FREQUENCY, DISTRIBUTION AND CLONALITY OF CHROMOSOME-DAMAGE IN HUMAN-LYMPHOCYTES BY MULTICOLOR FISH

Whole chromosome painting was used to determine whether the use of dif ferent sets of paints would influence results obtained from the analys is of human peripheral blood lymphocytes from 27 healthy unexposed sub jects, Painting was also used to determine if aberration frequencies a re proportional to the size of selected chromosomes in human lymphocyt es irradiated in vitro. The in vitro results showed that the frequenci es of radiation-induced stable aberrations (i.e. translocations and in sertions) in chromosomes 3, 5 and 6 painted in unique colors are propo rtional to chromosome size, Aberration frequencies in the normal subje cts were measured using two different sets of paints, one set for chro mosomes 3, 5 and 6 where each chromosome was labeled in a unique color and one set where chromosomes 1, 2 and 4 were painted in a single col or. The frequency of aberrations among chromosomes 1-6 in the populati on as a whole was also found to be proportional to chromosome size. Ho wever, some individual subjects had a distribution of damage that was not proportional to chromosome size due to the presence of clones of a bnormal cells. Aberration frequencies measured in chromosomes 3, 5 and 6 as a set were highly correlated with those observed in chromosomes 1, 2 and 4 as a set, after adjusting for the different amounts of the genome that were painted. We also determined whether differences exist in the aberration frequencies measured by two scoring systems: the cl assical method, where reciprocal exchanges are scored as single events , and PAINT, where each break junction is scored as a single event. Th e two scoring systems gave highly correlated results for translocation s and differed by a constant value (PAINTx0.58 = classical method), Ap proximately 27% of translocations were observed to be nonreciprocal du e to a failure to detect exchanges involving small amounts of material or to a non-reciprocal exchange mechanism. Our results support the hy pothesis that cytogenetic evaluations for biodosimetry can be performe d with any one or more of the chromosomes studied here and indicate th at the aberration frequency measurements are independent of the scorin g system selected for the evaluation. We also present a simple statist ical method for identifying subjects that may possess clonal aberratio ns.