Nijmegen chromosomal instability syndrome (NBS , OMIM 251260 ) is a rare entity. The disease seems to be typical for the region of Central and Eastern Europe. Only in Poland recorded 81 of the approximately 140 cases described in the world. Basic clinical symptoms include microcephaly , growth disorders , immunodeficiency . The team is accompanied by an increased predisposition to the development of malignant tumors at a young age . Nijmegen syndrome is inherited in an autosomal recessive manner . NBS for the development team responsible germinal mutations of the NBS1 gene . The most common mutation is a deletion 5PZ ( 657del5 ) in exon 6 of the NBS1 gene . This mutation called Slavic occurs in 90% of patients with NBS . NBS1 gene mutations affect the disturbance in the functioning of its protein product - nibryny being a part of the complex repair of DNA DSBs MRE11/RAD50/Nibryna (M / R / N). Therefore patients with NBS cells exhibit spontaneous chromosomal instability and cell cycle abnormalities resulting from sensitivity to ionizing radiation and radiomimetics .