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Genetic counseling: Bloom Syndrome-1

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Bloom Syndrome

GeneticsEdit

  • Mutation of BLM gene at chromosome 15q26.1
  • Common Ashkenazi Jewish mutation- blmASH (2281del6ins7)
  • Abnormalities in DNA repair and chromosomal structure
    • increased chromosome breakage
    • increased rate of homologous chromosome exchange
    • formation of quadriradial (QR) configuration in mitosis
    • increased rate of sister chromatid exchanges (SCEs)
    • unique to Bloom Syndrome

IncidenceEdit

  • Ashkenazi Jewish population
  • Carrier frequency 1 in 107
  • Incidence 1/160,000
  • Very rare in Non-Ashkenazi Jewish populations

DiagnosisEdit

  • Characteristic clinical features
  • Demonstration of symmetric QR interchange configuration and increased number

of SCEs

  • Demonstration of mutations in both BLM genes

Clinical FeaturesEdit

  • Predominant features
    • Small body size
      • Mean birth weight 1906 g in males and 1810 g in females
      • Mean adult height 147.5 cm in males and 138.6 cm in females
    • Predisposition to cancer- of all cell types and at all sites
  • Additional features which may or may not be present
    • Characteristic facies- keel-shaped face, dolicocephaly, narrow cranium, malar hypoplasia, nasal prominence, small mandible, and prominent ears.
    • Hypersensitivity to sunlight- formation of sun-sensitive erythema (telangiectasia) on face and possible hands/forearms
    • Areas of hyper- and hypo- pigmented skin- café-au-lait spots
    • High-pitched and somewhat squeaky voice
    • Vomiting and diarrhea during infancy
    • Diabetes mellitus- generally with onset in the second or third decade
    • Failure of spermatogenesis in males
    • Early cessation of menstruation and reduced fertility in females
    • General immunodeficiency- often associated with ottitis media and pneumonia
    • Slightly increased incidence of minor anatomic anomalies including anomalous digits, pilonidal dimples, wedges of altered color of the irides, and obstructing anomalies of the urethra
    • Restricted intellectual ability- generally average to low-average intelligence but can be more severe

Natural HistoryEdit

  • Intrauterine Growth Deficiency
  • full-term infants tend to have low birth weight
  • Onset of facial skin lesion usually in first or second summer, can be later
  • Cancer predisposition throughout life- always higher than age-associated risk
  • Mean age of cancer diagnosis 24.7 (range of 2 to 48 years)
  • Mean age of death is 23.6 years (range from <1 to 49)
  • Cancer is the most common cause of death

InheritanceEdit

  • Autosomal Recessive

TestingEdit

  • Cytogenic analysis
  • Increased in number or chromatid gaps, breaks, and interchanges
  • Increase in the number of sister-chromatid exchanges (SCEs)
  • Can be performed on any cell which can be brought into mitosis
  • Molecular Genetic Analysis
  • Clinical testing for common Ashkenazi Jewish mutation- blmASH
  • 98% detection for Ashkenazi Jewish Bloom syndrome patients
  • Research testing - full gene screening for affected individuals
  • Memorial Sloan-Kettering Cancer Center
  • Prenatal diagnosis
  • Sister chromatid exchange assay via amnio or CVS
  • Amnio or CVS for known familial mutation

Management & TreatmentEdit

  • No treatment for growth deficiency
  • Protection from the sun decreases severity of skin lesion
  • Careful monitoring for cancer
  • Cancer treatment must consider hypersensitivity to DNA-damaging chemicals

Differential DiagnosisEdit

  • Other syndromes associated with sun sensitivity and telangiectasias:
  • Erythropoietic protoporphyria
  • Rothmund-Thomson syndrome
  • Cockayne syndomre
  • Hereditary hemorrhagic telangiectasia
  • Ataxia telangiectasia

Psychosocial IssuesEdit

  • Physical appearance may affect self-image, confidence
  • Reduced life expectancy
  • High probability of malignancy

Patient ResourcesEdit

  • Bloom's Syndrome Registry
NY Blood Center
310 East 67th Street
New York, NY 10021
Phone: (212) 570-3075
  • National Foundation for Jewish Genetic Diseases, Inc. (NFJGD)
250 Park Ave, Suite 1000
New York, NY 10177
Phone: (212) 371-1030
Web
  • Xeroderma Pigmentosum Society, Inc.
Box 4759
Poughkeepsie, NY 12602
Phone: (518) 851-2612
Web
E-mail: xps@xps.org

Case SpecificsEdit

  • See attached

ReferencesEdit

  • Byarlay, J. and Goldsmith, L. (1997) Other Genetic Disorders of the Skin. In Rimoin, D, Connor, J, and Pueritz, R ed. Principles and Practice of Medical Genetics. Churchill Livingstone: New York. 1309-1310.
  • German, J. and Ellis, N. (2001). Bloom Syndrome. In Scriver, C., Beaudet, A., Sly, W., and Velle, D. ed. Metabolic and Molecular Bases of Inherited Disease. McGraw Hill: New York. 733-751.
  • Goodman, R. (1979) Genetic Disorders among the Jewish People. Johns Hopkins

University Press: Baltimore. 73-79.

NotesEdit

The information in this outline was last updated in March 2003.


Material obtained under GFDL Licence from http://en.wikibooks.org/wiki/Handbook_of_Genetic_Counseling

Heckert GNU white Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled "GNU Free Documentation License."

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