NBN and Nijmegen breakage syndrome: In humans, homozygous hypomorphic mutations in MRE11, NBN (coding for the NBS1 protein) and RAD50 genes cause ataxia telangiectasia‐like disorder (ATLD‐OMIM:604391), Nijmegen breakage syndrome (NBS‐OMIM:251260) and NBS‐like disorder (NBSLD‐OMIM:613078), respectively.