Significant associations between X-ray repair cross-complementing group 3 genetic polymorphisms and thyroid cancer risk

Polymorphisms of DNA Repair Genes in Thyroid Cancer

The incidence of thyroid cancer, one of the most common forms of endocrine cancer, is increasing rapidly worldwide in developed and developing countries. Various risk factors can increase susceptibility to thyroid cancer, but particular emphasis is put on the role of DNA repair genes, which have a significant impact on genome stability. Polymorphisms of these genes can increase the risk of developing thyroid cancer by affecting their function. In this article, we present a concise review on the most common polymorphisms of selected DNA repair genes that may influence the risk of thyroid cancer. We point out significant differences in the frequency of these polymorphisms between various populations and their potential relationship with susceptibility to the disease. A more complete understanding of these differences may lead to the development of effective prevention strategies and targeted therapies for thyroid cancer. Simultaneously, there is a need for further research on the role of polymorphisms of previously uninvestigated DNA repair genes in the context of thyroid cancer, which may contribute to filling the knowledge gaps on this subject.

Thyroid Cancer: The Quest for Genetic Susceptibility Involving DNA Repair Genes

The incidence of thyroid cancer (TC), particularly well-differentiated forms (DTC), has been rising and remains the highest among endocrine malignancies. Although ionizing radiation (IR) is well established on DTC aetiology, other environmental and genetic factors may also be involved. DNA repair single nucleotide polymorphisms (SNPs) could be among the former, helping in explaining the high incidence. To further clarify the role of DNA repair SNPs in DTC susceptibility, we analyzed 36 SNPs in 27 DNA repair genes in a population of 106 DTCs and corresponding controls with the aim of interpreting joint data from previously studied isolated SNPs in DNA repair genes. Significant associations with DTC susceptibility were observed for XRCC3 rs861539, XPC rs2228001, CCNH rs2230641, MSH6 rs1042821 and ERCC5 rs2227869 and for a haplotype block on chromosome 5q. From 595 SNP-SNP combinations tested and 114 showing relevance, 15 significant SNP combinations (p < 0.01) were detected on paired SNP analysis, most of which involving CCNH rs2230641 and mismatch repair variants. Overall, a gene-dosage effect between the number of risk genotypes and DTC predisposition was observed. In spite of the volume of data presented, new studies are sought to provide an interpretability of the role of SNPs in DNA repair genes and their combinations in DTC susceptibility.

Correlation between polymorphisms of BRAF gene and papillary thyroid carcinoma

BACKGROUND

Papillary thyroid carcinoma (PTC), which accounts for 80% of all thyroid cancers, has an increasing incidence over these years. Single nucleotide polymorphisms (SNPs) of BRAF were considered to be one of well-established risk factors leading to development of PTC. The aim of this study was to investigate whether the common mutations of BRAF could elevate significantly the risk of PTC in a Chinese population.

METHODS

Four SNPs (rs11762469, rs17623204, rs1267636 and rs3748093) of BRAF were selected through our filter by Haploview 4.2 software with HapMap databases. We used the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) to genotype the four SNPs in blood samples of 618 subjects (206 patients with PTC and 412 healthy controls). The correlation between BRAF polymorphisms and PTC risk was assessed using student t-test and chi-square test.

RESULTS

The results showed that mutation in rs3748093 was significantly associated with an increased risk of PTC in allele model (A allele vs. T allele, OR = 1·68, 95% CI = 1·16-2·43, P = 0·006), dominant model (TA + AA vs TT, OR = 1·64, 95% CI = 1·08-2·48, P = 0·019) and homozygote model (AA vs. TT, OR = 2·94, 95% CI = 1·00-8·61, P = 0·040). However, the other three SNPs (rs11762469, rs17623204 and rs1267636) were shown to have no association with the risk of PTC.

CONCLUSIONS

Our results indicated that polymorphism of rs3748093*A was significantly correlated with an increased risk of PTC in a Chinese population. Further investigation on the aetiological mechanism of PTC is needed to validate our results.

