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BLM gene
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Gene

BLM gene

The BLM gene provides instructions for creating a protein essential for maintaining genomic stability and repairing damaged DNA.

Normal Function

The BLM gene provides instructions for making a member of a protein family called RecQ helicases. Helicases are enzymes that attach to DNA and unwind the two spiral strands 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, the DNA that makes up the chromosomes is copied. 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, 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 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 mutation, known as blmAsh, causes almost all cases of Bloom syndrome among people of Central and Eastern European (Ashkenazi) Jewish descent. This mutation deletes six DNA building blocks and replaces them with seven others, resulting in an abnormally short, nonfunctional version of the BLM protein.

As a result of the lack of functional BLM protein, the following cellular changes occur:

  • The frequency of sister chromatid exchange is about 10 times higher than average.
  • Exchange of DNA between chromosomes derived from the mother and father is increased.
  • Chromosome breakage occurs more frequently.
  • Cells are less able to repair DNA damage caused by ultraviolet light, resulting in increased sun sensitivity.
  • Genetic changes that allow cells to divide in an uncontrolled way lead to the cancers associated with this condition.

Other Names for This Gene

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

Frequently Asked Questions

Cancer screening begins in childhood and early adulthood because BLM mutations predispose individuals to virtually all cancer types at exceptionally young ages. Protocols include frequent full-body skin checks, abdominal imaging, early gastrointestinal endoscopy and colonoscopy (often starting between ages 10 and 15 or in early adulthood), and early breast cancer screening with annual breast MRI starting at age 25.
Mutations in the BLM gene impair the cell's ability to repair DNA damage caused by ultraviolet (UV) radiation. Sun exposure triggers severe skin erythema, telangiectatic butterfly-pattern rashes across the cheeks and nose, and an elevated risk for developing early skin cancers. Daily broad-spectrum SPF 50+ sunscreen, UV-protective clothing, wide-brimmed hats, and avoidance of midday outdoor activity are required lifelong.
In addition to targeted BLM gene sequencing, a classic cytogenetic test called the sister chromatid exchange (SCE) assay is performed. When cultured blood lymphocytes or fibroblasts are exposed to bromodeoxyuridine, cells with Bloom syndrome exhibit a characteristically high frequency of sister chromatid exchanges (often ten times higher than normal), confirming the defect in genomic maintenance.
Because cells lacking functional BLM protein cannot efficiently repair double-strand DNA breaks, patients are hypersensitive to ionizing radiation and alkylating or DNA-damaging chemotherapy drugs. Clinicians must minimize diagnostic X-rays and CT scans, avoid therapeutic radiation when possible, and administer substantially reduced chemotherapy doses under close hematologic and oncologic supervision.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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