rs1805794 — NBN E185Q

NBN E185Q — Your DNA Double-Strand Break Repair Sensor

Every day, your cells sustain tens of thousands of DNA lesions from normal metabolism, environmental exposures, and replication errors. Most are single-strand nicks that are easily patched. But the most dangerous lesions are double-strand breaks (DSBs)¹¹ double-strand breaks (DSBs)
A complete break through both strands of the DNA helix. Left unrepaired, DSBs cause chromosomal rearrangements, deletions, or cell death. Even a single unrepaired DSB can trigger apoptosis., which sever both strands of the helix simultaneously. The protein encoded by the NBN gene (also known as NBS1, or nibrin) is the molecular sensor that detects these breaks and initiates the repair cascade.

NBN forms the MRN complex²² MRN complex
A trimeric complex of MRE11, RAD50, and NBN (NBS1) that is the first responder to DNA double-strand breaks. MRE11 provides nuclease activity, RAD50 bridges broken DNA ends, and NBN recruits the complex to damage sites and activates ATM kinase signaling. together with MRE11 and RAD50. This complex is the first responder at DSB sites: it recognizes the break, tethers the broken ends, activates the ATM checkpoint kinase, and channels repair through either homologous recombination³³ homologous recombination
Error-free repair that uses the sister chromatid as a template. Preferred in S/G2 phase when a template is available. or non-homologous end joining⁴⁴ non-homologous end joining
Faster but error-prone repair that directly ligates broken ends. Used throughout the cell cycle.. Beyond DSB repair, the MRN complex maintains telomere integrity, enables immunoglobulin class switching, and coordinates cell cycle checkpoints.

The rs1805794 variant causes a glutamic acid-to-glutamine substitution at position 185 (E185Q), located within the BRCT1 domain⁵⁵ BRCT1 domain
BRCA1 C-terminal domain -- a phosphoprotein-binding module found in many DNA damage response proteins. In NBN, the tandem FHA-BRCT domains mediate interaction with gamma-H2AX at DSB sites and recruit the BASC (BRCA1-associated genome surveillance complex). of the NBN protein. This domain is critical for recruiting the MRN complex to DSB sites through interaction with phosphorylated histone H2AX (gamma-H2AX) and BRCA1.

The Mechanism

The E185Q substitution replaces a negatively charged glutamic acid with an uncharged glutamine in the BRCT1 domain. This alters the electrostatic surface that mediates protein-protein interactions at DNA damage sites. Functional studies by Fang et al.⁶⁶ Functional studies by Fang et al.
Fang W et al. The functional polymorphism of NBS1 p.Glu185Gln is associated with an increased risk of lung cancer in Chinese populations. Mutat Res, 2014 demonstrated that cells carrying the Gln185 variant exhibited significantly more DNA breaks after X-ray exposure compared to cells with wild-type Glu185, and lymphocytes from variant carriers showed greater chromosomal damage following ionizing radiation. This indicates a measurable reduction in DSB repair efficiency.

The variant also showed a gene-environment interaction with medical ionizing radiation exposure (interaction p = 0.015), suggesting that the repair deficiency becomes more consequential under conditions of increased DNA damage load.

The Evidence

The cancer risk evidence has been evaluated across multiple large meta-analyses. The first comprehensive meta-analysis⁷⁷ first comprehensive meta-analysis
Lu M et al. Association between the NBS1 E185Q polymorphism and cancer risk: a meta-analysis. BMC Cancer, 2009 pooled 16 studies with 9,734 cancer cases and 10,325 controls. Carriers of GC/CC genotypes (containing the Gln185 variant) had a modest but significant 1.06-fold elevated overall cancer risk (OR 1.06, 95% CI 1.00-1.12), with a slightly stronger effect in Caucasians (OR 1.07, 95% CI 1.01-1.14).

An updated meta-analysis of 48 studies⁸⁸ updated meta-analysis of 48 studies
He YZ et al. NBS1 Glu185Gln polymorphism and cancer risk: update on current evidence. Tumor Biol, 2014 covering 17,159 cases and 22,002 controls found no significant association with overall cancer risk but identified increased risk for specific cancer types: leukemia, nasopharyngeal carcinoma, and urinary system cancers.

The strongest site-specific evidence is for lung cancer. A meta-analysis of six lung cancer studies⁹⁹ meta-analysis of six lung cancer studies
Wang L et al. Association between the NBS1 Glu185Gln polymorphism and lung cancer risk. Mol Biol Rep, 2013 comprising 2,348 cases and 2,401 controls found OR 1.21 (95% CI 1.07-1.37) in the dominant model, with the effect driven by Asian populations (OR 1.22, 95% CI 1.06-1.41).

For prostate cancer, a Portuguese case-control study¹⁰¹⁰ Portuguese case-control study
Silva J et al. DNA repair system and prostate cancer progression: the role of NBS1 polymorphism (rs1805794). DNA Cell Biol, 2012 of 425 patients found that GG carriers had nearly two-fold increased risk for advanced prostate disease (OR 1.87, 95% CI 1.26-2.79). In renal cell carcinoma, male patients carrying the variant C allele showed a nearly four-fold increase in 5-year mortality risk¹¹¹¹ nearly four-fold increase in 5-year mortality risk
Rosinha A et al. DNA repair system and renal cell carcinoma prognosis: under the influence of NBS1. Med Oncol, 2015 (HR 3.92, 95% CI 1.33-11.57).

Notably, breast cancer meta-analyses have consistently shown no significant association¹²¹² no significant association
Yao F et al. Association between the NBS1 Glu185Gln polymorphism and breast cancer risk: a meta-analysis. Tumor Biol, 2013 (14 studies, 6,642 cases, 7,138 controls; OR 1.05, 95% CI 0.80-1.39).

Practical Implications

The E185Q variant produces a small but real reduction in DSB repair capacity. The effect sizes are modest (OR 1.06-1.21 depending on cancer type), consistent with a common variant contributing a small increment of risk. The practical response is to minimize unnecessary DNA damage and support the repair machinery you have.

Zinc is structurally essential for multiple DNA repair proteins, including zinc finger motifs in the MRN complex and downstream repair factors. NAD+ is the substrate consumed by PARP enzymes during the initial DNA damage response -- PARP1 detects strand breaks and uses NAD+ to synthesize poly(ADP-ribose) chains that recruit repair factors including the MRN complex. Maintaining adequate NAD+ levels ensures this signaling pathway operates at full capacity.

Minimizing avoidable sources of DNA damage -- particularly ionizing radiation exposure beyond clinical necessity -- is especially relevant given the documented gene-radiation interaction.

Interactions

NBN works in the same DNA damage response as XRCC1 R399Q (rs25487), ERCC2 D312N (rs1799793), and XRCC1 R194W (rs1799782). XRCC1 coordinates base excision repair and single-strand break repair, while ERCC2 participates in nucleotide excision repair. Individuals carrying risk alleles in both NBN and one or more XRCC genes would have compounded impairment across multiple arms of the DNA damage response. Published studies have examined combined genotype effects on cancer risk, with some finding multiplicative interactions for lung and bladder cancer. A compound action covering NBN E185Q plus XRCC1 risk genotypes could recommend intensified DNA repair support (zinc, NAD+ precursors, and targeted screening) beyond what either individual variant warrants alone.