Skip Navigation
Genetics Home Reference: your guide to understanding genetic conditions About   Site Map   Contact Us
Home A service of the U.S. National Library of Medicine®
Printer-friendly version


Reviewed April 2015

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.

Read more about gene names and symbols on the About page.

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 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.

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, 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.

Where is the BLM gene located?

Cytogenetic Location: 15q26.1

Molecular Location on chromosome 15: base pairs 90,717,327 to 90,815,462

(Homo sapiens Annotation Release 107, GRCh38.p2) (NCBIThis link leads to a site outside Genetics Home Reference.)

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 90,717,327 to base pair 90,815,462 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

Where can I find general information about genes?

The Handbook provides basic information about genetics in clear language.

These links provide additional genetics resources that may be useful.

What glossary definitions help with understanding BLM?

acids ; cancer ; cell ; cell division ; cell nucleus ; chromatid ; chromosome ; DNA ; DNA damage ; double helix ; gene ; genome ; helicase ; inherited ; molecule ; mutation ; nucleus ; protein ; protein sequence ; sensitivity ; short stature ; sister chromatid ; sister chromatid exchange ; stature ; sun sensitivity ; syndrome

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

See also Understanding Medical Terminology.

References (14 links)


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: April 2015
Published: February 1, 2016