Radiation-induced germline mutations detected by a direct comparison of parents and first-generation offspring DNA sequences containing SNPs.

Germline mutation induction has been detected in mice but not in humans. To estimate the genetic risk of germline mutation induction in humans, new techniques for extrapolating from animal data to humans or directly detecting radiation-induced mutations in man are expected to be developed. We have developed a new method to detect germline mutations by directly comparing the DNA sequences of parents and first-generation offspring. C3H male mice were irradiated with gamma-rays of 3, 2 and 1 Gy and 3 weeks later were mated with C57BL female mice of the same age. The nucleotide sequences of 160 UniSTS markers containing 300-900 bp and SNPs of the DNA of parent and offspring mice were determined by direct sequencing. At each dose of radiation, a total of 5 Mb DNA sequences were examined for radiation-induced mutations. We found 7 deletions in 3 Gy-irradiated mice, 1 deletion in 2 Gy-irradiated mice, 1 deletion in 1 Gy-irradiated mice and no mutations in control mice. The maximum mutation frequency was 2.0 x 10(-4)/locus/Gy at 3 Gy, and these results suggested that a non-linear increase of mutations with dose.