XRCC1 rs1799782: What Your Genotype Means
The genetic variant rs1799782 is a missense single nucleotide polymorphism in the XRCC1 gene, resulting in an amino acid substitution from arginine to tryptophan (p.Arg194Trp). The XRCC1 protein acts as a critical molecular scaffold in base-excision repair, helping cells mend single-strand DNA breaks. Research has primarily investigated whether this variant influences individual therapeutic response and toxicity profiles in patients undergoing platinum-based chemotherapy.
What each genotype means
Typical DNA repair capacity
This genotype represents the most common form of the XRCC1 gene, which encodes the arginine (Arg) amino acid at position 194. Research suggests this version of the protein may function differently in DNA repair compared to the variant form, and individuals with this genotype have been observed to have different clinical outcomes when treated with platinum-based chemotherapy. Please discuss your treatment plan and any potential medication responses with your clinician or pharmacist.
This is the most common genotype in European populations, though it is less frequent in East and South Asian populations.
Altered DNA repair potential
This genotype indicates you carry one copy of the variant allele, which results in a substitution of tryptophan (Trp) for arginine (Arg) at position 194 of the XRCC1 protein. Some studies suggest that individuals with this genotype may experience different responses or toxicity levels when undergoing platinum-based chemotherapy compared to those with the C/C genotype. Please consult with your healthcare provider or pharmacist regarding how this genetic information may relate to your specific medical care.
This genotype is found in a significant portion of the population, with higher prevalence in East and South Asian ancestries compared to European populations.
Variant DNA repair potential
This genotype means you carry two copies of the variant allele, which encodes tryptophan (Trp) at position 194 of the XRCC1 protein. Research has associated this genotype with altered DNA repair efficiency and potential differences in clinical outcomes or treatment response for patients receiving platinum-based chemotherapy. Because these associations can be complex and vary by study, please discuss the implications of this result with your clinician or pharmacist.
This genotype is less common than the heterozygous form, with higher frequencies observed in East and South Asian populations compared to European populations.
What Is rs1799782 and Where Is It Located?
The single nucleotide polymorphism (SNP) designated rs1799782 is located on human chromosome 19q13.2 within the XRCC1 gene (X-ray repair cross-complementing protein 1). This variant represents a cytosine-to-thymine (C>T) substitution in the coding sequence of the gene. In protein terms, the change translates to an amino acid substitution at codon 194, where an arginine residue is replaced by a tryptophan residue (often written as p.Arg194Trp or Arg194Trp). This specific modification occurs within the first linker region of the XRCC1 scaffold protein. Bioinformatic tools like SIFT predict that substituting the basic, polar arginine with the bulky, non-polar aromatic amino acid tryptophan may alter local structural dynamics and functional interactions with complementary DNA repair enzymes. Despite these predictions, biological outcomes can vary significantly depending on cellular context and genetic background.
The Biological Role of the XRCC1 Gene
The XRCC1 gene encodes an essential scaffolding protein that coordinates the base-excision repair (BER) pathway. Whenever DNA sustains damage from oxidative stress, alkylating compounds, or reactive cellular metabolites, the base-excision repair system removes the altered base and seals the single-strand break. XRCC1 does not possess dedicated catalytic enzymatic activity of its own; instead, it coordinates repair by binding directly to multiple critical repair proteins, including DNA polymerase beta (Pol-β), Poly(ADP-ribose) polymerase 1 (PARP-1), and DNA Ligase III (LIG-3). By recruiting these molecular partners to damaged genomic sites, XRCC1 ensures swift, high-fidelity restoration of chromosome integrity. If structural variations in XRCC1 alter its interaction with these repair partners, cellular capacity to resolve DNA damage may decrease, rendering cells more sensitive to DNA-damaging environmental exposures and therapeutic drugs.
