Interestingly, mutations in MRN component genes Meiotic Recombination 11 (Mre11) or Nijmegen Breakage Syndrome 1 (NBS1), which are linked to A-T-like disorder and Nijmegen breakage syndrome, respectively, are accompanied by defective ATM activity with symptoms resembling those of A-T patients [16,17], suggesting that MRN is required for the activation of ATM in vivo. Here, ATM is linked to Nijmegen breakage syndrome.