A A Awa

This paper presents an analysis of the utility of fluorescence in situ hybridization (FISH) with whole-chromosome probes for measurement of the genomic frequency of translocations found in the peripheral blood of individuals exposed to ionizing radiation. First, we derive the equation: Fp = 2.05fp(1-fp)FG, relating the translocation frequency, Fp, measured using FISH to the genomic translocation frequency, FG, where fp is the fraction of the genome covered by the composite probe. We demonstrate the validity of this equation by showing that: (a) translocation detection efficiency predicted by the equation is consistent with experimental data as fp is changed; (b) translocation frequency dose-response curves measured in vitro using FISH agree well with dicentric frequency dose-response curves measured in vitro using conventional cytogenetic procedures; and (c) the genomic translocation frequencies estimated from FISH measurements for 20 Hiroshima A-bomb survivors and four workers exposed to ionizing radiation during the Y-12 criticality accident are approximately the same as the translocation frequencies measured using G-banding. We also show that translocation frequency dose response curves estimated using FISH are similar for Hiroshima A-bomb survivors and for first division lymphocytes irradiated in vitro. We conclude with a discussion of the potential utility of translocation frequency analysis for assessment of the level of acute radiation exposure independent of the time between analysis and exposure.

The advent of chromosome painting has brought the realization that structural aberrations can be far more complicated than previously imagined. Various investigators have devised their own nomenclature systems to deal with this difficulty, with the result that the terminology has become inconsistent and confusing. Recently, an international group of cytogeneticists experienced in chromosome painting gathered to address this issue. Results of the meeting are presented in this report, which provides a nomenclature system capable of describing chromosome aberrations that occur between painted and unpainted chromosomes, as well as aberrations involving only painted chromosomes. The nomenclature is flexible enough to describe accurately even the extensively rearranged chromosomes. As a consequence of this flexibility, the scheme upon which the nomenclature is based differs substantially from other systems of aberration classification. We call this system the Protocol for Aberration Identification and Nomenclature Terminology (PAINT).

The data collected in Hiroshima and Nagasaki during the past 40 years on the children of survivors of the atomic bombings and on the children of a suitable control population are analyzed on the basis of the newly revised estimates of radiation doses. No statistically significant effects emerge with respect to eight different indicators. Since, however, it may confidently be assumed some mutations were induced, we have taken the data at face value and calculated the minimal gametic doubling doses of acute radiation for the individual indicators at various probability levels. An effort has also been made to calculate the most probable doubling dose for the indicators combined. The latter value is between 1.7 and 2.2 Sv. It is suggested the appropriate figure for chronic radiation would be between 3.4 and 4.5 Sv. These estimates suggest humans are less sensitive to the genetic effects of radiation than has been assumed on the basis of past extrapolations from experiments with mice.

Radiation-induced chromosome aberrations were found to persist in cultured peripheral blood lymphocytes derived from Hiroshima and Nagasaki A-bomb survivors long after their radiation exposure. Earlier observations that the frequency of cells with chromosome aberrations increased in proportion with increasing dose in both cities were confirmed. However, in every dose group, the frequency of aberrant cells was consistently higher in Hiroshima than in Nagasaki. It is suggested that a higher neutron dose in Hiroshima than in Nagasaki may be a major component contributing to the difference in dose response between the two cities. Among the types of chromosome aberrations so far identified, reciprocal translocations were observed to predominate, and they played an important role in determining the dose-aberration relationship.