Bloom Syndrome

Bloom Syndrome (BS)

What is Bloom Syndrome (BS)?

Bloom syndrome (OMIM#210900, ORPHA:125) is a multisystem genetic disorder that increases the risk of cancer at all ages. The disease is extremely rare (no available prevalence estimate), except for individuals of Ashkenazi Jewish ancestry, where the prevalence may be about 1 in 48,000. The main clinical manifestations are:

  • Growth deficiency, both at and after birth
  • A characteristic facial appearance is often present, with prominent nose and ears, and mandibular hypoplasia
  • Very sparse subcutaneous fatty tissue
  • Sensitivity to sunlight, that leads to the development of facial erythema
  • Immune abnormalities, with low immunoglobulin serum levels
  • High incidence of hyperglycaemia and diabetes
  • High risk for tumours at all ages, with a tendency to develop at earlier ages compared to the general population. Cancers of different types have been reported in a variety of organs. Based on limited data on patients enrolled in a BS registry, the most common types are haematological malignancies (leukaemias, lymphomas), Wilms tumour in childhood, and, among epithelial cancers, colorectal carcinoma and squamous carcinoma of the head and neck.

What causes Bloom Syndrome?

BS is caused by germline alterations in the BLM gene, that is involved in the maintenance of genomic stability. The disease is diagnosed by clinical manifestations and the detection of alterations in both copies of the BLM gene. A specialized genetic test (sister chromatid exchanges) can also be useful for the diagnosis.

How is Bloom Syndrome inherited?

BS is inherited in an autosomal recessive way, which means that an affected individual has both copies of the BLM gene affected, inherited from parents who are both healthy carriers. The risk of having an affected child for a couple who already has a child with BS is 25% (or 1 in 4). For an individual affected with BS the risk of having an affected child is overall low, since the partner also has to be a carrier. The condition is usually associated with infertility in affected males.Prenatal and preimplantation genetic diagnoses are possible if causative pathogenic variants have been identified in the parents (different legal/ethical perspectives could exist).

What are the surveillance options for Bloom Syndrome?

Individuals should be advised to avoid exposure to sunlight and protect/cover adequately exposed skin. Whenever possible imaging based on use of ionizing radiations should be avoided, due to the presumed cancer risk associated with chromosome instability.


Clinical practice guideline

Currently unavailable


ERN GENTURIS care pathway

Currently unavailable


ERN GENTURIS patient journey

Currently unavailable


ERN GENTURIS publications

Thematic Group 4: Other rare – predominantly malignant – genturis


ERN GENTURIS healthcare providers

A list of healthcare providers with expertise in Thematic Group 4: Other rare - predominantly malignant - genturis can be found here.


Patient associations for hereditary cancer syndromes

A non-exhaustive list of patient associations for genetic tumour risk syndromes in EU member states can be found here.