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BLM gene

BLM RecQ like helicase

Normal Function

The BLM gene provides instructions for making a member of a protein family called RecQ helicases. Helicases are enzymes that attach (bind) to DNA and unwind the two spiral strands (double helix) of the DNA molecule. This unwinding is necessary for several processes in the cell nucleus, including copying (replicating) DNA in preparation for cell division and repairing damaged DNA. Because RecQ helicases help 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 have two copies of each chromosome, one from each parent. 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 occasionally exchange small sections of DNA during this time, a process called sister chromatid exchange. Researchers suggest that these exchanges may be a response to DNA damage during the copying process. The BLM protein helps to prevent excess sister chromatid exchanges and is also involved in other processes that help maintain the stability of the DNA during the copying process.

Health Conditions Related to Genetic Changes

Bloom syndrome

More than 70 BLM gene mutations have been identified in people with Bloom syndrome, an inherited disorder characterized by short stature, a skin rash that develops after exposure to the sun, and a greatly increased risk of cancer. One particular BLM gene 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. These mutations also reduce the amount of functional BLM protein.

As a result of the lack of functional BLM protein, the frequency of sister chromatid exchange is about 10 times higher than average. Exchange of DNA between chromosomes derived from the individual's mother and father are also increased in people with BLM gene mutations. In addition, chromosome breakage occurs more frequently in affected individuals. All of these changes are associated with gaps and breaks in the genetic material that impair normal cell activities and cause the health problems associated with this condition. Without the BLM protein, the cell is less able to repair DNA damage caused by ultraviolet light, which results in increased sun sensitivity. Genetic changes that allow cells to divide in an uncontrolled way lead to the cancers that occur in people with Bloom syndrome.

More About This Health Condition

Other Names for This Gene

  • Bloom syndrome
  • Bloom syndrome protein
  • Bloom syndrome RecQ like helicase
  • Bloom syndrome, RecQ helicase-like
  • BS
  • MGC126616
  • RECQL3

Additional Information & Resources

Tests Listed in the Genetic Testing Registry

Scientific Articles on PubMed

Catalog of Genes and Diseases from OMIM

Gene and Variant Databases


  • Amor-Gueret M, Dubois-d'Enghien C, Lauge A, Onclercq-Delic R, Barakat A, Chadli E, Bousfiha AA, Benjelloun M, Flori E, Doray B, Laugel V, Lourenco MT, Goncalves 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. Citation on PubMed
  • Amor-Gueret M. Bloom syndrome, genomic instability and cancer: the SOS-like hypothesis. Cancer Lett. 2006 May 8;236(1):1-12. doi: 10.1016/j.canlet.2005.04.023. Epub 2005 Jun 13. Citation on PubMed
  • Arora H, Chacon AH, Choudhary S, McLeod MP, Meshkov L, Nouri K, Izakovic J. Bloom syndrome. Int J Dermatol. 2014 Jul;53(7):798-802. doi: 10.1111/ijd.12408. Epub 2014 Mar 6. Citation on PubMed
  • 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. doi: 10.1101/gad.1609007. Epub 2007 Nov 14. Citation on PubMed or Free article on PubMed Central
  • 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. doi: 10.1042/BST0331456. Citation on PubMed
  • 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. doi: 10.1002/humu.20501. Citation on PubMed
  • 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. doi: 10.1093/nar/gkm536. Epub 2007 Sep 18. Citation on PubMed or Free article on PubMed Central
  • Langer K, Cunniff CM, Kucine N. Bloom Syndrome. 2006 Mar 22 [updated 2023 Oct 12]. In: Adam MP, Feldman J, Mirzaa GM, Pagon RA, Wallace SE, Bean LJH, Gripp KW, Amemiya A, editors. GeneReviews(R) [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2024. Available from Citation on PubMed
  • 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. Citation on PubMed or Free article on PubMed Central
  • 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. Citation on PubMed
  • 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. Citation on PubMed or Free article on PubMed Central
  • Wu L. Role of the BLM helicase in replication fork management. DNA Repair (Amst). 2007 Jul 1;6(7):936-44. doi: 10.1016/j.dnarep.2007.02.007. Epub 2007 Mar 23. Citation on PubMed

The information on this site should not be used as a substitute for professional medical care or advice. Contact a health care provider if you have questions about your health.