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Genetics Home Reference: your guide to understanding genetic conditions     A service of the U.S. National Library of Medicine®


Reviewed November 2010

What is the official name of the BLM gene?

The official name of this gene is “Bloom syndrome, RecQ helicase-like.”

BLM is the gene's official symbol. The BLM gene is also known by other names, listed below.

What is the normal function of the BLM gene?

The BLM gene provides instructions for making a member of a protein family called RecQ helicases. Helicases are enzymes that bind to DNA and temporarily unwind the two spiral strands (double helix) of the DNA molecule. This unwinding is necessary for copying (replicating) DNA in preparation for cell division and for repairing damaged DNA. Because RecQ helicases maintain the structure and integrity of DNA, they are known as the "caretakers of the genome."

When a cell prepares to divide to form two cells, the DNA that makes up the chromosomes is copied so that each new cell will get a complete set of chromosomes. The copied DNA from each chromosome is arranged into two identical structures, called sister chromatids, which are attached to one another during the early stages of cell division. Sister chromatids exchange small sections of DNA (sister chromatid exchange) during this time.

The BLM protein interacts with several other proteins involved in the maintenance of genome integrity. With the help of its partner proteins, BLM suppresses sister chromatid exchanges and helps to maintain the stability of the DNA during the copying process. Researchers believe BLM restarts the DNA copying process when it stalls, an event that probably happens frequently in the cell. In the absence of BLM activity, DNA copying restarts through a mechanism called homologous recombination that results in sister chromatid exchange.

How are changes in the BLM gene related to health conditions?

Bloom syndrome - caused by mutations in the BLM gene

More than 70 BLM gene mutations have been identified in people with Bloom syndrome. One particular mutation causes almost all cases of Bloom syndrome among people of Central and Eastern European (Ashkenazi) Jewish descent. This mutation deletes six DNA building blocks (nucleotides) and replaces them with seven others at position 2281 (written as 2281 delta 6ins7, or blmAsh). The blmAsh mutation results in the production of an abnormally short, nonfunctional version of the BLM protein. Other BLM gene mutations change single protein building blocks (amino acids) in the protein sequence or create a premature stop signal in the instructions for making the protein.

Mutations in the BLM gene prevent the protein from performing its function in maintaining genome stability. As a result of the altered BLM protein activity, the frequency of sister chromatid exchange increases about 10-fold, which is a hallmark of Bloom syndrome. Increased sister chromatid exchange is an indicator of chromosome instability. It is associated with gaps and breaks in the genetic material that impair normal cell activities and cause the health problems associated with this condition. Cancer results from genetic changes that allow cells to divide in an uncontrolled way. Altered BLM protein activity may also lead to an increase in cell death, resulting in slow growth in affected individuals.

Where is the BLM gene located?

Cytogenetic Location: 15q26.1

Molecular Location on chromosome 15: base pairs 90,717,326 to 90,815,461

The BLM gene is located on the long (q) arm of chromosome 15 at position 26.1.

The BLM gene is located on the long (q) arm of chromosome 15 at position 26.1.

More precisely, the BLM gene is located from base pair 90,717,326 to base pair 90,815,461 on chromosome 15.

See How do geneticists indicate the location of a gene? ( in the Handbook.

Where can I find additional information about BLM?

You and your healthcare professional may find the following resources about BLM helpful.

You may also be interested in these resources, which are designed for genetics professionals and researchers.

What other names do people use for the BLM gene or gene products?

  • Bloom syndrome
  • Bloom syndrome protein
  • BS
  • MGC126616
  • RECQL3

See How are genetic conditions and genes named? ( in the Handbook.

What glossary definitions help with understanding BLM?

acids ; cancer ; cell ; cell division ; chromatid ; chromosome ; DNA ; double helix ; gene ; genome ; helicase ; molecule ; mutation ; protein ; protein sequence ; sister chromatid ; sister chromatid exchange ; syndrome

You may find definitions for these and many other terms in the Genetics Home Reference Glossary (


  • Amor-Guéret M, Dubois-d'Enghien C, Laugé A, Onclercq-Delic R, Barakat A, Chadli E, Bousfiha AA, Benjelloun M, Flori E, Doray B, Laugel V, Lourenço MT, Gonçalves R, Sousa S, Couturier J, Stoppa-Lyonnet D. Three new BLM gene mutations associated with Bloom syndrome. Genet Test. 2008 Jun;12(2):257-61. doi: 10.1089/gte.2007.0119. (
  • Amor-Guéret M. Bloom syndrome, genomic instability and cancer: the SOS-like hypothesis. Cancer Lett. 2006 May 8;236(1):1-12. Epub 2005 Jun 13. Review. (
  • Bugreev DV, Yu X, Egelman EH, Mazin AV. Novel pro- and anti-recombination activities of the Bloom's syndrome helicase. Genes Dev. 2007 Dec 1;21(23):3085-94. Epub 2007 Nov 14. (
  • Cheok CF, Bachrati CZ, Chan KL, Ralf C, Wu L, Hickson ID. Roles of the Bloom's syndrome helicase in the maintenance of genome stability. Biochem Soc Trans. 2005 Dec;33(Pt 6):1456-9. Review. (
  • Gene Review: Bloom's Syndrome (
  • German J, Sanz MM, Ciocci S, Ye TZ, Ellis NA. Syndrome-causing mutations of the BLM gene in persons in the Bloom's Syndrome Registry. Hum Mutat. 2007 Aug;28(8):743-53. (
  • Guo RB, Rigolet P, Ren H, Zhang B, Zhang XD, Dou SX, Wang PY, Amor-Gueret M, Xi XG. Structural and functional analyses of disease-causing missense mutations in Bloom syndrome protein. Nucleic Acids Res. 2007;35(18):6297-310. Epub 2007 Sep 18. (
  • Liu Y, West SC. More complexity to the Bloom's syndrome complex. Genes Dev. 2008 Oct 15;22(20):2737-42. doi: 10.1101/gad.1732808. (
  • NCBI Gene (
  • Ouyang KJ, Woo LL, Ellis NA. Homologous recombination and maintenance of genome integrity: cancer and aging through the prism of human RecQ helicases. Mech Ageing Dev. 2008 Jul-Aug;129(7-8):425-40. doi: 10.1016/j.mad.2008.03.003. Epub 2008 Mar 15. Review. (
  • Singh DK, Ahn B, Bohr VA. Roles of RECQ helicases in recombination based DNA repair, genomic stability and aging. Biogerontology. 2009 Jun;10(3):235-52. doi: 10.1007/s10522-008-9205-z. Epub 2008 Dec 15. Review. (
  • Wu L. Role of the BLM helicase in replication fork management. DNA Repair (Amst). 2007 Jul 1;6(7):936-44. Epub 2007 Mar 23. Review. (


The resources on this site should not be used as a substitute for professional medical care or advice. Users seeking information about a personal genetic disease, syndrome, or condition should consult with a qualified healthcare professional. See How can I find a genetics professional in my area? ( in the Handbook.

Reviewed: November 2010
Published: April 20, 2015