Bloom syndrome is an autosomal recessive chromosomal-instability syndrome caused by biallelic loss-of-function variants in BLM, which encodes a RecQ helicase. Defective BLM function impairs genome maintenance, causing excessive homologous recombination, high levels of sister chromatid exchange, and broad chromosome instability. The clinical phenotype includes prenatal and postnatal growth deficiency, photosensitive skin changes, immune dysfunction, recurrent infections, insulin resistance or diabetes, infertility, and a greatly increased risk of early-onset and multiple cancers.
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Conditions with similar clinical presentations that must be differentiated from Bloom syndrome:
name: Bloom syndrome
creation_date: '2026-04-11T19:38:25Z'
updated_date: '2026-04-12T00:26:00Z'
category: Mendelian
description: >-
Bloom syndrome is an autosomal recessive chromosomal-instability syndrome
caused by biallelic loss-of-function variants in BLM, which encodes a RecQ
helicase. Defective BLM function impairs genome maintenance, causing excessive
homologous recombination, high levels of sister chromatid exchange, and broad
chromosome instability. The clinical phenotype includes prenatal and postnatal
growth deficiency, photosensitive skin changes, immune dysfunction, recurrent
infections, insulin resistance or diabetes, infertility, and a greatly
increased risk of early-onset and multiple cancers.
disease_term:
preferred_term: Bloom syndrome
term:
id: MONDO:0008876
label: Bloom syndrome
mappings:
mondo_mappings:
- term:
id: MONDO:0008876
label: Bloom syndrome
mapping_predicate: skos:exactMatch
mapping_source: MONDO
parents:
- chromosomal instability syndrome
- hereditary disease
synonyms:
- Bloom's syndrome
inheritance:
- name: Autosomal recessive inheritance
inheritance_term:
preferred_term: Autosomal recessive inheritance
term:
id: HP:0000007
label: Autosomal recessive inheritance
description: >-
Bloom syndrome is inherited as an autosomal recessive disorder caused by
biallelic pathogenic variants in BLM.
evidence:
- reference: PMID:28232778
reference_title: "Bloom's Syndrome: Clinical Spectrum, Molecular Pathogenesis, and Cancer Predisposition."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Bloom's syndrome is an autosomal recessive disorder characterized by prenatal and postnatal growth deficiency, photosensitive skin changes, immune deficiency, insulin resistance, and a greatly increased risk of early onset of cancer and for the development of multiple cancers.
explanation: >-
This review directly states the recessive inheritance pattern.
pathophysiology:
- name: BLM helicase deficiency
description: >-
Bloom syndrome results from loss of the BLM RecQ helicase, a central genome
maintenance factor.
genes:
- preferred_term: BLM
term:
id: hgnc:1058
label: BLM
biological_processes:
- preferred_term: DNA repair
modifier: DECREASED
term:
id: GO:0006281
label: DNA repair
evidence:
- reference: PMID:28232778
reference_title: "Bloom's Syndrome: Clinical Spectrum, Molecular Pathogenesis, and Cancer Predisposition."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Loss-of-function mutations of BLM, which codes for a RecQ helicase, cause Bloom's syndrome.
explanation: >-
This directly identifies the core molecular lesion in Bloom syndrome.
downstream:
- target: Excessive homologous recombination
description: Loss of BLM disrupts replication-associated genome surveillance
- name: Excessive homologous recombination
description: >-
Loss of BLM causes excessive homologous recombination during genome
maintenance.
biological_processes:
- preferred_term: double-strand break repair via homologous recombination
modifier: ABNORMAL
term:
id: GO:0000724
label: double-strand break repair via homologous recombination
evidence:
- reference: PMID:28232778
reference_title: "Bloom's Syndrome: Clinical Spectrum, Molecular Pathogenesis, and Cancer Predisposition."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
The absence of a functional BLM protein causes chromosome instability, excessive homologous recombination, and a greatly increased number of sister chromatid exchanges that are pathognomonic of the syndrome.
explanation: >-
This sentence directly supports dysregulated homologous recombination as a
central genome-maintenance defect.
