Discrimination between complete and incomplete chromosome exchanges in X-irradiated human lymphocytes using FISH with pan-centromeric and chromosome specific DNA probes in combination with telomeric PNA probe

Purpose: To discriminate precisely between radiation-induced complete and i ncomplete chromosome exchanges using chromosome painting together with the detection of the centromeres and telomeres in one FISH assay. Materials and methods: Human lymphocytes were exposed in vitro to X-rays at a dose of 4 Gy. Chromosome aberrations were analysed using the FISH techni que in combination with a whole chromosome-specific DNA probe for chromosom e 8, human pan-centromeric DNA and telomeric PNA probes. Results: The combined FISH assay has improved the resolution of detecting c hromosomal exchanges in human lymphocytes. Results indicate that the freque ncy of observed incomplete exchange patterns was 21% when telomeric signals were ignored during the analysis. When the telomeric signals were included in the analysis a large proportion of apparently incomplete exchange patte rns appeared complete and should be re-classified. The percentage of true i ncomplete exchanges was Found to be less than 5%. Conclusion: The combination of chromosome painting and the detection of cen tromeres and telomeres enable unequivocal discrimination between incomplete and complete exchanges. The fraction of true incomplete exchanges observed in X-irradiated human lymphocytes was found to be low in comparison with p revious reports in the literature.