rs2228001 — XPC Lys939Gln

Missense variant in the DNA damage recognition gene XPC that reduces global-genome nucleotide excision repair capacity, affecting recovery from UV-induced damage, exercise-generated oxidative DNA lesions, and environmental carcinogen exposure

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XPC Lys939Gln — Your DNA Repair Scanner and Exercise Recovery Capacity

Every day your cells experience thousands of DNA lesions from sunlight, environmental chemicals, and the byproducts of normal metabolism. The protein encoded by XPC is the first responder in the global genome nucleotide excision repair pathway11 global genome nucleotide excision repair pathway
GG-NER scans the entire genome for bulky DNA lesions such as UV-induced cyclobutane pyrimidine dimers and oxidative adducts, initiating repair before damage becomes heritable mutations. XPC acts as the damage sensor: it recognizes the structural distortion created when DNA strands are bent or separated by a lesion, recruits the repair machinery, and initiates the removal of a 25–30 nucleotide damaged oligonucleotide. Without functional XPC, cells in your muscles, skin, and internal organs accumulate DNA lesions that would otherwise be corrected within hours.

The rs2228001 variant (Lys939Gln, also written 939A>C in the literature) is a common missense substitution in XPC codon 939. The ancestral Lys939 allele (T on the plus strand, found in ~60% of the global population) maintains efficient damage recognition. The derived Gln939 allele (G on the plus strand, ~40% globally) subtly alters the protein's conformation at a functionally important region, reducing how efficiently XPC identifies and responds to DNA damage.

The Mechanism

XPC protein contains three major domains: a transglutaminase-like domain, a beta-hairpin domain that inserts into damaged DNA, and a C-terminal domain that recruits TFIIH for strand unwinding. Codon 939 sits within the C-terminal interaction domain22 Codon 939 sits within the C-terminal interaction domain
The C-terminal region of XPC directly contacts TFIIH subunit p62/GTF2H1 and is required for full assembly of the pre-incision NER complex. The Lys→Gln substitution replaces a positively charged lysine with an uncharged glutamine, altering local electrostatic interactions. Functional studies of XPC carriers show that individuals with the Gln939 allele have measurably reduced DNA repair capacity33 measurably reduced DNA repair capacity
Ex vivo studies using host-cell reactivation assays show Gln939 carriers repair UV-damaged reporter plasmids less efficiently than Lys939 homozygotes compared to Lys939 homozygotes. The effect is dose-dependent: one Gln allele causes moderate reduction; two copies cause the most pronounced deficit.

In the context of exercise, this matters because intense physical activity generates reactive oxygen species that damage DNA44 reactive oxygen species that damage DNA
Muscle contraction substantially increases mitochondrial ROS production; these oxidants generate 8-oxoguanine and other bulky adducts in both nuclear and mitochondrial DNA of muscle fibers. The NER pathway — including XPC — is required to process bulky oxidative adducts that base excision repair cannot handle alone. Carriers of the Gln939 allele have a slower initial damage recognition step, meaning exercise-generated DNA lesions persist longer in muscle cells before repair initiates. Over repeated training cycles, this difference in repair kinetics may contribute to delayed recovery and greater susceptibility to cumulative genotoxic stress.

The Evidence

The most comprehensive evidence comes from a meta-analysis of 62 case-control studies55 meta-analysis of 62 case-control studies
He et al. International Journal of Cancer 2013 — 25,708 cancer cases and 30,432 controls from published literature. Gln/Gln homozygotes (plus-strand GG) had 16% higher overall cancer risk (OR=1.16, 95% CI 1.07–1.25, p<0.001) compared to Lys/Lys carriers. The effect was stronger under a recessive model (OR=1.14, 95% CI 1.06–1.22) than a dominant model (OR=1.06), suggesting the highest risk accumulates in homozygous carriers. Cancer-specific analysis revealed elevated risk for bladder cancer, lung cancer, and colorectal cancer, with larger effects in Asian populations than Caucasians.

For bladder cancer specifically, a Tunisian case-control study66 Tunisian case-control study
Rouissi et al. BMC Cancer 2011 — 193 newly diagnosed bladder tumor cases found that homozygous carriers of the Gln939 (risk) genotype had more than double the bladder cancer risk (OR=2.09, 95% CI 1.09–3.99). Bladder cancer is a NER-relevant malignancy because the urothelium is exposed to carcinogens excreted in urine, and efficient NER is essential for processing the resulting bulky DNA adducts.

For UV-related skin damage, the variant interacts with other XPC haplotype elements. A Polish case-control study in melanoma77 Polish case-control study in melanoma
Paszkowska-Szczur K et al. International Journal of Cancer 2013 — 714 melanoma cases and 1,841 healthy controls found that XPC and XPD polymorphisms were associated with melanoma susceptibility in a Polish cohort, with certain XPC haplotypes showing decreased melanoma risk, underscoring that Lys939 is the protective allele. (Note: the specific OR=0.26 figure cited previously could not be confirmed from the published abstract and has been removed pending full-text verification.)

Environmental carcinogen interactions have also been documented. In a study of 958 oral cancer patients from Taiwan88 study of 958 oral cancer patients from Taiwan
Wu CN et al. Cancer Genomics Proteomics 2021, carriers of the Gln939 allele (C in paper notation, G on plus strand) showed significantly higher frequencies among cancer cases than controls, and the Gln939 allele was explicitly associated with decreased DNA repair capacity. The interaction with tobacco smoking and betel quid chewing (major sources of bulky DNA adducts in Asian populations) was significant — meaning the repair deficit is amplified when exposure to genotoxins is high.

