NBN and Nijmegen breakage syndrome: Mutations in the NBS1 encoding gene, NBN, are associated with Nijmegen breakage syndrome (NBS) (OMIM# 251260) characterized by microcephaly, immunodeficiency, growth and intellectual disability, radiosensitivity, and cancer predisposition.1, –, 3 Mutations in RAD50 gene RAD50 are related to NBS-like disorder (NBSLD) (OMIM# 613078).4 The clinical features of patients with NBSLD are very similar to those with NBN, including microcephaly and intellectual disability but not infections, immunodeficiency, or cancer predisposition.