Pharmacogenomics and Chemotherapy Research
Platinum-based antineoplastic drugs, such as cisplatin and carboplatin, kill cancer cells primarily by causing crosslinks and oxidative lesions in DNA. Because XRCC1 facilitates the repair of related DNA lesions, researchers have evaluated rs1799782 as a predictive pharmacogenomic biomarker. The PharmGKB database currently categorizes rs1799782 at evidence level 3, which denotes preliminary or limited clinical evidence. Several meta-analyses and clinical cohort studies, particularly in East Asian non-small cell lung cancer (NSCLC) cohorts, have reported that carriers of the minor T allele (Trp) exhibited improved objective response rates and favorable progression-free survival compared to C/C homozygotes. The hypothesized mechanism is that diminished repair efficiency leaves cancer cells less capable of overcoming platinum-induced damage. However, findings across Caucasian and other ancestral populations have produced conflicting or neutral results, leaving clinical utility unproven and controversial.
Population Distribution and Ancestral Differences
Allele frequencies for rs1799782 display prominent ancestral stratification across global human populations. In European and African populations, the minor T allele is relatively uncommon, typically presenting with a minor allele frequency (MAF) ranging from roughly 0.05 to 0.11. In contrast, the variant is substantially more prevalent across Asian ancestries. In East Asian and South Asian populations, the frequency of the T allele frequently spans 0.25 to 0.35, meaning that a significant portion of individuals in these communities carry at least one copy of the variant. Because the majority of statistically significant associations between rs1799782 and platinum-based chemotherapy response have been documented in Asian cohorts, ancestral genetic architecture likely modulates how this variant interacts with overall genomic repair mechanisms.
Clinical Limitations and Next Steps
Despite decades of academic investigation, professional pharmacogenomic guidelines such as the Clinical Pharmacogenetics Implementation Consortium (CPIC) do not recommend using rs1799782 to guide chemotherapy drug selection or dosing. The statistical associations identified in observational studies have not translated into validated, routine clinical utility, largely due to conflicting outcome reports across differing cancers, dosing regimens, and ancestries. A direct-to-consumer genetic test report showing this SNP should not be interpreted as a diagnostic result or a prediction of cancer susceptibility. Patients receiving chemotherapy or preparing for treatment must never modify their medical plans, dosing, or therapeutic decisions based on personal genotype data. Any concerns regarding potential chemotherapy efficacy or adverse toxicities should always be discussed directly with an oncologist, clinical geneticist, or specialized pharmacotherapy pharmacist.
How common is this variant?
The minor T allele occurs at a frequency of approximately 5% to 11% in individuals of European and African descent, while it is considerably more frequent in East Asian and South Asian populations, where allele frequencies range between 25% and 35%.
Frequently asked questions
Can the XRCC1 rs1799782 genotype predict if my chemotherapy will work?
No, this genetic variant cannot reliably predict individual treatment outcomes. Although some observational research associates the T allele with altered response to platinum-based drugs, evidence is classified as limited (PharmGKB level 3). Major clinical bodies do not recommend using this SNP to choose chemotherapy regimens.
Does having the T allele of rs1799782 mean I have a higher risk of cancer?
Carrying the T allele does not indicate that you will develop cancer. Numerous large-scale meta-analyses evaluating XRCC1 rs1799782 have found mixed, weak, or non-significant associations across various cancer types, indicating it is not a validated standalone diagnostic marker.
What is the biological difference between the C and T alleles for rs1799782?
The C allele codes for arginine at amino acid position 194 of the XRCC1 protein, which is the baseline form found most commonly worldwide. The T allele changes this amino acid to tryptophan, which computational analyses suggest may slightly alter the scaffold protein's ability to coordinate repair enzymes during base-excision repair.
Should I share my rs1799782 results with my oncologist?
You can share your complete genetic testing results with your care team if you choose, but oncologists do not currently alter treatment plans based on rs1799782. Always speak with your doctor or clinical pharmacist before drawing any conclusions about medication efficacy or side-effect risks.
Sources & further reading
Educational information only, last refreshed 9/5/2026. Not medical advice — these associations describe population statistics, not individual predictions.
Curious what your genotype is for rs1799782?
Upload a raw DNA file from 23andMe, AncestryDNA, MyHeritage, or FamilyTreeDNA and see this variant — plus thousands more — interpreted in your full report.
Get my report — $29