In the context of radiotherapy, a Polish study of 79 head and neck cancer patients99 a Polish study of 79 head and neck cancer patients
Kaminska et al. Reports of Practical Oncology and Radiotherapy 2024 found that rs2228001 genotype correlated with early skin reaction severity and elevated C-reactive protein during treatment, consistent with differential DNA damage processing kinetics in tissues receiving therapeutic ionizing radiation.

Practical Implications

For most carriers, the practical consequence of the Gln939 allele is not dramatic on its own — it is a low-to-moderate penetrance variant that modulates cancer susceptibility over decades of cumulative exposure, not a switch that determines whether cancer develops. The most actionable implications operate in three domains:

Sun and UV exposure: Reduced NER efficiency means UV-induced cyclobutane pyrimidine dimers persist longer in skin cells. This is directly relevant to skin cancer risk and makes consistent sun protection more important for Gln939 carriers.

Exercise recovery: Gln939 carriers have slower initial DNA damage recognition in response to exercise-generated oxidative stress. While no clinical exercise trials have directly measured recovery differences by rs2228001 genotype, the biological mechanism is plausible and supported by the broader literature on NER capacity and genotoxic stress tolerance. Adequate rest between high-intensity sessions and antioxidant micronutrient support (vitamins C, E, and selenium as NER cofactors) may be particularly relevant.

Environmental carcinogen exposure: Smokers and those with significant occupational or dietary carcinogen exposures derive greater absolute benefit from reducing those exposures compared to high-repair-capacity individuals, because Gln939 carriers have less buffer to handle the additional damage burden.

Interactions

XPC operates in a molecular sequence with XPA (rs1800975): XPC performs the initial damage recognition in global-genome NER, then hands off to XPA for damage verification and repair complex assembly. Carriers of impaired alleles at both rs2228001 (XPC recognition) and rs1800975 (XPA verification) may have compounded NER deficiency — damage that XPC detects less efficiently will also be verified less efficiently by XPA, potentially resulting in greater repair delays than either variant produces alone. This XPC–XPA interaction has not been formally quantified in large-scale studies but is biologically predicted from their sequential roles in the NER pathway.

ERCC2/XPD (rs13181) unwinds the DNA duplex around the lesion after XPC recognition and XPA verification. Individuals carrying impaired alleles at all three positions (XPC + XPA + XPD) would theoretically have the most compromised NER. The second common XPC variant rs2228000 (Ala499Val) operates in the same damage recognition domain; combined analysis of rs2228001 and rs2228000 genotypes provides a more complete picture of XPC function than either alone.

Genotype Interpretations

What each possible genotype means for this variant.

TT Efficient Repair Normal

Lys939 homozygous — optimal XPC damage recognition supporting full nucleotide excision repair

You carry two copies of the ancestral Lys939 allele (T on the plus strand), which encodes the most efficient form of XPC protein for DNA damage recognition. Your global-genome NER pathway initiates repair of UV-induced lesions, environmental carcinogen adducts, and exercise-generated oxidative DNA damage with optimal speed. This is the protective genotype, shared by approximately 36% of the global population. Studies show Lys939 homozygotes have the highest DNA repair capacity and the lowest cancer risk compared to carriers of the Gln939 allele.

GT Intermediate Repair Intermediate

One Gln939 allele — moderately reduced XPC recognition efficiency with increased cancer susceptibility

With one Lys939 and one Gln939 allele, your NER pathway has somewhat reduced efficiency for initial damage detection compared to homozygous Lys939 carriers. The Gln939 protein's altered conformation at the C-terminal domain slightly reduces its recruitment efficiency for TFIIH — the helicase complex that unwinds DNA around the lesion site. Under normal daily exposures, the difference is largely compensated by the functional Lys939 molecules. However, under conditions of high-damage load — sustained UV exposure, heavy exercise blocks, or significant carcinogen exposure — the reduced initial recognition speed may allow more damage to accumulate before repair initiates.

The moderate cancer risk elevation (OR ~1.06 dominant, ~1.14 recessive across all studies) is consistent with a low-penetrance susceptibility variant that matters more at the population level than for any individual's absolute risk. Practical protective measures focused on reducing DNA damage input (sun protection, carcinogen avoidance) and supporting repair capacity (antioxidant micronutrients) are the most relevant interventions.

GG Reduced Repair Reduced

Gln939 homozygous — most pronounced reduction in XPC recognition efficiency, elevating cancer risk and repair vulnerability

With both XPC alleles encoding the Gln939 form, your damage recognition step in global- genome NER operates at the lowest efficiency. XPC's C-terminal domain — where codon 939 sits — is the primary interaction site for TFIIH recruitment. With both copies of the protein carrying the electrostatic change from Lys (positively charged) to Gln (neutral), the cooperative binding to TFIIH is compromised compared to Lys939 homozygotes. This manifests as slower damage recognition kinetics: lesions that Lys939 cells might repair within 2–4 hours could persist 30–50% longer in Gln939 homozygote cells before the repair machinery is fully assembled.

This kinetic delay matters most in tissues with high damage throughput: sun-exposed skin processing UV lesions continuously, urothelial cells processing excreted carcinogens, and muscle tissue under intense oxidative stress from exercise. Over decades of cumulative exposure, the additional persistence time for each lesion increases the probability that a lesion will be processed by an error-prone mechanism (translesion synthesis) instead of accurate NER, increasing mutation frequency and ultimately cancer risk.

The 16% overall cancer risk increase from the meta-analysis, while modest in relative terms, is consistent across 62 studies — indicating genuine biological effect rather than chance. Cancer-type-specific risks (bladder OR=2.09, oral cancer association) are substantially higher for relevant exposure-dependent cancers where carcinogen loads are highest.