Chicago Center for Jewish Genetics Disorders - Ashkenazi Disorders: Bloom Syndrome

Ashkenazi Disorders: Mendelian

Gene: The gene that causes Bloom Syndrome is DNA helicase, RecQ-like, type 2 gene (BLM gene; OMIM 604610), which is located at 15q26.1. It has not yet been established how mutations in this gene cause the symptoms seen in Bloom Syndrome, but it is believed that the absence of the BLM gene product probably destabilizes other enzymes that participate in DNA replication and repair. This could occur either through direct interaction with these enzymes or through more general responses to DNA damage.

Mutations and testing: A single mutation called blmAsh mutation (2881 delta 6ins7) is responsible for ~97% of mutant alleles seen in Ashkenazi Jews. No other mutation is tested for.

Traits: Characteristics commonly seen in Bloom syndrome are small stature (average adult male height of 151 cm, average adult female height of 144 cm), skin photosensitivity, and a high-pitched voice. A typical facial appearance has also been described consisting of a narrow face with prominent nose and prominent ears. Immunodeficiency has been seen, which results in an increased number of respiratory tract and ear infections. Adult-onset diabetes is also seen in Bloom syndrome in ~10% of cases. There can be decreased fertility, mental retardation, and learning disabilities also. The hallmark of Bloom syndrome is chromosomal instability, which is seen as an increased rate of chromosomal breakage and sister chromatid exchange. This leads to a predisposition for development of multiple cancers. Heterozygotes do not have increased rates of sister chromatic exchanges or cancer.

Treatment: Treatment is mainly preventative with increased surveillance for cancer and decreased exposure to sunlight and X-rays. Bone marrow transplant is a possibility.

Reviewed by Dr. Joel Charrow, Children's Memorial Hospital.
1/03

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This page last updated on January 10, 2003.