Complex chromatid-isochromatid exchanges following irradiation with heavy ions?

We describe a peculiar and relatively rare type of chromosomal rearrangement induced in human peripheral lymphocytes that were ostensibly irradiated in G₀ phase of the cell cycle by accelerated heavy ions, and which, to the best of our knowledge, have not been previously described. The novel rearrangements which were detected using mFISH following exposure to 500 MeV/nucleon and 5 GeV/n ⁵⁶Fe particles, but were not induced by either ¹³⁷Cs gamma rays or ²³⁸Pu alpha particles, can alternatively be described as either complex chromatid-isochromatid or complex chromatid-chromosome exchanges. Different mechanisms potentially responsible for their formation are discussed.