ESTIMATE OF TRUE INCOMPLETE EXCHANGES USING FLUORESCENCE IN-SITU HYBRIDIZATION WITH TELOMERE PROBES

Purpose: To study the frequency of true incomplete exchanges in radiat ion-induced chromosome aberrations. Materials and methods: Human lymph ocytes were exposed to 2 Gy and 5 Gy of gamma-rays. Chromosome aberrat ions were studied using the fluorescence in situ hybridization (FISH) technique with whole chromosome-specific probes, together with human t elomere probes. Chromosomes 2 and 4 were chosen in the present study. Results: The percentage of incomplete exchanges was 27% when telomere signals were not considered. After excluding false incomplete exchange s identified by the telomere signals, the percentage of incomplete exc hanges decreased to 11%. Since telomere signals appear on about 82% of the telomeres, the percentage of true incomplete exchanges should be even lower and was estimated to be 3%. This percentage was similar for chromosomes 2 and 4 and for doses of both 2 Gy and 5 Gy. Conclusions: The percentage of true incomplete exchanges is significantly lower in gamma-irradiated human lymphocytes than the frequencies reported in t he literature.