Microsatellite instability in B-cell lymphoma originating from Bloom syndrome

Bloom syndrome (BS) is a rare autosomal recessive genetic disorder characterized by lupus-like erythematous telangiectasias of the face, sun sensitivity, stunted growth infertility and immunodeficiency. In addition, BS patients are highly predisposed to cancers. Although recently the causative gene of BS (BLM) was identified as a DNA helicase homologue, the function of BLM in DNA replication has not been elucidated. In this study, p53 mutation and microsatellite instability in B-cell lymphomas originating from 2 sibling BS patients were investigated. In the originally developed tumor of both patients, no p53 mutation was detected. In one patient, however, after treatment by ionizing radiation the B-cell lymphoma recurred, showing a 9-bp deletion in exon 7. In lymphoma cells and an EB-virus-transformed cell line from BS lymphocytes of this patient, microsatellite instability was also detected from the reduced length of microsatellite DNA markers, although in the other patient microsatellite instability was not detected. Thus, 2 B-cell lymphomas, despite having the same BLM mutation, showed different phenotypes in terms of p53 mutation and microsatellite instability.