The majority of NBS patients originates from Eastern Europe and is homozygous for a common founder mutation in the NBN gene, namely a deletion of nucleotide positions 657 to 661 of the coding sequence in exon 6 (abbreviated as c.657del5; rs587776650) that leads to two truncated fragments, p26- and p70 nibrin [9]. Here, NBN is linked to Nijmegen breakage syndrome.