SLC22A1 rs2276039: What Your Genotype Means
rs2276039 is a common single nucleotide polymorphism in the SLC22A1 gene, which encodes the organic cation transporter 1 (OCT1). This missense variant alters an amino acid in the transporter protein and has been studied for its potential effects on the hepatic uptake and pharmacokinetics of substrate medications like metformin. Current clinical evidence remains limited and variable, meaning it serves as an educational pharmacogenomic marker rather than a definitive clinical guide.
What each genotype means
Typical transporter function
This genotype represents the most common form of the SLC22A1 gene, often referred to as the wild-type or reference sequence. Research suggests that individuals with this genotype typically exhibit standard activity of the OCT1 transporter, which is responsible for the hepatic uptake of medications like metformin. Please discuss your medication response and any dosing concerns with your clinician or pharmacist.
This is the most common genotype, found in the majority of individuals across most global populations.
Intermediate transporter activity
This genotype indicates you carry one copy of the Met408Val variant. Studies suggest that this variant may influence the efficiency of the OCT1 transporter in moving certain drugs, such as metformin, into the liver. Because this is a complex trait, please consult your healthcare provider or pharmacist regarding how this may relate to your specific medication therapy.
This heterozygous genotype is common, occurring in a significant portion of individuals, particularly in European populations.
Reduced transporter activity
This genotype indicates you carry two copies of the Met408Val variant. Research indicates that this variant can lead to reduced function of the OCT1 transporter, which may affect the pharmacokinetic profile of substrates like metformin. As individual responses to medication vary, please discuss your treatment plan and potential dosing adjustments with your clinician or pharmacist.
This homozygous variant genotype is observed at a lower frequency than the heterozygous state, but remains a common polymorphism in many populations.
Understanding rs2276039 and the SLC22A1 Gene
The single nucleotide polymorphism rs2276039 is located in the SLC22A1 gene on human chromosome 6. SLC22A1 provides instructions for making organic cation transporter 1, commonly abbreviated as OCT1. OCT1 is an integral membrane transport protein abundantly expressed on the sinusoidal membrane of hepatocytes in the liver, as well as along the basolateral surfaces of intestinal enterocytes. It functions as an influx gateway, actively facilitating the movement of diverse positively charged molecules, endogenous metabolites, and pharmaceutical compounds from the bloodstream into liver tissue. The rs2276039 variant involves a nucleotide transition that results in a substitution of methionine with valine at amino acid position 408 (often referenced in scientific literature as Met408Val or c.1222A>G). Because of its position in the transporter's structural framework, researchers have focused on whether this change impacts how effectively the protein docks and transports therapeutic substrates.
Pharmacogenomics and Metformin Response
A primary area of research surrounding SLC22A1 variants involves the pharmacokinetics and clinical efficacy of metformin, a frontline oral medication prescribed for type 2 diabetes. Because metformin relies heavily on organic cation transporters like OCT1 for absorption in the gut and delivery to its major site of metabolic action in the liver, changes in OCT1 efficiency can theoretically influence systemic drug clearance and therapeutic response. Some pharmacogenetic investigations have associated the variant allele with subtle alterations in metformin uptake, peak circulating drug concentrations, or variations in initial glycemic response, such as reductions in glycated hemoglobin (HbA1c). However, the overall strength of clinical evidence connecting rs2276039 directly to drug efficacy or intolerance is classified as limited. Findings across clinical trials and observational cohorts have yielded mixed results, frequently confounded by co-inherited variants, lifestyle factors, renal function, and differences in study designs.
Global Frequencies and Population Patterns
Unlike rare pathogenic mutations that cause classical single-gene disorders, rs2276039 is a very frequent polymorphism found throughout human populations across the globe. In individuals of European ancestry, the minor or variant allele occurs at a substantial frequency, typically observed between 0.35 and 0.45. This high prevalence means that heterozygous carriers and homozygous variant individuals are exceedingly common rather than rare exceptions. Similar or moderately varying allele distributions have been documented across South Asian, East Asian, and other continental ancestry cohorts. The evolutionary persistence of this polymorphism indicates that it does not disrupt basic physiological survival. However, because baseline frequencies and background genetic architectures vary substantially across diverse ancestral backgrounds, clinical associations observed in one ancestral group cannot be universally generalized without comprehensive multi-ethnic validation.
Clinical Realities and Medical Interpretation
While discovering your rs2276039 genotype provides interesting insight into individual drug-transporter genetics, it cannot be used to diagnose any disease or dictate medical choices. Major clinical pharmacogenomics consortia, such as CPIC, have not established formal actionable dosing guidelines based solely on this single variant, reflecting the limited and inconsistent nature of the current scientific data. Metformin efficacy and tolerance are complex multifactorial traits driven by renal excretion, drug transporters such as MATE1 and OCT2, organ health, diet, and patient adherence. Consumers should never adjust, start, or discontinue any prescription medication based on personal genetic testing reports. Any questions regarding glycemic control, medication side effects, or drug selection should always be addressed directly with a treating physician, endocrinologist, or licensed clinical pharmacist.
How common is this variant?
rs2276039 is a high-frequency polymorphism across global populations, with the minor variant allele observed at approximately 35% to 45% in European cohorts and widely documented in Asian and other ancestral populations.
Frequently asked questions
Does having rs2276039 mean metformin will not work for me?
No, having one or two copies of this variant does not mean metformin will fail. Clinical studies have shown mixed and limited associations with drug response, and many individuals carrying the variant manage their blood glucose successfully on standard regimens.
Can rs2276039 cause type 2 diabetes?
No, rs2276039 is classified as a pharmacogenomic variant affecting drug transport rather than a causative disease mutation. Type 2 diabetes development is influenced by a broad combination of lifestyle, metabolic factors, and hundreds of polygenic risk loci.
Should I change my medication dose based on my genotype?
You should never alter or stop your prescription medication based on commercial genetic test results. There are currently no clinical guidelines recommending dosage modifications for rs2276039, and any medication decisions must be made under the supervision of your healthcare provider.
Why do some studies show different effects for this variant?
Differences in study outcomes often occur because metformin response involves multiple biological systems, including kidney excretion, other transporter genes, and patient lifestyle. Additionally, variations in cohort sample sizes, definitions of clinical response, and ancestral genetic backgrounds can lead to divergent results.
Sources & further reading
Educational information only, last refreshed 9/8/2026. Not medical advice — these associations describe population statistics, not individual predictions.
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Functional non-synonymous variant (M420del) in the organic cation transporter OCT1, significantly impacting the hepatic uptake of various drugs including metformin.
An intronic variant in the organic cation transporter gene associated with altered metformin side-effect profiles.
A variant associated with the occurrence of gastrointestinal side effects in metformin users.
Variant in SLC22A1 (OCT1) associated with altered metformin transport and glycemic response.
Also known as OCT1 p.Met420del, this loss-of-function deletion diminishes hepatic uptake and glycemic response to metformin in patients with type 2 diabetes.
A missense variant in OCT1 that impairs organic cation cellular uptake, altering clinical responsiveness and gastrointestinal tolerance to metformin.