35 a 25).71 No two-hit aberrations were found in the f unexposed group, but both groups had an unusual numberof acentric fragments, the cause of which is not known. Paradoxically, Rongelap people & om wf a X, X@ ? ig ¢ ~ a e 4¢* v S: “~~ é gr % 04 Sf ~ ty ~ oie eae ow > Ss =a fishermen,?? on victims of other radiation acci- dents,’ and on Japanese bomb survivors.74 2. Somatic Mutations In 1974, studies* were made of the frequency of amino acid substitution in the hemoglobin of the Marshallese on blood samples sent to Oak Ridge.”5 Since there is no coded isoleucine’6 in adult human hemoglobin A, its presence must be due to f=: wo poe. than those with the higher exposure. These studies indicate that a small but significant number of chromosomeaberrations persisted in blood lymphocytes in some Marshallese as late as 10 years after exposure. The results are consistent with those of similar studies on the exposed Japanese errors in transcription or translation or to somatic mutationsarising during DNAreplication. Errors in transcription, which occur infrequently, form a. t with the lower exposure had more aberrations e Figure 25. Two-hit chromosomeaberrations in exposed Marshallese. Top: arrow points to dicentric form; bottom: arrow points to ring form. !2 altered mRNA, tRNA, and rRNA; they change the coding in the mRNA and may reduce fidelity of the tRNA with regard to beth thé i’ of aminoacid it accepts and the mRNA éodonsit recognizes.77 Errors in translation”? arise through the attachment of wrong amino acids totRNA (aminoacyl synthetase errors) and the imprecise recognition of mRNAcodons by tRNAanticodons (translational variation). Somatic mutationsresult from mistakes in replication of DNA; manysingle- base-substitution mutations change nonisoleucine into isoleucine codons,’8 and the resulting mutant cells could have hemoglobin mRNAwithisoleu- cine codons. For this reason, an increase in theiso- leucine content of hemoglobin A would be expected in humans exposed to agents causing basesubstitution mutations. Possibly radiation may cause base-substitution mutations in humansomatic cells, but this has never been established. >20) and 8 unexposed Rongelap people.* Chromosomeaberrations were noted in 23 of the exposed andin 5 of the unexposed Marshallese, but the exposed group had a numberof two-break aberrations (represented by dicentric chromosomes, translocations, and a ring form) that are thought to be associated with radiation exposure (Figure *These analyses were done by Drs. H. Lisco, New England Deaconess Hospital, and R.A. Conard, BNL. Theisoleucine content of the hemoglobin A was determined in biood from 13 exposed Marshallese and 12 unexposed. Thefrequency of isoleucine substitution for other aminoacids in hemoglobin was calculated by dividing the nanomolesofisoleucine by the total nanomoles ofall other amino acids in each sample. The frequenciesare listed in Table 21. *These studies were done by Drs. R.A. Popp, G.P. Hirsch, and E.G. Bailiff at Oak Ridge National Laboratory.