downstream:
- target: Pathologic sister chromatid exchange
description: Excessive homologous recombination produces the pathognomonic sister chromatid exchange phenotype
- name: Pathologic sister chromatid exchange
description: >-
Excessive recombination in Bloom syndrome produces strikingly elevated sister
chromatid exchange.
evidence:
- reference: PMID:28232778
reference_title: "Bloom's Syndrome: Clinical Spectrum, Molecular Pathogenesis, and Cancer Predisposition."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
The absence of a functional BLM protein causes chromosome instability, excessive homologous recombination, and a greatly increased number of sister chromatid exchanges that are pathognomonic of the syndrome.
explanation: >-
This directly supports pathologic sister chromatid exchange as a discrete
downstream consequence of BLM deficiency.
- reference: PMID:25794620
reference_title: "TopBP1 interacts with BLM to maintain genome stability but is dispensable for preventing BLM degradation."
supports: PARTIAL
evidence_source: IN_VITRO
snippet: >-
However, BLM-TopBP1 binding is important for maintaining genome integrity, because in its absence cells display increased sister chromatid exchanges, replication origin firing and chromosomal aberrations.
explanation: >-
This cell-based mechanistic study provides direct support that disrupted
BLM-associated regulation drives sister chromatid exchange and chromosomal
instability.
downstream:
- target: Broad chromosomal instability
description: Persistent sister chromatid exchange contributes to broader chromosome-level instability
- name: Broad chromosomal instability
description: >-
Persistent genome-maintenance failure produces broader chromosomal
instability beyond sister chromatid exchange alone.
evidence:
- reference: PMID:25794620
reference_title: "TopBP1 interacts with BLM to maintain genome stability but is dispensable for preventing BLM degradation."
supports: PARTIAL
evidence_source: IN_VITRO
snippet: >-
However, BLM-TopBP1 binding is important for maintaining genome integrity, because in its absence cells display increased sister chromatid exchanges, replication origin firing and chromosomal aberrations.
explanation: >-
This supports a broader chromosome-instability state downstream of impaired
BLM-associated regulation.
downstream:
- target: Somatic mutation accumulation and cancer predisposition
description: Chromosomal instability increases somatic mutation burden and malignant transformation risk
- name: Somatic mutation accumulation and cancer predisposition
description: >-
Ongoing chromosomal instability increases somatic mutation burden and drives
the marked early-onset cancer predisposition of Bloom syndrome.
evidence:
- reference: PMID:28232778
reference_title: "Bloom's Syndrome: Clinical Spectrum, Molecular Pathogenesis, and Cancer Predisposition."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Bloom's syndrome is a prototypical chromosomal instability syndrome, and the somatic mutations that occur as a result of that instability are responsible for the increased cancer risk.
explanation: >-
This review explicitly connects genome instability to cancer risk in Bloom
syndrome.
phenotypes:
- name: Short stature
category: Growth
description: >-
Prenatal and postnatal growth deficiency are major clinical hallmarks of
Bloom syndrome.
phenotype_term:
preferred_term: Short stature
term:
id: HP:0004322
label: Short stature
evidence:
- reference: PMID:28232778
reference_title: "Bloom's Syndrome: Clinical Spectrum, Molecular Pathogenesis, and Cancer Predisposition."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Bloom's syndrome is an autosomal recessive disorder characterized by prenatal and postnatal growth deficiency, photosensitive skin changes, immune deficiency, insulin resistance, and a greatly increased risk of early onset of cancer and for the development of multiple cancers.
explanation: >-
This directly documents the characteristic growth-deficiency phenotype.
- name: Photosensitivity
category: Dermatologic
description: >-
Photosensitive skin changes are a classic and frequently recognized
manifestation of Bloom syndrome.
phenotype_term:
preferred_term: Cutaneous photosensitivity
term:
id: HP:0000992
label: Cutaneous photosensitivity
evidence:
- reference: PMID:28232778
reference_title: "Bloom's Syndrome: Clinical Spectrum, Molecular Pathogenesis, and Cancer Predisposition."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Bloom's syndrome is an autosomal recessive disorder characterized by prenatal and postnatal growth deficiency, photosensitive skin changes, immune deficiency, insulin resistance, and a greatly increased risk of early onset of cancer and for the development of multiple cancers.
explanation: >-
The review explicitly lists photosensitive skin changes among the defining
manifestations.
