Abstract
[Purpose]To study the trans-generational effects of atomic-bomb radiation, that is effects on human germline cells, at the genome-wide level, a bacterial artificial chromosome (BAC) DNA micro-array based comparative genomic hybridization (BAC-aCGH) have been introduced. We report the results obtained from 305 individuals by this method. [Experiment] We used an array with about 2,500 BAC-clones distributed across human autosomes. We examined 265 offspring who had at least one parent exposed to high-radiation doses(1.0 Gray or more) and 40 offspring from unexposed parents. [Results] We found 1,534 copy number variants (CNVs) in the genome;of these, 97 CNVs were termed 'rare' CNVs whose frequencies were less than 1%. With respect to rare CNVs, DNA from the offspring and their parents were examined by quantitative polymerase chain reaction to confirm whether or not those CNVs were from their parents. Three rare CNVs identified in three offspring were not identified in either parent and these are defined as 'putative de novo mutants.' One mutant was a deletion type and remaining two were amplification types. We determined the parental origin of the de novo mutants using single nucleotide polymorphisms within the mutated region in the offspring. The results demonstrated that all three de novo mutants occurring on the gametes originated from exposed fathers. [Discussion] This number of de novo mutants (three) is too small to reach a firm conclusion as to whether the mutation rate of the exposed group is significantly higher than that in those from unexposed group. Moreover, in the past data, the mutations caused by radiation seem to favor being deletions. However, in the classic animal studies, duplications could not be detected due to a technical limitation. It will be an important task to test whether segmental duplications occur as commonly as deletions. Therefore, we will continue the study using the high-density array system to 1) increase the number of loci examined in order to increase the number of de novo mutants to be identified, and 2) to get information whether or not duplication-type de novo mutations are radiation-dose related.
