Persistence of translocations in stable cells

The time-course of chromosomal aberrations in three radiation victims of the 1994 Estonian accident was followed for a period of seven post accident years encompassing 15 samples. Chromosome painting was performed and chromosomal aberrations involving the painted chromosomes were scored using a developed version of the PAINT nomenclature. Metaphases containing aberrations were captured with an image analyser and stored in computer. Originally, data 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 accounts for the “stable/unstable” nature of the complete cell. This evaluation was performed on images, counting all chromosomes and checking the counterstained chromosomes for unstable aberrations, ie. dicentrics, acentrics or ring chromosomes. With this approach we investigated whether translocations in “stable” cells, that is those not containing unstable aberrations in any chromosome including counterstained ones, would have a better persistence with time. During the production of new lymphatic cells, this type of cell would have a better potential to survive during cell division than those containing so called unstable aberrations. In earlier analyses of all cells, a decrease in the early samples was observed in the highly exposed individuals. In the present study of stable cells, the results showed that the yield of translocations is independent of time. Similar results have been found in a follow-up study of stable cells after an accident in Turkey. In three samples taken 1, 9 and 21 months after the accident, the yield of translocations was unchanged in four victims whereas there was a clear decrease of yield in all cells. These findings imply that translocations are persistent and that retrospective dosimetry and calibration should be performed in stable cells.