Bloom syndrome

2005-02-01   Mounira Amor-Guéret 

Institut Curie - Section de Recherche, UMR 2027 CNRS, Bâtiment 110, Centre Universitaire, F-91405 Orsay Cedex, France



Bloom syndrome


autosomal recessive; frequency is about 2\/105 newborns in Ashkenazi Jews and in the Japanese (founder effect: affected persons descent from a common ancestor); much rarer otherwise
Atlas Image
micronuclei (left); sister chromatid exchange (right) in a normal subject (herein: 19 SCE, instead of the hundred found in Bloom, see below) - Editor






125 Bloom syndrome





168 cases have been registered in the Blooms syndrome Registry by James German; BS patients are predisposed to all types of cancer observed in the general population; thus, BS is a model of initiation and promotion of cancer, and highligths internal causes\/processes of cancers

Phenotype and clinics

- phenotypic spectrum variable.
- growth : dwarfism: intrauterine growth retardation; birth weight: below 2.3 kg; mean length: 44 cm; adult length < 145 cm.
- skin: hyperpigmented (café au lait) spots; hypopigmented areas; sun sensitive telangiectatic erythema; in butterfly configuration across the face: resembles lupus erythematous
- head: microcephaly; dolichocephaly; narrow face; prominent nose and\/or ears; characteristic high-pitched voice
- normal intelligence
- immune deficiency --> frequent infections (may be life-threatening)
- other: myocardopathy; hypogonadism in male patients; hypertriglyceridemia

Neoplastic risk

  • nearly half of patients have had at least one cancer (10% of whom having had more than one primary cancer, which is quite characteristic of Blooms); mean age at first cancer onset: 25 yrs (range: 2-49 yrs)
  • acute leukaemias (ALL and ANLL) in 15 % of cases; lymphomas in 15 % as well; these occur mainly before the thirties
  • carcinomas (of a wide variety) occur in 30 % of cases, mainly after the age of 20 yrs
  • benign tumours (10%)
  • Evolution

    major medical complications apart from cancers are : chronic lung disease, and diabetes mellitus (in 10 %)


    1\/3 of patients are dead at mean age 24 yrs (oldest died at 49 yrs, youngest died before 1 yr) and the mean age of the 2\/3 remaining alive patients is 22 yrs (range: 4-46 yrs)


    Inborn condition

  • chromatid\/chromosome breaks; triradial and quadriradial figures, in particular symetrical quadriradial configuration involving homologous chromosomes (Class I qr), which are pathognomonic and which may be due to a mitotic crossing-over; micronuclei .
  • diagnosis is on the (pathognomonic) highly elevated spontaneous sister chromatid exchange rate (90 SCE per cell; more than 10 times what is normally found); in some persons a minor population of low SCE cells exists, suggesting a recombination event between maternal and paternal alleles (with different mutations), giving rise to a wild type functional gene; this allowed to localize the gene in a very elegant strategy.
  • heterozygotes are not detectable by cytogenetic studies.
  • Atlas Image
    sister chromatid exchange in a normal subject (left) and in a Bloom syndrome patient (right) (from: Mounira Amor-Guéret)

    Other Findings


  • slowing of the cell cycle (lenthening of the G1 and S phases)
  • spontaneous mutation rate 10 times higher than normal cells
  • Genes involved and Proteins

    Complementation groups

    no complementation group


    1417 amino acids; contains one ATP binding site, one DEAH box, and two putative nuclear localization signals


    accumulates to high levels in S phase of the cell cycle, persists in G2\/M and sharply declines in G1; hyperphoshorylated in mitosis


    nuclear (PML nuclear bodies and nucleolus)


  • 3-5 DNA helicase; probable role in DNA replication and double-strand break repair
  • Preferred substrates: G-quadruplex DNA, D-loops structures and X-junctions. Recombinant protein promotes ATP-dependent branch migration of Hollyday junctions.
  • participates in a supercomplex of BRCA1-associated proteins named BASC (BRCA1-Associated genome Surveillance Complex) and in a complex named BRAFT (BLM, RPA, FA, Topoisomerase IIIalpha) containing five of the Fanconia Anemia (FA) complementation group proteins (FANCA, FANCG, FANCC, FANCE and FANCF).
  • Interacts physically and\/or functionally with p53, 53BP1,WRN, MLH1, RAD51, TRF2, ligase IV, FEN1
  • Associated with telomeres and ribosomal DNA repeats.
  • Phosphorylated in mitotic cells through the cdc2 pathway, and in response to DNA damaging agents.
  • Homology

    with the RecQ helicases


    five BLM mutations introducing amino acid substitutions and four BLM mutations introducing premature nonsense codons into the coding sequence have been described to date; one BLM mutation consisting in a 6 bp deletion accompanied by a 7 bp insertion at nucleic acid position 2281 is common in patients from Ashkenazi Jewish ancestry, leading to a truncated protein of 739 amino acids in length; two BLM mutations, 631delCAA and 1610insA were detected in japanese patients.

