Background ionizing radiation plays a minor role in the production of chromosome translocations in a control population

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Abstract
Purpose: To obtain a relationship between background chromosome translocation frequency and age with translocation frequency measured to a high statistical precision, and to identify the role of background ionizing radiation in the production of chromosome translocations in a control population. Materials and methods: Lymphocytes from 35 healthy control individuals (15 females and 20 males) were scored, using fluorescence in situ hybridization, for the presence of chromosomal translocations. Translocation frequencies were measured to a high statistical precision (s.d. 25% or less for each individual). These control subjects were of varying ages, ranging from 0 (cord blood) to 98 years. Results: In a total of 521,492 metaphases (203,754 genome equivalent cells) scored, an average of 5,822 genome equivalent cells per individual, 764 translocations were observed in the 35 individuals. The translocation frequencies ranged from 0 (for cord blood) to 0.0167 (for a 98 year old) translocations per cell. The average age and translocation frequency was 50 years and 0.004 translocations per cell, respectively. The best fit of the relationship between translocations and age was: Y = 7 x 10-4 + 6.9 x 10-6 A + 1.35 x 10-6 A2, which does not obey the linear relationship expected from chronic background radiation alone. The curvilinear relationship observed clearly shows that other endogenous and exogenous clastogens or clastogenic events, in addition to radiation, serve to generate chromosome translocations in control populations. Conclusion: The background translocation frequency in control individuals follows a curvilinear relationship with age. No significant variation was observed between individuals of the same age. Clastogenic processes of normal aging and physiological factors in additional to ionizing radiation play a major role in the production of chromosome translocations in a control population. Background radiation, however, appears to play a minor role in chromosome translocation production in control individuals living near sea level.