Bloom's syndrome (BS) is a rare human autosomal recessive disorder belonging to a group of 'chromosomal breakage syndromes''. BS is characterized by marked genetic instability, including a high level of sister chromatid exchanges, associated with a greatly increased predisposition to a wide range of cancers commonly affecting the general population. The constant clinical features of BS are proportionate pre- and postnatal growth retardation and cancer predisposition. Additional clinical features include dolichocephaly, facial sun-sensitive telangiectatic erythema, patchy areas of hyper- and hypopigmentation of the skin and moderate to severe immunodeficiency manifested by recurrent respiratory tract and gastrointestinal infections. A 10-fold increase in the rate of sister chromatid exchanges (SCEs) in BS cells compared to normal cells is the only objective criteria for BS diagnosis. Clinical diagnosis is confirmed cytogenetically by demonstrating characteristic chromosome instability. BS arises through mutations in both copies of the BLM gene which encodes a 3'-5' DNA helicase, a member of the RecQ family. The function of the BLM protein remains unclear, but several lines of evidence support a major role in maintaining genomic stability during DNA replication, recombination and repair. BS frequency in the general population is unknown, probably because this disease is very rare. In Askenazic Jewish population, the frequency of BS is approximately 1 in 48 000. This is due to a founder effect, approximately 1% of the Ashkenasi Jewish population being heterozygous carriers for the blmAsh mutation. There is no curative treatment for BS. However, a physician should carefully follow BS patients in order to ensure early diagnosis of cancer.
Last update: February 2004