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Radiation-Induced Mutations in Mammals

1950; Radiological Society of North America; Volume: 55; Issue: 4 Linguagem: Inglês

10.1148/55.4.579

1527-1315

Donald R. Charles,

Radioactive contamination and transfer

There are two particular questions about radiation-induced mutations in mammals which should be of interest to radiologists: (1) How likely are mutations to occur, as a function of dose? (2) How serious are their effects? Let us first remind ourselves of the main classes of mutations recognized by geneticists. Figure 1 shows a hypothetical pedigree involving a dominant gene mutation; Figure 2 represents a recessive gene mutation, and Figure 3 an inherited semi-sterility caused by a chromosome translocation. How frequently such changes occur in mammals as a result of exposure to radiation is still far from accurately known. The published data, all obtained from mice (Table I) indicate that, for single large exposures, inherited semi-sterilities are the main genetic effect to be expected, occurring in a small percentage of sperm for each 100 r. The gene mutation rates are not very reliable, since they are calculated from a few mutations in a small number of tested cells (Table II). For practical applications, one would like to know something about mutation rates under repeated small exposures to penetrating radiation. Such data were obtained at the University of Rochester Atomic Energy Project between 1943 and the present. They are summarized in Table III. These results may be compared with those of the previous investigators for single doses (Table IV). Both the disagreements in chromosome mutation rate and the agreement in dominant gene mutation rate are to be expected from the results of many workers with plants and insects. In those organisms, the gene changes depend only on total dose, no matter how spaced in time; the chromosome changes depend very strongly on dosage rate. Hence we may take the lower (University of Rochester) value as more nearly applicable to human tolerance problems. Let us now turn to the question: How serious are the effects of radiation-induced mutations? Our basis for judgment—so far as gene mutations are concerned—is very scanty. The types of change may be listed as follows: 1. Retarded growth (Hertwig) 2. Anemia, early death (Hertwig) 3. Oligodactyly, early death (Hertwig) 4. Abnormal spleen shape (Snell) 5. Abnormal connections of minor tributaries of vena cava (Charles) 6. Extra nodules of adrenal cortical tissue (Charles) 7. Incomplete suture of parietal bones (Charles) 8. "Confused" behavior, occasional cataract and deafness (Charles) 9. Reduced eye size and fertility, altered fur color (Charles) 10. Altered fur color (Charles). Of the twelve mutations, perhaps only 7 show clearly adverse effects, but it is the general impression of geneticists, I believe, that most mutant genes, when adequately studied, are found to be harmful. We know somewhat more about the semi-sterility mutations.