare provider. This variant does not mean you will necessarily have a negative reaction to a medication, but it does provide your doctor with valuable context for making informed prescribing decisions. You should never change your medication dosage or stop taking a prescribed drug based on genetic test results without consulting your physician or pharmacist. They are the only ones who can interpret these results in the context of your full medical history, other medications you may be taking, and your current health status. If you are concerned about how your body processes a specific drug, bring your genetic report to your next appointment to discuss whether a dosage adjustment or an alternative medication might be appropriate for you.
How common is this variant?
The minor allele frequency is approximately 15% in Europeans, 17% in Africans, and 30-35% in East Asians.
Frequently asked questions
Does having the rs4244285 variant mean I am allergic to my medication?
No, this variant is not an allergy. It relates to how your liver enzymes process a drug, which can affect how much of the active medication reaches your bloodstream.
Can I change my medication dose based on my CYP2C19 genotype?
You should never change your medication dose on your own. Always discuss your genetic results with your doctor or pharmacist, as they must consider many factors beyond just your genetics.
Is this the only variant that affects CYP2C19?
No, there are many other variants in the CYP2C19 gene, such as *3 and *17, that can also influence how the enzyme functions. A comprehensive genetic test often looks at multiple variants.
Where can I find more information about pharmacogenomics?
You can visit resources like PharmGKB or the CPIC guidelines website for detailed, evidence-based information on how specific genes affect drug response.
Sources & further reading
Educational information only, last refreshed 10/26/2026. Not medical advice — these associations describe population statistics, not individual predictions.
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Defines the CYP2C19*17 increased function allele, conferring rapid or ultrarapid metabolism for CPIC-actionable drugs including clopidogrel, PPIs, and SSRIs.
Variant in the CYP2C19 locus associated with altered metabolism of clopidogrel and proton-pump inhibitors.
Defines the CYP2C19*8 loss-of-function variant (c.358T>C, p.Trp120Arg) which results in no enzymatic activity and impaired metabolism of CYP2C19 substrates.
Defines the non-functional CYP2C19*3 null allele resulting from a premature stop codon, leading to poor metabolism of drugs such as clopidogrel, escitalopram, and proton pump inhibitors.
Defines the CYP2C19*4 allele caused by an ATG start codon alteration that abolishes translation, resulting in reduced or absent drug metabolism capacity.
Known as CYP2C19*3, this premature stop codon (c.636G>A, p.Trp212Ter) results in a complete loss-of-function phenotype for clopidogrel and antidepressant metabolism.