Nijmegen breakage syndrome

Nijmegen breakage syndrome, abbreviated NBS, is a rare autosomal recessive congenital disorder that causes chromosomal instability, probably because of a defect in the double Holliday junction DNA repair mechanism or the synthesis dependent strand annealing mechanism that repairs double strand breaks in DNA. The NBS1 gene codes for a protein called nibrin, which stops the cell cycle in the S phase when the cell DNA contains errors and interacts with FANCD2, which can activate the BRCA1 and BRCA2 repair pathway. Mutations in NBS1 therefore lead to higher levels of cancer. The name comes from the Dutch city of Nijmegen, where the condition was first described. Most people with the syndrome have West Slavic origins, and the largest number live in Poland.