Mutations in the genes that encode Nbs1 and Mre11, which are part of the RMN complex, are responsible for the human radiation sensitivity disorder, the Nijmegen breakage syndrome (NBS), and the ataxia-telangiectasia-like disorder (ATLD), which are characterized by defective checkpoint responses and high levels of chromosomal abnormalities [94]. Here, MRE11 is linked to Nijmegen breakage syndrome.