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# Bloom syndrome

A very rare inherited disease with short stature, a sun-sensitive facial rash and a very high risk of cancer at a young age.

Updated 2026-11-01

## Structures involved

Tap one to see what it is and open it in 3D.

- [Skin](https://durgical.com/en/anatomy/skin/)
- [Zygomatic bones](https://durgical.com/en/anatomy/zygomatic-bone/)

## In biochemistry

- [DNA replication: the replication fork](https://durgical.com/en/biochemistry/topics/dna-replication-the-replication-fork/)
- [DNA repair](https://durgical.com/en/biochemistry/topics/dna-repair/)
- [DNA helicases](https://durgical.com/en/biochemistry/enzymes/dna-helicases/)

## Why it happens

- [Cellular aging: telomeres, DNA damage, senescence and proteostasis](https://durgical.com/en/general-pathology/cellular-aging-telomeres-dna-damage-senescence-and-proteostasis/)
- [Genomic instability: mismatch repair, BRCA and xeroderma pigmentosum](https://durgical.com/en/general-pathology/genomic-instability-mismatch-repair-brca-and-xeroderma-pigmentosum/)
- [Hereditary cancer syndromes: the table to know](https://durgical.com/en/general-pathology/hereditary-cancer-syndromes-the-table-to-know/)

## What it is

An autosomal recessive disorder caused by variants in BLM, which encodes a RecQ helicase needed to keep DNA stable during replication and recombination.

## Who gets it

Very rare: only a few hundred cases described, about a third of Ashkenazi Jewish background. No published figures for Colombia.

## Causes

- Biallelic variants in the BLM gene (chromosome 15q26)
- Autosomal recessive inheritance

## Risk factors

- Carrier parents
- Ashkenazi Jewish ancestry (founder variant)
- Consanguinity

## Pathophysiology

BLM helicase, with topoisomerase IIIα, dissolves double Holliday junctions without exchange of material and helps restart stalled replication forks. Without BLM, sister chromatids swap segments about ten times more than normal and recombination between homologous chromosomes rises, causing loss of heterozygosity: a single inherited mutation in a tumour-suppressor gene easily becomes homozygous. That is why many different cancers appear, and early.

## Symptoms and signs

- Proportionate short stature from before birth
- 'Butterfly' facial redness that worsens with sun
- High-pitched voice and narrow face
- Light and dark [skin](https://durgical.com/en/anatomy/skin/) patches
- Frequent respiratory and gut infections
- Male infertility and early menopause

## Red flags

- Lymph node enlargement, fever or pallor (leukaemia or lymphoma)
- Gut bleeding or change in bowel habit in a young adult
- High glucose (early diabetes)

## Diagnosis

**Clinical**
Severe short stature from birth with a photosensitive facial rash.

**Tests**
Markedly increased sister chromatid exchanges in cultured lymphocytes (the characteristic test) and BLM genetic testing.

**Imaging**
No specific findings; ultrasound and MRI are used in tumour surveillance to avoid radiation.

## Treatment

**Lifestyle**
Sun protection to reduce facial lesions.

**Follow-up**
Cancer surveillance from childhood (clinical exam, abdominal ultrasound in childhood, early colonoscopy in adulthood) with minimal radiation.

**Follow-up**
Monitoring of growth, glucose and infections.

**Medical**
If cancer appears, chemotherapy and radiotherapy are reduced because of the hypersensitivity to DNA damage.

**Conservative**
Nutritional support in childhood; short stature responds poorly to growth hormone.

## Complications

- Leukaemias and lymphomas in childhood
- Colon, skin and breast cancers at young ages
- Early type 2 diabetes
- Chronic lung disease
- Infertility

## Prognosis

Life expectancy is reduced, mainly by cancer; many patients develop several different tumours.

## Prevention

- Genetic counselling and carrier testing in at-risk populations

## Test yourself

Think of the answer, then tap the question to see it.

## What kind of protein does the BLM gene encode?

A RecQ family helicase that keeps DNA stable during replication and recombination.

## Which cytogenetic test is characteristic of Bloom syndrome?

A marked increase in sister chromatid exchanges.

## Why do these patients get so many kinds of cancer?

Excess recombination causes loss of heterozygosity and leaves many tumour-suppressor genes without a healthy copy.

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Educational information, not medical advice. For any symptom, see a health professional.

Sources: [Bloom syndrome: MedlinePlus Genetics](https://medlineplus.gov/genetics/condition/bloom-syndrome/) (MedlinePlus, US National Library of Medicine, 2026); [BLM gene: MedlinePlus Genetics](https://medlineplus.gov/genetics/gene/blm/) (MedlinePlus, US National Library of Medicine, 2026); Textbook of Biochemistry for Medical Students, 6th ed. (Jaypee Brothers Medical Publishers (Vasudevan DM, Sreekumari S, Vaidyanathan K), 2011).

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Source: https://durgical.com/en/conditions/bloom-syndrome/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/conditions/bloom-syndrome/