BLM

The BLM gene provides instructions for producing a protein that is a member of the RecQ DNA helicase family. DNA helicases are enzymes that unwind the two spiral strands of a DNA molecule. This activity is necessary before DNA can be copied (replicated) in preparation for cell division. During replication, each chromosome makes two identical DNA structures, called sister chromatids.

The BLM helicase is believed to play a role in recognizing and preventing errors in DNA copying. This protein probably helps to maintain the structure and integrity of a person's DNA.

Bloom syndrome - caused by mutations in the BLM gene

Mutations in the BLM gene result in changes in the helicase enzyme that affect the process of unwinding and copying DNA during replication. Normally, during the copying process, sister chromatids exchange small sections of DNA (sister chromatid exchange). The altered DNA helicase activity, however, causes errors in the copying process. As a result, the frequency of sister chromatid exchange increases about 10-fold. Increased sister chromatid exchange is an indicator of chromosome instability, which probably contributes to the increased risk of cancer and other features of Bloom syndrome.

More than 60 mutations in the BLM gene cause Bloom syndrome. One particular mutation causes almost all cases of Bloom syndrome among people of Central and Eastern European (Ashkenazi) Jewish descent. This mutation involves the deletion of six DNA building blocks (nucleotides) and their replacement by seven others at position 2281 (written as 2281 delta 6ins7, or blmAsh).