AGE-RELATED INCREASE OF BASE-LINE FREQUENCIES OF SISTER-CHROMATID EXCHANGES, CHROMOSOME-ABERRATIONS, AND MICRONUCLEI IN HUMAN-LYMPHOCYTES

Intra- and interindividual variations of baseline frequencies of cytog enetic end points in lymphocytes of human populations have been report ed by various authors. Personal characteristics seem to account for a significant proportion of this variability. Several studies investigat ing the role of age as a confounding factor in cytogenetic biomonitori ng found an age-related increase of micronucleus (MN) frequency, where as contradictory results were reported for chromosomal aberrations (CA s) and sister chromatid exchanges (SCEs). We have quantitatively evalu ated the effect of age on SCE, CA, and MN through the analysis of a po pulation sample that included data from several biomonitoring studies performed over the last few decades in 12 Italian laboratories. The la rge size of the data set, i.e., more than 2000 tests for each end poin t, allowed us to estimate the independent effect of age, taking into a ccount other covariates, such as sex, smoking habits, occupational exp osure, and inter- and intralaboratory variability A greater frequency of the mean standardized values by increasing of age was observed for all of the end points. A leveling off was evident in the last age clas ses in the trend of MN frequencies. Frequency ratios (FRs), which expr ess the increase of the cytogenetic damage with respect to the first a ge classes, i.e., 1-19 years, were estimated using Poisson regression analysis after adjustment for the potential confounding factors and co nfirmed the increasing trend by age class for all three end points. Th e most dramatic increase was observed for MN, with a FR that approache s the value of 2 at the age class 50-59 (FR, 1.97; 95% confidence inte rval, 1.43-2.71) and remains substantially unchanged thereafter. The t rend of FRs for CA is more homogeneous,,vith a constant rise even in t he older classes, whereas the frequency of SCE increases with age to a lesser extent, reaching a plateau in the age class 40-49 and the maxi mum value of FR in the age class over 70 (FR, 1.14; 95% confidence int erval, 1.07-1.23). In conclusion, our results point to an age-related increase of the chromosome damage in lymphocytes and emphasize the nee d to take into account the potential confounding effect of this variab le in the design of biomonitoring studies based on chromosome damage.