CYP2C18 rs2860840: What Your Genotype Means
The rs2860840 variant is a genetic change located in the CYP2C18 gene, which is part of a cluster of enzymes responsible for metabolizing many common medications. It is frequently studied alongside other variants as part of a haplotype that may influence how the body processes drugs, though its clinical significance remains a subject of ongoing research.
What each genotype means
Typical metabolic profile
This genotype represents the absence of the T allele at this position. Research indicates that this variant is often studied in the context of the CYP2C:TG haplotype, and current evidence does not support using this specific genotype to predict drug metabolism or clinical outcomes. Please discuss any concerns regarding medication dosing with your clinician or pharmacist.
This genotype is common in many global populations, though it is less frequent in indigenous American cohorts where the T allele is highly prevalent.
Typical metabolic profile
Carrying one copy of the T allele is part of the CYP2C:TG haplotype, which has been investigated for potential effects on CYP2C19-mediated drug metabolism. However, current scientific consensus suggests there is insufficient evidence to conclude that this genotype significantly alters drug clearance or clinical response. Please discuss any concerns regarding medication dosing with your clinician or pharmacist.
This genotype is found across various ancestries and is frequently observed in admixed populations.
Typical metabolic profile
Carrying two copies of the T allele is associated with the CYP2C:TG haplotype. While some studies have explored whether this haplotype influences the metabolism of certain medications, recent clinical research has not found a consistent or significant impact on drug processing. Please discuss any concerns regarding medication dosing with your clinician or pharmacist.
This genotype is highly prevalent in indigenous American populations, where the T allele frequency can reach 0.96.
Understanding the rs2860840 Variant
The rs2860840 variant is a single nucleotide polymorphism (SNP) situated within the CYP2C18 gene. This gene is part of the CYP2C cluster on chromosome 10, a region critical for the production of cytochrome P450 enzymes. These enzymes are essential for the metabolism of a wide array of therapeutic drugs, including antidepressants, proton pump inhibitors, and antifungals. The rs2860840 variant is often analyzed in conjunction with another variant, rs11188059, to form what researchers call the 'CYP2C:TG' haplotype. Because these variants are located in non-coding regions of the gene, they do not change the structure of the protein itself. Instead, scientists investigate whether these variants act as regulatory switches that might increase or decrease the amount of enzyme produced by the body, potentially altering how quickly a person clears specific medications from their system.
The Role of the CYP2C Gene Cluster
The CYP2C gene cluster is a powerhouse of drug metabolism, housing genes like CYP2C8, CYP2C9, and CYP2C19, in addition to CYP2C18. While CYP2C19 is well-known for its role in activating or deactivating many clinical drugs, the specific contribution of CYP2C18 to drug metabolism is less clearly defined. Some research suggests that genetic variations in the CYP2C cluster might have a ripple effect, where changes in one gene influence the expression or activity of its neighbors. This has led to the hypothesis that the CYP2C:TG haplotype, which includes rs2860840, might be linked to 'ultrarapid' metabolism of certain drugs. However, this remains a complex area of study. Because these genes are located so close together on the chromosome, they are often inherited as a block, making it difficult for researchers to isolate the exact effect of a single SNP like rs2860840 from the rest of the cluster.
Research Evidence and Clinical Significance
Current scientific evidence regarding rs2860840 is mixed. Some early studies suggested that the presence of the T allele at this position might be associated with increased metabolic activity for certain CYP2C19 substrates, such as escitalopram. However, subsequent, more comprehensive studies—including those analyzing liver tissue samples and clinical pharmacokinetic data—have failed to find a consistent, significant impact on drug clearance. For instance, recent research evaluating the metabolism of omeprazole in diverse populations found no statistically significant association between the CYP2C:TG haplotype and drug metabolic ratios. Consequently, major pharmacogenetic organizations do not currently recommend testing for this variant to guide clinical dosing. The evidence is considered limited, and researchers emphasize that more functional validation is required before this variant can be used to inform medical decisions. It is currently viewed as a marker of interest for population genetics rather than a validated tool for clinical practice.
Population Frequency and Ancestry
One of the most notable features of rs2860840 is its striking variation in frequency across different global populations. The variant is particularly common in indigenous American cohorts, where the T allele frequency has been observed to reach as high as 0.96 in some groups. This is significantly higher than the frequencies observed in other global populations, such as those represented in the 1000 Genomes Project. This high prevalence in Native American populations has made the variant a focal point for researchers trying to understand why standard genotype-predicted metabolic phenotypes sometimes fail to match the actual drug-processing speeds observed in these individuals. By studying this variant, scientists hope to better understand the genetic architecture of drug metabolism in diverse populations, ensuring that future pharmacogenetic guidelines are inclusive and accurate for people of all ancestral backgrounds.
What This Information Means for You
If you have received information about your rs2860840 genotype, it is important to understand that this variant is not currently used to make clinical decisions about medication dosing. Because the scientific community has not reached a consensus on its functional impact, having a specific genotype does not necessarily mean you will experience a different response to any medication. You should never change your medication dosage or stop taking a prescribed drug based on genetic test results without consulting your healthcare provider. If you are concerned about how your body processes a specific medication, the best course of action is to discuss your concerns with your doctor or a clinical pharmacist. They can evaluate your clinical history, current medications, and other factors to provide personalized guidance. Genetic testing for pharmacogenomics is a rapidly evolving field, and your clinician is the best resource for interpreting how any genetic information applies to your specific health needs.
How common is this variant?
The rs2860840 T allele is highly prevalent in indigenous American populations, with frequencies ranging from 0.70 to 0.96, which is significantly higher than in other global populations.
Frequently asked questions
Is rs2860840 used to determine drug dosage?
No, rs2860840 is not currently used in clinical guidelines to determine drug dosage. Current evidence is insufficient to support its use in clinical practice.
Does the rs2860840 variant change how my body processes medicine?
While some research has explored this possibility, studies have not consistently shown that this variant significantly alters drug metabolism. More research is needed to understand its role.
Why is this variant so common in Native American populations?
The high frequency of this variant in indigenous American populations is a subject of ongoing study in population genetics. It is likely due to historical population dynamics and genetic drift.
Should I get tested for the CYP2C:TG haplotype?
There is currently no clinical recommendation to test for this haplotype. You should discuss any concerns about your medication response with your doctor or pharmacist.
Sources & further reading
Educational information only, last refreshed 11/2/2026. Not medical advice — these associations describe population statistics, not individual predictions.
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