Abstract
Aberrant class switch recombination (CSR), the physiological process that regulates maturation of the antibody response, is believed to be an early event in the pathogenesis of myeloma. The genetic basis of CSR, from initiation of the DNA double-strand break through to detection and repair, has been elucidated. We hypothesised that germline polymorphisms in the genes implicated in DNA double strand break repair may contribute to susceptibility to myeloma. We therefore assessed 32 SNPs in 3 genes central to the DNA repair pathway in patients with myeloma and controls from the EpiLymph Study, a European study of the epidemiology of lymphoid neoplasms, and from an Irish hospital registry (306 cases, 263 controls). The genes examined were XRCC3, XRCC4, and XRCC5. XRCC3 is a member of the RecA/Rad51-related protein family that participates in homologous recombination. The XRCC4 protein forms a complex with DNA ligase IV and DNA-dependent protein kinase in the repair of DNA double-strand breaks by non-homologous end joining. XRCC5 encodes the 80-kilodalton subunit of the Ku heterodimer protein, the DNA-binding component of the DNA-dependent protein kinase. SNPs from the chosen genes were identified from HapMap CEU Phase I and II genotype data (Public Release #20; 2006-01-24). Haplotype-tagging SNPs (htSNPs) were chosen based on Tagger analysis (as implemented in Haploview Version 3.2). A SNP in GSTP1 was also genotyped to allow for comparison with allele frequencies previously generated from a myeloma cohort. Genotyping was performed using TaqMan®-based assays on the 7900 ABI HT platform. The drop-out rate was consistently less than 3% in all assays. For quality control (QC) purposes, duplicates of 10% of the samples were interspersed throughout the plates. The concordance rates for QC samples were greater than 98%. GSTP1 SNP results were comparable to previously published findings. For the htSNP rs963248 in XRCC4, Allele A was significantly more frequent in cases than in controls (86.4% vs.80.8%) (p=0.0105), as was the AA genotype (74% vs. 65%) (p=0.026). Haplotype analysis was performed using Cocaphase for rs963248 in combination with additional SNPs in XRCC4. The strongest evidence of association came from the A - T haplotype from rs963248-rs2891980 (80.9% vs. 74.5%; p=0.008). For XRCC5, the genotype GG from rs1051685 was detected in 10 cases from different national populations but in only 1 control (p=0.015). Interestingly, this SNP is located in the 3′ UTR of XRCC5. Overall, these data provide support for the hypothesis that common variation in the genes encoding DNA repair proteins contributes to susceptibility to myeloma.
The catalytic subunit of DNA-dependent protein kinase is required for cellular resistance to oxidative stress independent of DNA double-strand break repair
