Augmented cell death with Bloom syndrome helicase deficiency

Bloom syndrome (BS) is a rare autosomal genetic disorder characterized by lupus-like erythematous telangiectasias of the face, sun sensitivity, infertility, stunted growth, upper respiratory infection, and gastrointestinal infections commonly associated with decreased immunoglobulin levels. The syndrome is associated with immunodeficiency of a generalized type, ranging from mild and essentially asymptomatic to severe. Chromosomal abnormalities are hallmarks of the disorder, and high frequencies of sister chromatid exchanges and quadriradial configurations in lymphocytes and fibroblasts are diagnostic features. BS is caused by mutations in BLM, a member of the RecQ helicase family. We determined whether BLM deficiency has any effects on cell growth and death in BLM-deficient cells and mice. BLM-deficient EB-virus-transformed cell lines from BS patients and embryonic fibroblasts from BLM^-/- mice showed slower growth than wild-type cells. BLM-deficient cells showed abnormal p53 protein expression after irradiation. In BLM^-/- mice, small body size, reduced number of fetal liver cells and increased cell death were observed. BLM deficiency causes the up-regulation of p53, double-strand break and apoptosis, which are likely observed in irradiated control cells. Slow cell growth and increased cell death may be one of the causes of the small body size associated with BS patients.