Nijmegen breakage syndrome in a Dutch patient not resulting from a defect in NBS1.

EDITOR—Nijmegen breakage syndrome (NBS) is a rare autosomal recessive chromosomal instability disorder characterised by microcephaly, immunodeficiency, x ray hypersensitivity, and predisposition to malignancy. The gene responsible for NBS, NBS1, is located on chromosome 8q21 and encodes a protein called nibrin. This protein is a component of the hMre11/hRad50 protein complex, suggesting defective DNA double strand break (DSB) repair or cell cycle checkpoint function in NBS. In this report we describe a patient with the NBS phenotype, typical cytogenetic presentation with aberrations in chromosomes 7 and 14, and increased x ray sensitivity. Our index patient had deafness unlike all the other NBS patients reported so far. Mutation detection did not show a mutation in NBS1 and the protein nibrin was normally expressed.