Increased somatic cell mutant frequency in atomic bomb survivors.

Frequencies of mutant T-cells in peripheral blood, which are deficient in hypoxanthine guanine phosphoribosyltransferase (HPRT) activity, were determined for atomic bomb survivors by direct clonal assay using a previously reported method (Hakoda et al., 1987). Results from 30 exposed survivors (more than 1 rad exposed) and 17 age- and sex-matched controls (less than 1 rad exposed) were analyzed. The mean mutant frequency (Mf) in the exposed (5.2 X 10(-6); range 0.8-14.4 X 10(-6)) was significantly higher than in controls (3.4 X 10(-6); range 1.3-9.3 X 10(-6)), which was not attributable to a difference in non-mutant cell-cloning efficiencies between the 2 groups, which were virtually identical. An initial analysis of the data did not reveal a significant correlation between individual Mfs and individual radiation dose estimates when the latter were defined by the original, tentative estimates (T65D), even though there was a significant positive correlation of Mfs with individual frequency of lymphocytes bearing chromosome aberrations. However, reanalysis using the newer revised individual dose estimates (DS86) for 27 exposed survivors and 17 controls did reveal a significant but shallow positive correlation between T-cell Mf values and individual exposure doses. These results indicate that HPRT mutation in vivo in human T-cells could be detected in these survivors 40 years after the presumed mutational event.