What you carry at this position in your DNA and what research says about it.
DNA Repair and Cancer: 6/10 evidence, 55 publications.
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Sample genotype (not yours): G/G
Typical DNA Repair and Baseline Cancer Risk
Standard DNA repair efficiency keeps the risk of several cancers at baseline. Serum urate levels may be slightly higher than other genotypes.
What this genotype means: Typical DNA repair efficiency; Baseline breast and thyroid cancer risk; Slightly higher serum urate levels.
Sample genotype (not yours): A/A
Higher Breast and Thyroid Cancer Risk
Reduced DNA repair efficiency is linked to a higher risk of triple-negative breast cancer and thyroid cancer. Response to several chemotherapy drugs may be altered.
What this genotype means: Reduced DNA repair efficiency; Higher risk of triple-negative breast cancer; Higher risk of thyroid cancer.
Sample genotype (not yours): G/A
Typical Cancer Risk with Enhanced Chemotherapy Response
Baseline risk for breast and thyroid cancers is maintained. Response to certain platinum-based chemotherapy treatments may be improved.
What this genotype means: Typical DNA repair efficiency; Baseline breast and thyroid cancer risk; Better response to platinum chemotherapies.
Gene function and biological role
Gene Function: The XRCC3 gene encodes a crucial protein involved in repairing double-strand breaks in DNA through homologous recombination [1]. This pathway is essential for maintaining genomic stability and preventing the accumulation of mutations that can lead to cancer [2]. Although some databases map this region to the KLC1 gene, the functional impact of this specific variant is heavily characterized within the XRCC3 DNA repair pathway [1]. Proper functioning of this gene ensures that cells can accurately repair DNA damage caused by environmental factors like radiation or chemicals [2].
Variant Impact: This coding variant, also known as Thr241Met, results in a threonine-to-methionine amino acid substitution in the XRCC3 protein [1]. This structural change can alter the enzyme's stability and its interaction with other proteins in the homologous recombination repair complex [1]. Consequently, the variant affects how efficiently cells repair DNA double-strand breaks [2]. These alterations in DNA repair capacity have been linked to varying susceptibilities to several cancers and differences in chemotherapy drug sensitivity [1] [3].
Key Insight: The same genetic variant that increases the risk of certain cancers can also make tumor cells more sensitive to platinum-based chemotherapy.
Location: XRCC3. Chromosome 14 · 14q32.33 · 103.7 Mb
Estimated prevalence by population
Global 50.1%; European 39.0%; African 62.6%; East Asian 87.3%; South Asian 58.7%; Americas 54.9%; Ashkenazi 34.5%; Finnish 50.7%; Middle Eastern 38.3%; Amish 32.4%.
Estimated GG genotype frequency.
Global 40.3%; European 46.9%; African 33.1%; East Asian 12.2%; South Asian 35.9%; Americas 38.4%; Ashkenazi 48.5%; Finnish 41.0%; Middle Eastern 47.2%; Amish 49.0%.
Estimated GA genotype frequency.
Global 9.6%; European 14.1%; African 4.4%; East Asian 0.4%; South Asian 5.5%; Americas 6.7%; Ashkenazi 17.1%; Finnish 8.3%; Middle Eastern 14.5%; Amish 18.6%.
Estimated AA genotype frequency.
Showing effects for G/G genotype
Cancer & Oncology
Breast Cancer
Breast Cancer. Evidence: 4/10. Source: PMID 26543082. Typical Risk.
Thyroid & Endocrine Cancers
Thyroid Cancer. Evidence: 4/10. Source: PMID 31374908. Typical Risk.
Pharmacogenomics
Chemotherapy Response
Platinum Chemotherapy Response. Evidence: 5/10. Source: PMID 27248474. Typical Response.
Cardiovascular & Metabolic
Gout & Uric Acid
Uric Acid Levels. Evidence: 6/10. Source: PMID 38658550. Higher Levels.
Showing effects for A/A genotype
Breast Cancer. Evidence: 4/10. Source: PMID 26543082. ~3x Higher Risk.
Thyroid Cancer. Evidence: 4/10. Source: PMID 31374908. Increased Risk.
Platinum Chemotherapy Response. Evidence: 5/10. Source: PMID 27248474. Stronger Response.
Uric Acid Levels. Evidence: 6/10. Source: PMID 38658550. Lower Levels.
Showing effects for G/A genotype
Uric Acid Levels. Evidence: 6/10. Source: PMID 38658550. Typical Levels.
What this genotype means for the people who carry it
Sample genotype: GG (Homozygous)
Carrying two copies of the major G allele results in the standard threonine amino acid at position 241 of the XRCC3 protein [1]. This configuration maintains typical DNA double-strand break repair efficiency, keeping the baseline risk for breast and thyroid cancers stable [1] [2]. However, large-scale genetic studies associate the G allele with slightly elevated serum urate levels [3]. In the context of cancer treatment, this genotype is associated with a typical response to platinum-based chemotherapies [4]. Some studies also suggest a typical survival profile during standard colorectal cancer regimens [5].
Typical DNA repair efficiency; Baseline breast and thyroid cancer risk; Slightly higher serum urate levels.
Sample genotype: AA (Homozygous)
Carrying two copies of the minor A allele results in the methionine amino acid at position 241, which can reduce the efficiency of DNA double-strand break repair [1]. This compromised repair capacity is linked to an approximately threefold higher risk of triple-negative breast cancer in certain populations [1]. Additionally, meta-analyses show a significant association with an increased risk of thyroid cancer [2]. In oncology treatments, this genotype is associated with a better response to platinum-based therapies [3]. However, it is also linked to poorer responses or decreased survival with other agents like cisplatin, docetaxel, and irinotecan [4].
Reduced DNA repair efficiency; Higher risk of triple-negative breast cancer; Higher risk of thyroid cancer; Altered chemotherapy response.
Sample genotype: GA (Heterozygous)
Having one copy of the threonine-encoding G allele and one copy of the methionine-encoding A allele maintains typical DNA repair capacity [1]. This balance keeps the risk of developing triple-negative breast cancer and thyroid cancer at typical baseline levels [1] [2]. Interestingly, clinical studies indicate that this heterozygous profile is associated with a better response to platinum-based chemotherapy drugs [3]. However, some research suggests a slightly higher likelihood of radiation-induced side effects, such as rectal bleeding, when undergoing radiation therapy for prostate cancer [4]. Serum urate levels are typically intermediate or standard [5].
Typical DNA repair efficiency; Baseline breast and thyroid cancer risk; Better response to platinum chemotherapies.
Variants with shared genetic architecture
rs1799794 · XRCC3 Gene · Chr 14 · Chemotherapy Toxicity
rs16857609 · DIRC3 Gene · Chr 2 · Cancer Risk
rs180177132 · PALB2 Gene · Chr 16 · Hereditary Cancer Risk
Large-scale cross-ancestry genome-wide meta-analysis of serum urate.
Content updated August 2026.
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