- name: Immunodeficiency
category: Immunologic
description: >-
Immune dysfunction contributes to recurrent infection susceptibility in
Bloom syndrome.
phenotype_term:
preferred_term: Immunodeficiency
term:
id: HP:0002721
label: Immunodeficiency
evidence:
- reference: PMID:28232778
reference_title: "Bloom's Syndrome: Clinical Spectrum, Molecular Pathogenesis, and Cancer Predisposition."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Bloom's syndrome is an autosomal recessive disorder characterized by prenatal and postnatal growth deficiency, photosensitive skin changes, immune deficiency, insulin resistance, and a greatly increased risk of early onset of cancer and for the development of multiple cancers.
explanation: >-
This directly identifies immune deficiency as part of the syndrome.
- name: Diabetes mellitus
category: Endocrine
description: >-
Insulin resistance and overt diabetes are recognized metabolic complications
of Bloom syndrome.
phenotype_term:
preferred_term: Diabetes mellitus
term:
id: HP:0000819
label: Diabetes mellitus
evidence:
- reference: PMID:28232778
reference_title: "Bloom's Syndrome: Clinical Spectrum, Molecular Pathogenesis, and Cancer Predisposition."
supports: PARTIAL
evidence_source: HUMAN_CLINICAL
snippet: >-
Bloom's syndrome is an autosomal recessive disorder characterized by prenatal and postnatal growth deficiency, photosensitive skin changes, immune deficiency, insulin resistance, and a greatly increased risk of early onset of cancer and for the development of multiple cancers.
explanation: >-
The abstract states insulin resistance directly; this provides partial
support for the related, downstream phenotype of diabetes mellitus.
- name: Neoplasm
category: Oncology
description: >-
Bloom syndrome carries a striking predisposition to early-onset and multiple
malignancies.
phenotype_term:
preferred_term: Neoplasm
term:
id: HP:0002664
label: Neoplasm
evidence:
- reference: PMID:28232778
reference_title: "Bloom's Syndrome: Clinical Spectrum, Molecular Pathogenesis, and Cancer Predisposition."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Bloom's syndrome is an autosomal recessive disorder characterized by prenatal and postnatal growth deficiency, photosensitive skin changes, immune deficiency, insulin resistance, and a greatly increased risk of early onset of cancer and for the development of multiple cancers.
explanation: >-
This review directly supports strong cancer predisposition in Bloom
syndrome.
genetic:
- name: BLM
association: Loss-of-function
gene_term:
preferred_term: BLM
term:
id: hgnc:1058
label: BLM
notes: >-
Biallelic BLM loss-of-function variants disable the Bloom syndrome helicase
and drive the syndrome's chromosomal-instability phenotype.
evidence:
- reference: PMID:28232778
reference_title: "Bloom's Syndrome: Clinical Spectrum, Molecular Pathogenesis, and Cancer Predisposition."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Loss-of-function mutations of BLM, which codes for a RecQ helicase, cause Bloom's syndrome.
explanation: >-
This directly states that BLM loss of function is the genetic cause.
- reference: CGGV:assertion_e0a20b67-5a62-462c-894b-76b60a66e979-2019-04-19T160000.000Z
reference_title: "BLM / Bloom syndrome (Definitive)"
supports: SUPPORT
evidence_source: OTHER
snippet: "BLM | HGNC:1058 | Bloom syndrome | MONDO:0008876 | AR | Definitive"
explanation: ClinGen classifies the BLM-Bloom syndrome gene-disease relationship as definitive with autosomal recessive inheritance.
treatments:
- name: Sun protection
description: >-
Avoidance of ultraviolet exposure is recommended to reduce photosensitive
skin manifestations.
treatment_term:
preferred_term: supportive care
term:
id: MAXO:0000950
label: supportive care
evidence:
- reference: PMID:28232778
reference_title: "Bloom's Syndrome: Clinical Spectrum, Molecular Pathogenesis, and Cancer Predisposition."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Although there is currently no treatment aimed at the underlying genetic abnormality, persons with Bloom's syndrome benefit from sun protection, aggressive treatment of infections, surveillance for insulin resistance, and early identification of cancer.
explanation: >-
The review explicitly identifies sun protection as a beneficial management
strategy.
