Relationship between genetic polymorphisms of DNA ligase 1 and non-small cell lung cancer susceptibility and radiosensitivity

Evaluation of the influence of chronic low-dose radiation on DNA repair gene polymorphisms [XRCC1, XRCC3, PRKDC (XRCC7), LIG1, NEIL1] in individuals from normal and high level natural radiation areas of Kerala Coast

Background: Single Nucleotide Polymorphisms (SNPs) at DNA repair genes are considered as potential biomarkers of radio-sensitivity. The coastal belt of Kerala in south west India has a patchy distribution of monazite in its beach sand that contains Th-232 and its decay products. Thus, radiation levels in this area vary from <1.0mGy to 45.0mGy/year. The areas with external gamma radiation dose >1.5mGy/year are considered as High-Level Natural Radiation Areas (HLNRA) and ≤ 1.5mGy/year are Normal Level Natural Radiation Area (NLNRA).Objective: In the present study, an attempt was made to evaluate the influence of chronic low dose radiation exposure on DNA repair gene polymorphisms in NLNRA and HLNRA population of Kerala coast.Materials and methods: Genomic DNA was isolated from venous blood samples of 246 random, healthy individuals (NLNRA, N = 104; HLNRA, N = 142) and genotyping of five SNPs such as X-ray repair cross complementing 1(XRCC1 Arg399Gln), X-ray repair cross complementing 3 (XRCC3 Thr241Met], Protein kinase, DNA-activated, catalytic subunit (PRKDC) (X-ray repair cross-complementing group 7, XRCC7 G/T), nei like DNA glycosylase 1 (NEIL1 G/T) and DNA ligase 1 (LIG1 A/C) was carried out using PCR based restriction fragment length polymorphism (PCR-RFLP) followed by silver staining.Results: Our results showed no significant difference in genotype frequencies in HLNRA vs NLNRA at three of the five SNPs studied i.e. XRCC1 Arg399Gln (χ²₍₂₎ = 5.85, p = .054), XRCC3 Thr241Met (χ²₍₁₎ = 0.71, p = .339), PRKDC (XRCC7 G/T) (χ²₍₂₎ = 3.72, p = .156), whereas significant difference was observed at NEIL1 G/T (χ²₍₂₎ =8.71, p = .013) and LIG1 A/C (χ²₍₂₎ = 7.66, p = .022). The odds of heterozygote to homozygote genotypes in HLNRA relative to NLNRA at XRCC1 Arg399Gln (OR = 1.96, 95% CI: 1.13-3.40), XRCC3 Thr241Met (OR = 0.73, 95% CI: 0.41-1.31), PRKDC (XRCC7 G/T), (OR = 0.81; 95% CI: 0.48-1.38), NEIL1 G/T (OR = 0.54; 95% CI: 0.31-0.96) and LIG1 A/C (OR = 1.62; 95% CI: 0.97-2.69) was also not significantly different in HLNRA vs NLNRA, except at XRCC1 and NEIL1.Conclusion: The genotype frequencies at three of these SNPs i.e. XRCC1 Arg399Gln, XRCC3 Thr241Met and PRKDC (XRCC7 G/T) were similar, whereas NEIL1 G/T and LIG1 A/C showed significant difference between HLNRA and NLNRA population. However, further research using more number of SNPs in a larger cohort is required in this study area.

Germline Variants in DNA Repair Genes, Diagnostic Radiation, and Risk of Thyroid Cancer

Background: Radiation exposure is a well-documented risk factor for thyroid cancer; diagnostic imaging represents an increasing source of exposure. Germline variations in DNA repair genes could increase risk of developing thyroid cancer following diagnostic radiation exposure. No studies have directly tested for interaction between germline mutations and radiation exposure.Methods: Using data and DNA samples from a Connecticut population-based case-control study performed in 2010 to 2011, we genotyped 440 cases of incident thyroid cancer and 465 population-based controls for 296 SNPs in 52 DNA repair genes. We used multivariate unconditional logistic regression models to estimate associations between each SNP and thyroid cancer risk, as well as to directly estimate the genotype-environment interaction between each SNP and ionizing radiation.Results: Three SNPs were associated with increased risk of thyroid cancer and with thyroid microcarcinoma: HUS rs2708896, HUS rs10951937, and MGMT rs12769288. No SNPs were associated with increased risk of larger tumor (>10 mm) in the additive model. The gene-environment interaction analysis yielded 24 SNPs with P_interaction < 0.05 for all thyroid cancer, 12 SNPs with P_interaction < 0.05 for thyroid microcarcinoma, and 5 SNPs with P_interaction < 0.05 for larger tumors.Conclusions: Germline variants in DNA repair genes are associated with thyroid cancer risk and are differentially associated with thyroid microcarcinoma and large tumor size. Our study provides the first evidence that germline genetic variations modify the association between diagnostic radiation and thyroid cancer risk.Impact: Thyroid microcarcinoma may represent a distinct subset of thyroid cancer. The effect of diagnostic radiation on thyroid cancer risk varies by germline polymorphism. Cancer Epidemiol Biomarkers Prev; 27(3); 285-94. ©2017 AACR.