Their importance, however, is highlighted by the observation that interference with ATM and Chk2 function severely impairs the checkpoint response to IR and other DSB-inducing lesions, and mutation of the genes encoding for ATM and Chk2 results in the cancer-prone Ataxia-Telangiectasia syndrome, and familial breast and prostate cancer, respectively [81]–[87]. This evidence concerns the gene ATM and Ataxia-telangiectasia.