- name: Infection management
description: >-
Recurrent infections should be treated aggressively because of the syndrome's
immune dysfunction.
treatment_term:
preferred_term: Pharmacotherapy
term:
id: NCIT:C15986
label: Pharmacotherapy
evidence:
- reference: PMID:28232778
reference_title: "Bloom's Syndrome: Clinical Spectrum, Molecular Pathogenesis, and Cancer Predisposition."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Although there is currently no treatment aimed at the underlying genetic abnormality, persons with Bloom's syndrome benefit from sun protection, aggressive treatment of infections, surveillance for insulin resistance, and early identification of cancer.
explanation: >-
The review directly includes aggressive treatment of infections as part of
standard management.
- name: Metabolic surveillance
description: >-
Ongoing monitoring for insulin resistance and diabetes is part of routine
care in Bloom syndrome.
treatment_term:
preferred_term: supportive care
term:
id: MAXO:0000950
label: supportive care
evidence:
- reference: PMID:28232778
reference_title: "Bloom's Syndrome: Clinical Spectrum, Molecular Pathogenesis, and Cancer Predisposition."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Although there is currently no treatment aimed at the underlying genetic abnormality, persons with Bloom's syndrome benefit from sun protection, aggressive treatment of infections, surveillance for insulin resistance, and early identification of cancer.
explanation: >-
This directly supports surveillance for metabolic complications.
- name: Cancer surveillance
description: >-
Early identification of malignancy is a core management strategy because of
the marked cancer predisposition.
treatment_term:
preferred_term: supportive care
term:
id: MAXO:0000950
label: supportive care
evidence:
- reference: PMID:28232778
reference_title: "Bloom's Syndrome: Clinical Spectrum, Molecular Pathogenesis, and Cancer Predisposition."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Although there is currently no treatment aimed at the underlying genetic abnormality, persons with Bloom's syndrome benefit from sun protection, aggressive treatment of infections, surveillance for insulin resistance, and early identification of cancer.
explanation: >-
This directly supports malignancy surveillance as part of current care.
differential_diagnoses:
- name: Fanconi anemia
disease_term:
preferred_term: Fanconi anemia
term:
id: MONDO:0019391
label: Fanconi anemia
description: >-
Fanconi anemia overlaps with Bloom syndrome through chromosome instability,
cancer predisposition, growth deficiency, and bone marrow complications, but
is distinguished by DNA crosslink-repair defects and more prominent marrow
failure.
distinguishing_features:
- Pathognomonic sister chromatid exchange favors Bloom syndrome.
- Bone marrow failure and congenital radial-ray anomalies favor Fanconi anemia.
- name: Nijmegen breakage syndrome
disease_term:
preferred_term: Nijmegen breakage syndrome
term:
id: MONDO:0009623
label: Nijmegen breakage syndrome
description: >-
Nijmegen breakage syndrome is another DNA-repair disorder with
immunodeficiency and cancer predisposition, but it is usually distinguished
by microcephaly and double-strand break-repair abnormalities rather than the
characteristic Bloom sister chromatid exchange phenotype.
distinguishing_features:
- Marked photosensitivity and elevated sister chromatid exchange favor Bloom syndrome.
- Microcephaly and radiosensitivity favor Nijmegen breakage syndrome.
clinical_trials: []
datasets: []
notes: >-
Asta deep research was run as requested, but final curation relied on direct
review of primary PubMed sources because the retrieval output was noisy and
only partially disease-specific.
This report is retrieval-only and is generated directly from Asta results.
search_papers_by_relevance with snippet_search.