ABCB1 rs1045645: What Your Genotype Means
The rs1045645 variant is a common genetic change located within the ABCB1 gene, which provides instructions for making the P-glycoprotein transporter. This protein acts as a cellular pump, and variations in the gene are studied for their potential influence on how the body absorbs and processes certain medications.
What each genotype means
Common reference genotype
This is the most frequently observed genotype for this variant in many global populations. Research into this variant, often referred to as C3435T, explores its potential influence on the expression of the P-glycoprotein transporter, though clinical evidence remains limited and inconsistent. Please discuss any concerns regarding medication response or dosing with your clinician or pharmacist.
This is the most common genotype found across most major ancestral populations.
Heterozygous genotype
You carry one copy of each allele for this variant. Studies have investigated whether this genotype correlates with altered drug absorption or clinical outcomes for certain therapies, but findings are mixed and not definitive. Always consult with your healthcare provider or pharmacist before making changes to your medication regimen.
This genotype is frequently observed in diverse populations worldwide.
Variant homozygous genotype
You carry two copies of the variant allele. Some research suggests this genotype may be associated with differences in the function or expression of the ABCB1 transporter compared to the reference genotype, though the clinical significance of these findings is currently debated and limited. Please consult your clinician or pharmacist to understand how this might relate to your specific pharmacological treatments.
This genotype is present at varying frequencies across global populations, being less common than the CC genotype in many groups.
Understanding the rs1045645 Variant
The rs1045645 variant is a single nucleotide polymorphism (SNP) found within the ABCB1 gene, also known as the multidrug resistance 1 (MDR1) gene. SNPs are the most common type of genetic variation among people, representing a difference in a single DNA building block, or nucleotide. In the context of rs1045645, researchers track whether an individual carries a cytosine (C) or a thymine (T) at this specific position in the genetic code. Because this variant is located in a gene responsible for critical transport functions, scientists have long investigated whether these small changes in DNA sequence lead to measurable differences in how the body handles various substances, including therapeutic drugs. It is important to note that while this SNP is frequently studied, it is just one of many variations within the complex ABCB1 gene, and its presence does not automatically dictate a specific health outcome or drug response.
The Role of the ABCB1 Gene
The ABCB1 gene encodes a protein called P-glycoprotein (P-gp). This protein functions as an ATP-dependent efflux transporter, essentially acting as a biological pump that moves various molecules across cell membranes. P-glycoprotein is expressed in many tissues throughout the body, including the lining of the intestines, the blood-brain barrier, the liver, and the kidneys. By pumping substances out of cells, P-gp plays a vital role in protecting the body from toxins and xenobiotics. Because it is so widespread, P-gp also influences the pharmacokinetics—how the body absorbs, distributes, metabolizes, and excretes—of many common medications. When the ABCB1 gene contains variants like rs1045645, researchers hypothesize that the resulting P-glycoprotein might be produced at different levels or function with different efficiency. This could theoretically alter the concentration of a drug in the bloodstream or at its target site, potentially impacting both the efficacy of the treatment and the risk of side effects.
Research and Clinical Evidence
Research into rs1045645 has explored its association with various clinical outcomes, particularly in the fields of oncology and pharmacology. Studies have examined whether this variant influences how patients respond to chemotherapy or other drug therapies by affecting drug accumulation in cells. However, the evidence linking rs1045645 to specific clinical outcomes remains limited and often inconsistent across different studies. While some research suggests potential correlations between ABCB1 variants and drug toxicity or efficacy, other large-scale studies have failed to find significant, reproducible effects. The complexity of drug response, which is influenced by many genes, environmental factors, and individual health history, makes it difficult to isolate the impact of a single SNP. Consequently, there is currently no broad clinical consensus or standardized guideline that recommends using rs1045645 testing to guide routine medical dosing. The scientific community continues to investigate these associations, but the clinical utility of this specific variant remains a subject of ongoing academic debate rather than established medical practice.
Population Frequency and Interpretation
The rs1045645 variant is considered common, meaning it appears frequently across diverse human populations. Allele frequencies can vary significantly depending on ancestral background, which is a standard observation in human genomics. Because this variant is widespread, it is not considered a rare mutation but rather a normal part of human genetic diversity. When interpreting information about this SNP, it is crucial to understand that having a particular genotype is not a diagnosis. Genetic associations are statistical observations made across large groups of people and do not necessarily predict an individual's personal response to a medication. If you are curious about how your genetic profile might relate to your health or specific treatments, the most appropriate step is to consult with your physician or a pharmacist. They can provide context based on your full medical history and current clinical guidelines, ensuring that any decisions regarding your care are based on comprehensive, evidence-based information rather than isolated genetic data.
How common is this variant?
The rs1045645 variant is common across global populations, though the specific frequency of the C and T alleles varies significantly between different ancestral groups.
Frequently asked questions
Does rs1045645 mean I will have a bad reaction to medication?
No, having a specific genotype for rs1045645 does not guarantee a particular reaction to any medication. Drug response is complex and influenced by many factors, including other genes, diet, and overall health.
Should I get tested for the ABCB1 rs1045645 variant?
There is currently no standard clinical recommendation to test for this variant to guide medication dosing. You should discuss any concerns about your medication response with your doctor or pharmacist.
Is rs1045645 the same as the MDR1 gene?
rs1045645 is a specific genetic variant located within the ABCB1 gene, which is also historically known as the MDR1 gene. The gene provides the instructions for the P-glycoprotein transporter.
Can I use this information to change my drug dosage?
Absolutely not. You should never change your medication dosage or stop taking a prescribed drug based on genetic information without consulting your healthcare provider.
Sources & further reading
Educational information only, last refreshed 9/24/2026. Not medical advice — these associations describe population statistics, not individual predictions.
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This SNP is linked to variations in the pharmacokinetics of drugs that are substrates for the ABCB1 transporter protein.
Nonsynonymous variant (Ala893Ser/Thr) in ABCB1/MDR1 altering P-glycoprotein transporter kinetics and plasma concentrations of drugs such as digoxin, fexofenadine, and tacrolimus.
Synonymous polymorphism in the ABCB1 (MDR1) transporter gene influencing substrate drug efflux and systemic drug exposure.
Synonymous exon 26 variant in ABCB1 linked to altered mRNA stability and variable response to multiple cardiovascular medications.
A variant in the ABCB1 gene associated with potential differences in drug transport across the blood-brain barrier, though clinical impact on antidepressant efficacy remains debated.
This SNP is part of a tight linkage block in the ABCB1 gene that may influence drug response, though studies on its clinical utility in depression have yielded conflicting results.