Bloom syndrome

Lore & Background

Bloom syndrome was first described in 1954 by New York dermatologist Dr. David Bloom. The most prominent feature is proportional small size, apparent in utero, with neonates typically below the third percentile in length, head circumference, and birth weight. A facial rash, erythematous and telangiectatic, develops early in life due to sun exposure, most prominently on the cheeks, nose, and around the lips, and can also affect the backs of the hands and neck. The rash is variably expressed and less severe in females on average, and sun sensitivity may resolve in adulthood.

Reader's Guide

Bloom syndrome is significant as a model for understanding genomic instability and cancer predisposition. The disorder is caused by mutations in the BLM gene, which encodes a RecQ DNA helicase involved in DNA replication and repair. Cells from affected individuals exhibit a striking genomic instability, including a roughly 10-fold increase in sister chromatid exchange and elevated homologous recombination. This instability leads to a high risk of cancer, with over half of individuals in the Bloom Syndrome Registry diagnosed with malignancies, often at an earlier age than in the general population and with multiple primary cancers. The syndrome also features immune deficiency, endocrine disturbances, and reduced fertility. Bloom syndrome shares features with Fanconi anemia and is related to Bloom-syndrome-like disorder caused by mutations in other components of the same protein complex.

Did You Know?

• Bloom syndrome is caused by mutations in the BLM gene, a member of the RecQ DNA helicase family.
• Cells from persons with Bloom syndrome exhibit a sister chromatid exchange rate approximately 10-fold higher than normal.
• The facial rash in Bloom syndrome is erythematous and telangiectatic, and is less severe in females on average.
• The average life span for individuals with Bloom syndrome is approximately 27 years, with cancer being the most common cause of death.