Bloom syndrome is a rare chromosomal breakage syndrome characterized by a marked genetic instability associated with pre- and postnatal growth retardation, facial sun-sensitive telangiectatic erythema, increased susceptibility to infections, and predisposition to cancer. Other usual features are poor feeding during infancy, and an exceptionally sparse subcutaneous adipose tissue giving a wasted appearance. Dolichocephaly, narrow face, prominent nose and ears, and malar and mandibular hypoplasia can be observed.
Bloom syndrome is due to mutations of the BLM gene (15q26.1) which encodes the DNA helicase RecQl3, an enzyme involved in maintenance of genomic integrity. Such mutations lead to a spontaneous high level of sister chromatid exchanges due to a slowdown in replication speed and defective fork reactivation.
