Bloom Syndrome

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What is Bloom syndrome?

Bloom syndrome is an inherited disorder characterized by a high frequency of breaks and rearrangements in an affected person's chromosomes. 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.

Other features of the disorder may include learning disabilities, mental retardation, chronic lung problems, diabetes, and immune deficiency that leads to recurrent pneumonia and ear infections. Men with Bloom syndrome usually do not produce sperm, and as a result are unable to father children (infertile). Women with the disorder generally experience menopause earlier than usual.

Chromosome instability in Bloom syndrome results in a high risk of cancer in affected individuals. Affected individuals develop the full range of cancers found in the general population, but the cancers arise unusually early in life. People with Bloom syndrome may be first diagnosed with cancer at about 25 years old.

How common is Bloom syndrome?

Bloom syndrome is a very rare disorder in most populations, and its overall frequency is unknown. It is more common in people of Central and Eastern European (Ashkenazi) Jewish background, among whom 1 in 48,000 are affected. Approximately one third of people with Bloom syndrome are of Ashkenazi Jewish descent.

What genes are related to Bloom syndrome?

Mutations in the BLM gene cause Bloom syndrome.

The BLM gene provides instructions for producing a protein called the Bloom (BLM) syndrome protein, which is a member of the DNA helicase family. DNA helicases are enzymes that unwind the two spiral strands of a DNA molecule so that they can be copied.

When a cell prepares to divide to form two cells, the chromosomes are duplicated (replicated) so that each new cell will get a complete set of chromosomes. The replication process involves unwinding the DNA so that it can be copied. The BLM protein is important in maintaining the stability of the DNA during this process. Mutations in the BLM gene alter or reduce the BLM protein's DNA helicase activity, which causes errors in the copying process during replication. As a result, people with Bloom syndrome have a higher frequency of chromosome breakage and rearrangement than unaffected people. This increase in chromosome breakage and rearrangement leads to the signs and symptoms of Bloom syndrome.

How do people inherit Bloom syndrome?

This condition is inherited in an autosomal recessive pattern, which means two copies of the gene in each cell are altered. Most often, the parents of an individual with an autosomal recessive disorder each carry one copy of the altered gene but do not show signs and symptoms of the disorder.

Source: National Institutes of Health

Reports summarize Bloom syndrome genetics research from Columbia University, Department of Microbiology

"To explore the role of BLM in the immune system, we ablated murine Blm in the T-cell lineage. In the absence of Blm, thymocytes were severely reduced in numbers and displayed a developmental block at the beta-selection checkpoint that was partially p53 dependent. Blm-deficient thymocytes rearranged their T-cell receptor (TCR) beta genes normally yet failed to survive and proliferate in response to pre-TCR signaling. Furthermore, peripheral T cells were reduced in numbers, manifested defective homeostatic and TCR-induced proliferation, and produced extensive chromosomal damage. Finally, CD4(+) and CD8(+) T-cell responses were impaired upon antigen challenge," wrote H. Babbe and colleagues, Columbia University, Department of Microbiology.

The researchers concluded: "Thus, by ensuring genomic stability, Blm serves a vital role for development, maintenance, and function of T lymphocytes, suggesting a basis for the immune deficiency in Bloom's syndrome."

Babbe and colleagues published their study in Molecular and Cellular Biology (The Bloom's syndrome helicase is critical for development and function of the alphabeta T-cell lineage. Molecular and Cellular Biology, 2007;27(5):1947-59).

For more information, contact H. Babbe, Columbia University Medical Center, Dept. of Microbiology, 701 W 168th St., New York City, NY 10032 USA.

Publisher contact information for the journal Molecular and Cellular Biology is: American Society Microbiology, 1752 N St. NW, Washington, DC 20036-2904, USA.

Keywords: United States, New York, Bloom Syndrome Genetics, Bloom Syndrome, Cellular, Genetics.

This article was prepared by Life Science Weekly editors from staff and other reports. Copyright 2007, Life Science Weekly via NewsRx.com.