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International study of translocations in control populations


Congress title :BiodosEPR-2006 2nd International Conference on Biodosimetry and 7th International Symposium on ESR Dosimetry and Applications
Congress location :Bethesda
Congress date :10/07/2006

Summary

  Biological monitoring of radiation dose can contribute important, independent estimates of exposure for individuals and populations, especially when physical measurements of radiation exposure are unavailable. Translocations have been the most widely applied biological marker of past radiation exposure in epidemiologic studies, because of well-characterized radiation dose-response curves and the persistence of translocations that can be detected many years later. Establishing baseline levels of translocations will contribute to the usefulness of this technique in cases of accidental radiation exposure.
It is well accepted that the frequency of chromosome aberrations increases with radiation exposure and age, but the effect of gender, ethnicity and lifestyle factors (such as cigarette smoking) on background translocation yields is not known with certainty. Pooled analyses of translocation data in unexposed individuals have been conducted, but the largest study to date included only 385 persons. Background aberration frequencies were overwhelmingly influenced by age, but the effect of age as modified by gender and cigarette smoking remains unclear. We sought to expand the number of contributing laboratories with the goal of establishing control levels of translocation frequencies by age, gender, ethnicity and smoking status.
Fifteen laboratories in North America, Europe and Asia contributed translocation frequency data on 1,957 unexposed individuals, with a minimum of 200 cell equivalents (CE) per individual. Ages ranged from newborn (cord blood) to 85 years. The study population was 37% female, 40% reported ever smoking, and 77% were Caucasian, 13% Black, 8% Asian, and 2% were other ethnicity. Age was the strongest predictor of translocation frequency (p<0.001). The mean number of translocations was 0.03/100 CE (95% confidence interval=0.02-0.04) for newborns and 1.7/100 CE (95%CI 1.4-2.0) for subjects 75 years and older. An analysis of the effects of gender showed that translocation frequencies per 100 CEs were similar for men and women up to about age 50, when they diverged, with women having higher frequencies than men. Smokers had higher translocation frequencies than non-smokers (p < 0.001) after adjustment for gender, ethnicity, and laboratory. We noted significant variation by laboratory in all analyses. We were unable to separate the effect of ethnicity on translocations from inter-laboratory variation. More work is needed to understand the different types of age responses in different populations.

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