    To be noted


    135698 BLM


    Pubmed IDLast YearTitleAuthors
    119603802002Bloom's syndrome protein response to ultraviolet-C radiation and hydroxyurea-mediated DNA synthesis inhibition.Ababou M et al
    108621052000Identification of a novel BLM missense mutation (2706T>C) in a Moroccan patient with Bloom's syndrome.Barakat A et al
    156042582004A major role for mitotic CDC2 kinase inactivation in the establishment of the mitotic DNA damage checkpoint.Bayart E et al
    113094172001Regulation and localization of the Bloom syndrome protein in response to DNA damage.Bischof O et al
    108510732000Cell cycle regulation of the endogenous wild type Bloom's syndrome DNA helicase.Dutertre S et al
    88752521996Molecular genetics of Bloom's syndrome.Ellis NA et al
    75859681995The Bloom's syndrome gene product is homologous to RecQ helicases.Ellis NA et al
    92857781997Characterization of a new BLM mutation associated with a topoisomerase II alpha defect in a patient with Bloom's syndrome.Foucault F et al
    117818422001The Bloom syndrome protein interacts and cooperates with p53 in regulation of transcription and cell growth control.Garkavtsev IV et al
    119711872002Increased error-prone non homologous DNA end-joining--a proposed mechanism of chromosomal instability in Bloom's syndrome.Gaymes TJ et al
    90625851997Bloom's syndrome. XX. The first 100 cancers.German J et al
    105255301999PML is critical for ND10 formation and recruits the PML-interacting protein daxx to this nuclear structure when modified by SUMO-1.Ishov AM et al
    152898972004Relatively common mutations of the Bloom syndrome gene in the Japanese population.Kaneko H et al
    93884801997BLM (the causative gene of Bloom syndrome) protein translocation into the nucleus by a nuclear localization signal.Kaneko H et al
    93881931997The Bloom's syndrome gene product is a 3'-5' DNA helicase.Karow JK et al
    108238972000The Bloom's syndrome gene product promotes branch migration of holliday junctions.Karow JK et al
    120191522002The BLM helicase is necessary for normal DNA double-strand break repair.Langland G et al
    127244012003A multiprotein nuclear complex connects Fanconi anemia and Bloom syndrome.Meetei AR et al
    114330312001The Bloom's and Werner's syndrome proteins are DNA structure-specific helicases.Mohaghegh P et al
    145763162003Possible anti-recombinogenic role of Bloom's syndrome helicase in double-strand break processing.Onclercq-Delic R et al
    121813132002Telomere-binding protein TRF2 binds to and stimulates the Werner and Bloom syndrome helicases.Opresko PL et al
    116919252001Direct association of Bloom's syndrome gene product with the human mismatch repair protein MLH1.Pedrazzi G et al
    145778412003Telomere and ribosomal DNA repeats are chromosomal targets of the bloom syndrome DNA helicase.Schawalder J et al
    153649582004Functional interaction between BLM helicase and 53BP1 in a Chk1-mediated pathway during S-phase arrest.Sengupta S et al
    155095772004Genetic interactions between BLM and DNA ligase IV in human cells.So S et al
    124440982002The Bloom syndrome helicase BLM interacts with TRF2 in ALT cells and promotes telomeric DNA synthesis.Stavropoulos DJ et al
    97652921998The Bloom's syndrome helicase unwinds G4 DNA.Sun H et al
    155799052005Human Bloom protein stimulates flap endonuclease 1 activity by resolving DNA secondary structure.Wang W et al
    113997662001Functional interaction of p53 and BLM DNA helicase in apoptosis.Wang XW et al
    107831652000BASC, a super complex of BRCA1-associated proteins involved in the recognition and repair of aberrant DNA structures.Wang Y et al
    112785092001Potential role for the BLM helicase in recombinational repair via a conserved interaction with RAD51.Wu L et al
    120800662002The processing of Holliday junctions by BLM and WRN helicases is regulated by p53.Yang Q et al
    107795602000Nuclear structure in normal and Bloom syndrome cells.Yankiwski V et al
    110874182000Binding and melting of D-loops by the Bloom syndrome helicase.van Brabant AJ et al
    119191942002Colocalization, physical, and functional interaction between Werner and Bloom syndrome proteins.von Kobbe C et al