RADIATION-INDUCED CHROMOSOME ABERRATIONS IN MAN.

Abstract

A study has been undertaken of the production and elimination of radiation-induced chromosome aberrations in luekocytes taken from the peripheral blood of persons exposed to chronic or acute doses of high-energy radiation (1). Among the chronically exposed groups are radiologists and scientists working in university or industrial laboratories for whom there are available complete records of the radiation dose received during their working lifetime. We have also included a group of “distinguished radiologists,” men who have been practicing radiology for over twenty-five years, who may have received substantial doses of radiation early in their careers. Figure 1 shows seven karyotypes—a karyotype is a systematized array of chromosomes of a single cell—observed in leukocytes obtained from a distinguished radiologist. The twenty-two pairs of autosomes are arranged in two rows in decreasing order of size. The X, Y chromosome pair is arranged at the extreme right of each set. As can be seen, six of the seven cells are unexceptionable, but in the chromosome set at the top of the figure one chromosome is missing from the largest pair of autosomes and an extra chromo-some is present in the medium-sized group. We classify a cell containing such a set of chromosomes as “pseudo-diploid,” since the forty-six apparently normal chromosomes cannot be arranged in matching pairs. The detection of pseudo-diploid cells is a rather tedious business. It is much easier to scan a large number of cells for the presence of "remarkable interchanges," aberrant figures formed by the radiation cross-linking of two or more chromosomes. The largest group in this class consists of the dicentrics, several of which are shown in Figure 2. The four karyotypes displayed in this figure are of leukocytes taken from a patient twenty-five days after he received a total-body dose of 300 r. The impression they give is one of chaos. Only the presence of forty-six centromeres in each karyotype remains to recall the rigid order of the normal diploid karyotype. Table II gives additional results obtained on patients who received 300 rads of total-body irradiation. The first patient showed some evidence of recovery ten days after treatment; this may be due to an injection of autologous bone marrow immediately after irradiation. The second patient, who is the source of Figure 2, showed no real evidence of recovery twenty-five days after irradiation. The data are too meager, however, to permit any meaningful calculation of the rate of elimination of radiation-induced chromosome aberrations, with or without bone marrow injections, in people receiving large total-body doses. Table I gives the results obtained with a control group and two groups exposed to chronic irradiation. The control group is listed as receiving 0 rem.