Bloom syndrome: A rare inherited condition characterized by photosensitivity, raised, red skin blotches, growth deficiency and increased susceptibility to infectious diseases and tumors. Bloom syndrome: Bloom syndrome is an autosomal recessive disorder associated with mutations in BLM gene encoding protein that belongs to the family of DNA helicases. It is characterized by predisposition to cancer, immunodeficiency, high sensitivity to UV and genomic instability of somatic cells.
People with Bloom syndrome are much smaller than average, and often have a high-pitched voice and characteristic facial features including a long, narrow face; small lower jaw; and prominent nose and ears. They tend to develop pigmentation changes and dilated blood vessels in the skin, particularly in response to sun exposure. These changes often appear as a butterfly-shaped patch of reddened skin on the face. The skin changes may also affect the hands and arms.
Bloom syndrome is diagnosed by clinical features and can be confirmed by chromosome analysis. A greatly increased frequency of sister chromatid exchanges (SCEs) in cells exposed to bromodeoxyuridine (BUDR) is diagnostic; Bloom syndrome is the only disorder in which such evidence of hyper-recombination is known to occur. BLM is the only gene known to be mutated in Bloom syndrome. Molecular genetic testing for the common mutation, BLMAsh, is clinically available.