SLC22A1 rs228269: Understanding Your Metformin Response Variant
The rs228269 variant is a genetic change located within the SLC22A1 gene, which provides instructions for making the OCT1 transporter protein. This variant is studied for its potential role in influencing how the body processes and responds to the common diabetes medication metformin.
What each genotype means
Typical OCT1 transporter activity
This genotype represents the most common form of the SLC22A1 gene in many populations. Research suggests that individuals with this profile typically maintain standard function of the OCT1 transporter, which is involved in the uptake of metformin into liver cells. Please discuss your medication response and any concerns about your treatment plan with your healthcare provider or pharmacist.
This is the most common genotype observed across most global populations.
Intermediate OCT1 transporter activity
Carrying one copy of the T allele may result in altered activity of the OCT1 transporter compared to those with two copies of the C allele. While some studies suggest this could influence how your body processes metformin, the clinical impact remains a subject of ongoing research and may vary significantly between individuals. Please consult your clinician or pharmacist regarding your specific medication dosing and response.
This genotype is found at varying frequencies depending on ancestral background, appearing in a significant portion of the population.
Potential reduced OCT1 transporter activity
This genotype is associated with a potential reduction in the function of the OCT1 transporter, which plays a role in the hepatic uptake of metformin. Scientific evidence regarding how this specific genotype affects individual glycemic control or side-effect profiles is mixed and limited. You should discuss your metformin therapy and any observed side effects with your healthcare provider to ensure your treatment remains appropriate for your needs.
This genotype is less common than the CC or CT genotypes in most studied populations.
What is the rs228269 Variant?
The rs228269 variant is a single nucleotide polymorphism (SNP) found within the SLC22A1 gene. In genetics, a SNP represents a variation at a single position in the DNA sequence. This specific variant is located in a region of the genome that codes for the organic cation transporter 1 (OCT1) protein. Because this protein is essential for moving various substances into cells, researchers investigate whether changes in the DNA sequence at this location might alter the structure or function of the resulting transporter. By studying such variants, scientists aim to understand why individuals may experience different outcomes when taking the same medication, a field known as pharmacogenomics.
The Role of the SLC22A1 Gene
The SLC22A1 gene encodes the OCT1 protein, which acts as a gatekeeper for many substances entering cells, particularly in the liver. For patients prescribed metformin to manage blood glucose levels, OCT1 is critical because it facilitates the uptake of the drug into liver cells, where it exerts its primary therapeutic effects. When the OCT1 transporter functions optimally, metformin can effectively enter the liver to help regulate glucose production. If the function of this transporter is reduced due to genetic variation, it may theoretically impact the amount of medication that reaches its target site, potentially leading to differences in how well the drug controls blood sugar or how it is tolerated by the patient.
Research and Evidence Strength
Research into SLC22A1 variants and metformin response is an active area of study, though the evidence for any single variant like rs228269 remains limited. While some studies have identified associations between various SLC22A1 polymorphisms and changes in metformin pharmacokinetics—such as the drug's concentration in the blood or its impact on HbA1c levels—these findings are often inconsistent across different populations. Many studies are small in scale, and results frequently do not reach statistical significance after adjusting for multiple testing. Consequently, while the biological mechanism linking OCT1 to metformin is well-established, the clinical utility of using rs228269 to predict an individual's specific response to metformin is not yet supported by robust, large-scale clinical evidence.
Population Frequency
The rs228269 variant is considered a common genetic variation. Frequency data from global genomic databases indicate that this SNP is present at varying frequencies across different ancestral populations. Because it is common, many individuals carry at least one copy of the variant allele. However, the specific distribution of genotypes can differ significantly between groups, such as those of African, European, or Asian descent. These differences highlight the importance of considering ancestral background when interpreting genetic data, as the prevalence of specific alleles can influence the overall genetic landscape of a population.
What This Information Means for You
It is important to understand that genetic variants like rs228269 are only one piece of a very complex puzzle. Factors such as diet, lifestyle, kidney function, and other medications play a much larger role in how a person responds to metformin than any single genetic variant. You should never use information about your genotype to make decisions about your medication, such as changing your dose or stopping treatment. If you are curious about how your genetics might influence your health or your response to a prescribed drug, the best course of action is to discuss this with your healthcare provider or a clinical pharmacist. They can provide context based on your full medical history and current clinical guidelines.
How common is this variant?
The rs228269 variant is a common polymorphism found across global populations, with genotype frequencies varying by ancestral background.
Frequently asked questions
Can I use a genetic test to predict if metformin will work for me?
Currently, there is no standard clinical genetic test for metformin response. While research into genes like SLC22A1 is ongoing, clinical decisions are based on blood tests like HbA1c and kidney function rather than genetic markers.
Does the rs228269 variant cause diabetes?
No, the rs228269 variant is not a cause of diabetes. It is a genetic variation being studied for its potential influence on how the body processes certain medications, not for the development of the disease itself.
Should I ask my doctor for a pharmacogenomic test?
You can certainly ask your doctor about pharmacogenomics, but be aware that testing for metformin response is not currently part of routine clinical practice. Your doctor will prioritize established clinical markers to manage your treatment.
Where can I find more information about SLC22A1?
You can find reliable information on the SLC22A1 gene and its function through resources like MedlinePlus Genetics or the National Center for Biotechnology Information (NCBI) Gene database.
Sources & further reading
Educational information only, last refreshed 9/23/2026. Not medical advice — these associations describe population statistics, not individual predictions.
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Also known as OCT1 p.Met420del, this loss-of-function deletion directly diminishes hepatic uptake and glycemic response to metformin in patients with type 2 diabetes.
This SNP is investigated alongside rs72552763 for its role in modulating glycemic response and HbA1c levels in diabetic patients treated with metformin.
A missense variant in OCT1 that impairs organic cation cellular uptake, altering clinical responsiveness and gastrointestinal tolerance to metformin.
A well-characterized loss-of-function variant (M420del) in the organic cation transporter 1 (OCT1) that reduces hepatic uptake of metformin and other basic drugs, modulating therapeutic efficacy and side effects.
Located in the organic cation transporter gene SLC22A1, this intronic variant has been associated with altered glycemic response and tolerability to metformin therapy.
This missense variant (OCT1 Met420del) leads to reduced cellular uptake of metformin and other organic cations, influencing glycemic response.