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MOLECULAR STUDIES OF MUTATION SUGGEST THAT THE EARTH’S SPACE ENVIRONMENT IS NOT MUTAGENIC.  B.W. Glickman, M. Khaidakov, and A. Mortimer^b.  Centre for Environmental Health, University of Victoria, Victoria BC; ^bSpace Science Program, Canadian Space Agency, Ottawa.

Somatic mutation levels were measured and the nature of mutations characterised in five Russian cosmonauts with recent long-term spaceflight experience and four age-matched trainees using the clonal HPRT assay.  Hprt mutant frequencies in both cosmonaut and trainee groups were very similar, 17.2 ± 0.6 and 17.6 ± 4.7 x 10^-6, respectively. However, these values are about twice that of the age-corrected values established for healthy, unexposed subjects in Western countries (Tates et al., 1991; Branda et al., 1993), low lower than the HPRT mutant frequencies observed in cosmonaut samples in our previous study (Khaidakov et al., 1997). A total of 124 mutant clones were sequenced and the mutational spectra in the cosmonauts and trainees were essentially similar. However, they were significantly different from the Western mutational spectrum (p=0.031 and 0.038), and exhibited a higher incidence of splice errors and complex mutations. These data suggest that the space environment is not genotoxic at the HPRT locus. Interestingly, the uniformly high hprt mutant frequencies observed in the Moscovite samples (Khaidakov et al., 1997; Curry et al., 1997; Jones et al., 1995) indicate a higher mutagenic burden in Russia, possibly reflecting a combination of environmental and dietary factors.