ABCB1 rs1045642: What Your Genotype Means
The rs1045642 variant is a common genetic change located within the ABCB1 gene, which provides instructions for making a protein called P-glycoprotein. This protein acts as a cellular pump, and variations in this gene are associated with differences in how the body transports and clears various medications.
What each genotype means
Typical P-glycoprotein expression
This genotype is often considered the reference or wild-type form of the ABCB1 gene. Research into how this genotype affects medication transport is extensive but often conflicting, with some studies suggesting higher P-glycoprotein activity compared to the T allele. Please discuss any concerns regarding your medication response or potential side effects with your clinician or pharmacist.
This is a common genotype found across all major global populations.
Intermediate P-glycoprotein expression
Carrying one copy of the T allele may result in different P-glycoprotein activity levels compared to those with the CC genotype. Scientific literature on this variant is mixed, and the clinical impact on drug clearance varies significantly depending on the specific medication and the individual. Always consult your healthcare provider before making changes to your prescribed treatment plan.
This heterozygous genotype is frequently observed in diverse populations worldwide.
Reduced P-glycoprotein expression
Some research indicates that this genotype is associated with lower P-glycoprotein expression and reduced transport of certain medications, which may influence how your body processes specific drugs. Because findings are inconsistent across different studies and medications, this result should not be used to predict clinical outcomes on its own. Please review your medication regimen with your doctor or pharmacist to ensure your dosing is appropriate for you.
This genotype is common, appearing in a significant portion of individuals across various ancestral backgrounds.
Understanding the rs1045642 Variant
The rs1045642 variant, often referred to in scientific literature as C3435T, is a single-nucleotide polymorphism (SNP) found within the ABCB1 gene. A SNP represents a variation at a single position in the DNA sequence. In the case of rs1045642, the DNA can contain either a cytosine (C) or a thymine (T) at this specific location. This variant is situated in a region of the gene that influences the production and function of P-glycoprotein. Because this gene is highly active in tissues that act as barriers—such as the lining of the intestines, the blood-brain barrier, and the liver—changes here can have broad implications for how substances, including therapeutic drugs, move through the body.
The Role of the ABCB1 Gene
The ABCB1 gene encodes P-glycoprotein, a member of the ATP-binding cassette transporter superfamily. P-glycoprotein functions as an efflux pump, meaning it actively transports molecules out of cells. By pumping substances out of cells and back into the bloodstream or into excretory pathways, P-glycoprotein plays a critical role in protecting the body from toxins and regulating the absorption and distribution of many medications. When the expression or efficiency of this pump is altered due to genetic variations like rs1045642, the concentration of certain drugs in the blood or tissues may change. This can potentially affect both the efficacy of a treatment and the likelihood of experiencing side effects, as the drug may remain in the system for a shorter or longer duration than expected.
Research and Clinical Associations
Research into rs1045642 has explored its impact on a wide range of medications, including digoxin, certain statins, and various antidepressants. Some studies suggest that individuals with the TT genotype may have lower P-glycoprotein expression, which could lead to reduced drug efflux and potentially higher drug concentrations in the body. However, the evidence is complex and often mixed. While some clinical studies have observed associations between this genotype and altered drug responses, others have found no statistically significant impact, or have noted that the effect varies depending on the specific drug, the patient's ancestry, and other environmental factors. Because of this variability, the clinical utility of testing for this variant remains a subject of ongoing investigation rather than a standard diagnostic tool for most medications.
Population Frequency
The rs1045642 variant is considered common, with the minor allele frequency typically ranging between 30% and 50% across most major global populations. This means that a significant portion of the general population carries at least one copy of the T allele.
What This Information Means for You
If you have received results regarding your rs1045642 genotype, it is important to understand that this information is not a medical diagnosis and does not predict your personal response to any specific medication with certainty. Genetic factors are only one piece of a much larger puzzle that includes your age, weight, diet, other medications you may be taking, and your overall health status. You should never make changes to your prescribed medications or dosages based on genetic test results without first consulting your healthcare provider or a pharmacist. These professionals are best equipped to interpret your genetic information in the context of your complete medical history and to guide you toward the safest and most effective treatment plan for your individual needs.
How common is this variant?
The rs1045642 variant is common across all major populations, with the T allele appearing in approximately 30-50% of individuals.
Frequently asked questions
Does the rs1045642 genotype mean I will have a bad reaction to my medication?
No, having a specific genotype does not guarantee a particular reaction to a medication. Many factors influence how your body processes drugs, and genetic variants are only one part of that process.
Should I ask my doctor for a test for this variant?
Genetic testing for this variant is not currently standard practice for most medications. You should discuss your concerns about medication efficacy or side effects with your doctor, who can determine if testing is appropriate for your specific situation.
Is rs1045642 the same as C3435T?
Yes, rs1045642 is the official reference SNP ID (rsID) for the variant commonly referred to in older scientific literature as C3435T.
Can I change my genotype to improve my health?
No, your genotype is determined at birth and cannot be changed. However, knowing your genetic profile can help your healthcare provider make more informed decisions about your medical care.
Sources & further reading
Educational information only, last refreshed 9/30/2026. Not medical advice — these associations describe population statistics, not individual predictions.
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This variant is studied for its influence on the pharmacokinetics of immunosuppressive drugs like cyclosporine and tacrolimus in transplant patients.
Synonymous variant (c.3435C>T) in ABCB1 linked to altered P-glycoprotein expression and multi-drug transporter pharmacokinetics.
Nonsynonymous variant in ABCB1 altering P-glycoprotein transporter kinetics.
This SNP is linked to variations in the pharmacokinetics of drugs that are substrates for the ABCB1 transporter protein.
A variant associated with potential differences in drug absorption and clinical outcomes in patients undergoing specific pharmacological therapies.
Synonymous polymorphism in the ABCB1 (MDR1) transporter gene influencing substrate drug efflux and systemic drug exposure.