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Bloom Syndrome

Disease characteristics
Bloom syndrome is caused by mutations in the BLM gene (locus 15q26.1), which provides the codes to produce a DNA helicase protein. This protein is essential in correct DNA duplication in cell division process. When a cell prepares to divide to form two cells, the chromosomes are duplicated so that each new cell will get a complete set of chromosomes; this 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.

Prevalence
The carrier frequency in individuals of Eastern European Jewish ancestry is about 1/100. If both parents are carriers, there is a one in four, or 25%, chance with each pregnancy for an affected child.

Mutation
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.

Testing criteria and symptoms

Being of Ashkenazi Jewish ancestry
Small body size
Redness of face aggravated by sun exposure (erythema or butterfly rash).

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