Human disease has been described due to mutations in MRE11 (Ataxia-Telangiectasia-like disorder, OMIM #604391) [4–6], RAD50 (Nijmegen Breakage Syndrome-like disorder) [7•,8] and NBN, and although the somatic phenotype shows some common features, significant immunodeficiencies are confined to patients with NBN mutations giving rise to Nijmegen Breakage syndrome (NBS) (OMIM #251260). This evidence concerns the gene RAD50 and Nijmegen breakage syndrome.