Bloom syndrome

The BLM gene provides the instructions for making a protein in the RecQ helicase family called BLM. Helicases are proteins that bind to DNA and help to unwind the two strands of the DNA molecule. Unwinding the strands of the DNA molecule is necessary to make copies of it in preparation of cell division and repairing damaged DNA.

When cells get ready to divide and form two cells, the DNA that makes up the chromosomes is copied so that each new cell will have two copies of each chromosome. These two copies of the DNA are initially joined and can trade and share pieces of their DNA. The protein made by the BLM gene prevents too many DNA pieces from being shared or traded.

Having mutations in the BLM gene cause an individual to have BLM protein that does not work. Without this protein, the two copies of the DNA will trade 10x more often. Breaks in DNA are much more common in these people and they are less able to repair the damage or breaks in their DNA.

Not all changes in the BLM gene cause Bloom syndrome. At least 17 changes in the gene have been identified that do not cause the condition.