Functional Polymorphisms in Oxidant Metabolism and DNA Repair Pathways and Risk of Leukemia and Transient Myeloproliferative Disorder in Children with Down Syndrome

Children with Down syndrome can have a wide range of developmental abnormalities related to the presence of additional genetic material from a small region of chromosome 21. Additional copies of the Cu/Zn superoxide dismutase gene and related genes at this locus are believed to contribute to high oxidative stress, and increased endogenous DNA damage and deficient repair observed in cells from patients with Down syndrome. Children with Down syndrome also have a markedly increased risk for the development of serious hematological disorders, including an approximately 20-fold increased risk for the development of acute myeloid leukemia (AML). In addition, in early infancy, as many as 10% may develop a transient myeloproliferative disorder (TMD). The basis for this overall increased risk is unknown, as are the risk factors influencing which specific patients with Down syndrome develop AML/TMD. We sought to test the hypothesis that functional polymorphisms in genes involved in oxidant metabolism and DNA repair contribute to the increased risk of AML and TMD in children with Down syndrome. We studied functional polymorphisms in the oxidant metabolizing enzyme NADPH quinone oxidoreductase 1 (NQO1), and in the DNA repair proteins X-ray repair cross complementing 1 protein (XRCC1) and Fanconi anemia complementation group A protein (FANCA). Genotyping was conducted in 170 patients with Down syndrome AML or TMD, and 202 healthy blood donor controls. All genotype frequencies in the control populations were consistent with those expected from Hardy-Weinberg equilibrium. We found that the variant NQO1 Pro187Ser allele, associated with reduced quinone reductase activity, occurred with a greater frequency in the Down syndrome AML/TMD patient population compared to healthy controls (OR, 1.61; 95% CI, 1.067-2.426; p=0.0231). The FANCA-1501 variant allele frequency was observed more frequently in Down syndrome AML/TMD patients compared to healthy controls (OR, 1.77; 95%CI, 1.220-2.568; p=0.0025). The variant XRCC-1 Arg399Gln allele was observed less frequently in the TMD/DS AML population as compared to controls (OR, 0.536; CI, 0.354-0.811; p=0.0031). These latter findings parallel the observation of a protective effect against AML in non-Down syndrome individuals with at least one copy of the XRCC-1 Arg399Gln allele (Seedhouse et al. Blood 2002, 100:3761). Conclusion: These preliminary studies, representing the only reported data in Down Syndrome TMD/AML patients, suggest that functional polymorphic variants of the NQO1, FANCA, and XRCC1 genes involved in oxidant metabolism and DNA repair may influence the risk for developing leukemia. Studies involving future cohorts will be needed to confirm these observations.