Comments on the Paper by Wickliffe et al. (Radiat. Res. 159, 458–464, 2003)

Wickliffe et al. (1) recently published data on mitochondrial DNA (mtDNA) heteroplasmy in laboratory mice exposed to a very low-dose-rate chronic irradiation in the vicinity of the Chernobyl nuclear power plant. Given that the issue of mutation induction by very low-dose-rate irradiation remains controversial (2), it may appear that the results of this publication could provide new insights with regard to the validity of the extrapolation of genetic risk from data on high/medium-dose-rate irradiation. Indeed, according to the authors, the main result of this study suggests that very low-dose-rate chronic irradiation with a cumulative dose of 1.5 Gy does not affect the mutation rate in somatic tissues and that therefore the current linear, no-threshold model of radiation risk (3) should be re-evaluated. It should be stressed, however, that mutation induction at mtDNA in the irradiated animals has never been proven experimentally, which raises...