A Polymorphism Study on Detoxification and DNA Repair Genes in 700 MDS Patients Demonstrates An Association Between Genotype and An Aberrant Karyotype

The maintenance of genetic stability within haematopoietic stem cells is essential for normal haematopoiesis and this is emphasised by the association of leukemias and myelodysplastic syndromes (MDS) with genetic instability. DNA is normally protected from damage via a number of complex pathways including detoxification and DNA repair pathways. Inefficient processing of DNA damage may result in an increased susceptibility to leukemia and MDS. Genetic polymorphisms exist in many genes within the DNA damage processing pathways, some of which affect the cells ability to maintain genetic stability. We have studied polymorphisms in the homologous DNA repair genes RAD51 (RAD51-g135c) and XRCC3 (XRCC3-Thr241Met) and the detoxification gene GSTM1 (deletion polymorphism) in more 700 MDS samples. The GSTM1 polymorphism was studied using PCR, and the RAD51 and XRCC3 genotypes were assayed simultaneously using a SNaPshot technique. The genotype distributions of RAD51-g135c and GSTM1 did not differ significantly from those reported in the literature. However the distribution of the XRCC3-Thr241Met polymorphism was found to be significantly different, with an over-representation of the variant Met allele, when compared to previously published frequencies in control populations¹ (odds ratio (OR) 1.8; 95% confidence interval (CI) 1.3–2.6, p<0.001). Whilst the presence of a single polymorphic variant may display only a subtle effect, polymorphic variants of more than one gene involved in the same pathway are likely to be biologically important with respect to the cellular ability to maintain genetic integrity and hence may play a role in MDS pathogenesis. RAD51, XRCC3 and GSTM1 genotypes were therefore studied in combined analyses. Similar to studies in AML¹, the double DNA repair gene variant (RAD51–135c/XRCC3–241) was over-represented in MDS compared to a control population (OR 3.8; 95% CI 1.6–9.3, p=0.002). The triple variant genotype (RAD51–135c/XRCC3–241Met/GSTM1-null) was associated with a further increased risk of MDS (OR 13.5; 95% CI 1.8–102.8, p=0.01). More detailed analysis was undertaken to compare the polymorphic distributions in MDS with aberrant karyotypes. When the single genes were assessed, the GSTM1 null genotype was the only one to be over-represented in MDS with an aberrant karyotype compared to MDS with a normal karyotype (OR 1.6; 95% CI 1.05–2.5). Interestingly, when analysing the genotypes with respect to the XRCC3/RAD51 combined genotypes the presence of homozygous wild type alleles of one DNA repair gene matched with the presence of a variant allele of the other DNA repair gene is significantly protective against karyotypic abnormalities when compared to the double WT patients (OR 0.29; 95% CI 0.29–0.78; p=0.003). Collectively these results suggest that polymorphisms in genes which process DNA damage play a significant role in MDS pathogenesis and may also contribute to genetic instability in MDS.