Association Between X-Ray Cross-complementing Group 3 (XRCC3) Thr241Met Polymorphism and Risk of Thyroid Cancer: A Meta-Analysis

Background

The X-ray cross-complementing group 3 (XRCC3) gene encodes a protein that plays an important role in homologous recombination repair (HRR) of DNA double-strand break (DSB). Increasing attention has been drawn to the association of XRCC3 T241M polymorphism with various types of human cancers. In this study, a meta-analysis was performed to investigate whether there is an association between XRCC3 T241M polymorphism and thyroid cancer risk.

Material/Methods

A comprehensive search was conducted and a total of 8 studies that covered 963 thyroid cancer cases and 1942 controls were included in this analysis. The meta-analysis was performed on both overall database and 2 ethnic subgroups (Caucasian and Asian). The fixed-effects model was used to calculate odds ratio (OR) with 95% confidence intervals (CIs). The publication bias was evaluated using Begg’s funnel plots and Egger’s test.

Results

A positive association between XRCC3 T241M polymorphism and thyroid cancer risk was found by the analyses of the overall database using both recessive model (OR=1.40, 95% CI=1.08–1.81, P=0.012) and homozygote comparison (OR=1.41, 95% CI=1.07–1.86, P=0.015), but not by that using the dominant model (OR=1.12, 95% CI=0.95–1.33, P=0.18). However, no significant association of XRCC3 Thr241Met polymorphism with the risk of thyroid cancer was found in individual ethnic subgroups.

Conclusions

We conclude that the XRCC3 Thr241Met polymorphism is associated with an increased risk of thyroid cancer in the overall population, while no significant association was observed in individual ethnic subgroups due to limited population size.

The significance of Exo1 K589E polymorphism on cancer susceptibility: evidence based on a meta-analysis

The exonuclease1 (Exo1) gene is a key component of mismatch repair (MMR) by resecting the damaged strand, which is the only exonuclease involved in the human MMR system. The gene product is a member of the RAD2 nuclease family and functions in DNA replication, repair and recombination. However, whether Exo1 is required to activate MMR-dependent DNA damage response (DDR) remains unknown, the conclusions of the Exo1 polymorphisms on cancer susceptibility studies were not consistent. We carried out a meta-analysis of 7 case-control studies to clarify the association between the Exo1 K589E polymorphism and cancer risk. Overall,a significant association of the Exo1 K589E polymorphism with cancer risk in all genetic models (Lys vs Glu: OR = 1.51, 95%CI:1.39-1.99, P<0.01; Glu/Lys vs Glu/Glu: OR = 1.43, 95%CI:1.28-1.60, P<0.01; Lys/Lys vs Glu/Glu: OR = 2.45, 95%CI:1.90-3.17, P<0.01; Lys/Lys+Glu/Lys vs Glu/Glu: OR = 1.53, 95%CI:1.38-1.71, P<0.01; Glu/Glu vs Glu/Lys+Lys/Lys: OR =  2.27, 95%CI:1.79-2.89, P<0.01). In the stratified analysis by ethnicity, significantly increased risk was observed in Asian population (Lys vs Glu: OR = 1.53, 95%CI:1.39-1.69, P<0.01; Glu/Lys vs Glu/Glu: OR = 1.50, 95%CI:1.34-1.69, P<0.01; Lys/Lys vs Glu/Glu: OR = 2.48, 95%CI:1.84-3.34, P<0.01; Lys/Lys+Glu/Lys vs Glu/Glu: OR = 1.58, 95%CI:1.41-1.78, P<0.01; Glu/Glu vs Glu/Lys+Lys/Lys: OR = 2.18, 95%CI:1.62-2.93, P<0.01). Subgroup analysis based on smoking suggested Exo1 K589E polymorphism conferred significant risk among smokers (Lys/Lys+Glu/Lys vs Glu/Glu: OR = 2.16, 95%CI:1.77-2.63, P<0.01), but not in non-smokers (Lys/Lys+Glu/Lys vs Glu/Glu: OR = 0.89, 95%CI:0.64-1.24, P = 0.50). In conclusion, Exo1 K589E Lys allele may be used as a novel biomarker for cancer susceptibility, particularly in smokers.