MRE11 and Nijmegen breakage syndrome: In addition, mutations in DNA damage signalling kinase ATM have been linked to Ataxia-telangiectasia, whereas Ataxia-telangiectasia-like disorder (ATLD) and Nijmegen breakage syndrome (NBS) are caused by mutations in two components of the MRN complex, MRE11 and NBS1 respectively.