 Loss of only a single Ku80 allele in Ku(-/+) heterozygous mice causes accelerated aging in skeletal muscle, although post natal growth is normal.An analysis of the level of Ku80 protein in human, cow, and mouse indicated that Ku80 levels vary dramatically between species, and that these levels are strongly correlated with species longevity.These results suggest that the NHEJ pathway of DNA repair mediated by Ku80 plays a significant role in repairing double-strand breaks that would otherwise cause early senescence (see DNA damage theory of aging).