SEX IS AN IMPORTANT VARIABLE AFFECTING SPONTANEOUS MICRONUCLEUS FREQUENCY IN CYTOKINESIS-BLOCKED LYMPHOCYTES

The micronucleus frequency in cytokinesis-blocked lymphocytes of 152 f emales and 113 males aged between 20 and 89 years (minimum of 15 subje cts per sex per decade) was compared. Marked differences in the micron ucleus frequency of males and females were observed: (a) there was a g reater dispersion in the results for females when compared to males in all age groups older than 40 years; (b) there was a significant posit ive correlation between micronucleus frequency and age in both sexes ( p < 0.0001) but the slope of the linear regression line was steeper in females (slope = 0.499 micronuclei/year) compared to males (slope = 0 .289 micronuclei/year) (p < 0.0045); (c) the micronucleus frequency in females (M(f)) was significantly higher than the micronucleus frequen cy in males (M(m)) in all decades examined (p < 0.05), the M(f),M(m) r atio varied between 1.47 and 1.65 (mean +/- 1 SEM = 1.53 +/- 0.03) and showed no trend with age. These results suggest that an added mechani sm, possibly the loss of X chromosomes, is contributing to the micronu cleus frequency in females and highlights the importance of sex as a v ariable that has to be taken into consideration when interpreting data from cross-sectional studies utilising the cytokinesis-block micronuc leus assay as a biomarker of chromosome damage.