Micronuclei and Chromosome Aberrations Found 1n Bone Marrow Cells and Lymphocytes from Thorotrast Patients and Atomic Bomb Survivors

As two cytogenetic parameters of radiation exposure, the frequency of micronucleus in erythroblasts, lymphocytes and red cells (Howell-Jolly body) as well as chromosome aberrations in bone marrow cells and in lymphocytes were studied in 24 thorotrast patients and in 32 atomic bomb (A-bomb) survivors who were exposed within one kilometer from the Hiroshima hypocenter. The incidence of both micronucleus and chromosome aberrations in these two exposed groups were significantly higher than that in non-exposed controls. So that these two parameters are useful guide for evaluating the residual effects of radiation, especially on hematopoietic cells. Because of its simple procedures, micronucleus test is also helpful as screening for prediction of chromosome aberrations. The characteristics of lymphocyte chromosome aberrations differed considerably between thorotrast patients and A-bomb survivors; the incidence of unstable type aberrations and intracellular complexity of chromosome aberrations were much higher in the former group. The incidence of micronucleus in erythroblasts and lymphocytes was also higher in thorotrast patients. Such differences are attributable to the differences in the radiation quality (α-ray or γ-ray + neutron) and in the mode of exposure (persistent or single) of these two groups.