Risk of childhood leukemia associated with diagnostic irradiation and polymorphisms in DNA repair genes

The purpose of the study was to measure risk of childhood acute lymphoblastic leukemia associated with reported postnatal diagnostic X rays and to determine if it was modified in the presence of variants in genes involved in DNA repair. We conducted a population-based case-control study with 491 cases and 491 healthy controls among children 0-9 years of age at diagnosis. To evaluate gene-environment interaction, we used a subgroup of 129 cases. The adjusted odds ratio (OR) for one reported postnatal child X ray versus none was 1.04 [95% confidence interval (CI), 0.72-1.49], whereas the OR for two or more X rays was 1.61 (CI, 1.13-2.28). Among girls, the former ORs were 1.14 (CI, 0.66-1.96) and 2.26 (1.20-4.23), respectively. Among girls who carried the hMSH3 [exon (ex) 23] variant, the ORs were 3.33 (CI, 0.75-14.82) for one X ray and 0.27 (CI, 0.05-1.57) for two or more X rays, whereas among those who carried the XRCCI (ex 6) variant, the ORs were 1.45 (0.11-19.08) and 6.66 (0.78-56.63), respectively. On the other hand, at low levels of exposure, boys seemed protected by the variant hMLH1 (ex 8). The latter results must be interpreted with caution bur suggest that the effect of diagnostic X rays could be modified by variants in repair genes according to sex. Few studies have evaluated the risk of postnatal diagnostic irradiation, which was moderately strong here; we are not aware of any studies that also considered the effect of polymorphisms in DNA repair genes. Based on the present results, both aspects deserve further study.