Long-term persistence of translocations in stable lymphocytes from victims of a radiological accident

Purpose: To investigate whether translocations in ʹstableʹ lymphocytes, i.e. those not containing unstable aberrations in any chromosome including counterstained ones, would have a longer persistence with time compared with those measured in all cells. Materials and methods: The time-course of chromosomal aberrations in the three most highly exposed radiation victims of an Estonian accident in November 1994 was followed for 7 post-accident years encompassing 15 samples. Chromosome painting was performed using probes for chromosomes 1, 2 and 4 with a pan-centromeric probe, and chromosomal aberrations involving the painted chromosomes were scored using a developed version of the Protocol for Aberration Identification and Nomenclature Terminology (PAINT) nomenclature. Metaphases containing aberrations were captured with an image analyser and stored on a computer. An earlier analysis of aberrations in the painted portion of the genome was performed in all cells, irrespective of the possible aberrations in the unpainted part of the genome. The present analysis has taken into account the ʹstable/unstableʹ nature of the complete cell. Evaluation was performed on images, counting all chromosomes and checking the counterstained chromosomes for unstable aberrations, i.e. dicentrics, acentrics or ring chromosomes. Results: In the original analyses of all cells, a decrease in translocation frequency in the early samples was observed. In the present study of stable cells, the results showed that the yield of translocations is constant with time. Conclusions: The results show that translocations observed in stable cells are persistent with time. This implies that retrospective dosimetry and calibration should be performed using stable cells. To obtain more information on this issue, the stability status of all cells in any future fluorescence in situ hybridization follow-up of a radiation accident should be noted.