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Prader-Willi Syndrome deletion 15q11 by FISH*

Test Code


Test Synonyms

del(15)(q11.2q13), Microdeletion syndrome


deletion 15q11


Fluorescence in situ Hybridization (FISH)
*Performed by affiliate laboratory

Turnaround Time

7-9 days

Specimen Requirements

5mL peripheral blood in sodium heparin
3mL bone marrow in sodium heparin
Fixed cytogenetically prepared cells in sterile centrifuge tube with pellet visible in 3:1, Methanol:Acetic Acid

Specimen Stability
Blood and bone marrow = 4°C to 25°C, specimens are stable up to 72 hours
Fixed cell pellets are stable for years when stored at -28°C to 15°C
Storage & Handling

4°C to 25°C during transit, but specimens may be transported on refrigerated gel packs. Do not allow the gel pack to come in contact with the specimen. Do not freeze. Extreme temperatures should be avoided.

Causes for Rejection

Clotted specimen; Specimen exposed to extreme temperature; Anticoagulant toxic to cells; Insufficient number of cells

Reference Range

See report

It is recommended that all FISH studies be done in conjunction with routine cytogenetic studies. If the FISH result is normal, a chromosome analysis allows identification of more complex abnormalities.


Prader-Willi syndrome (PWS), a rare neurogenetic disorder, represents the most common syndromatic obesity. Loss of the paternal genes on a specific region of chromosome 15 is the cause of this syndrome. Either two copies of the maternal genes is inherited (uniparental disomy) causing the loss of the paternal segment or there occurs a deletion of the genes on the paternal chromosome 15. The deletion can be detected by FISH, but specialized genetic testing is necessary to distinguish from Angelman syndrome.

  1. Bittel DC, Butler MG. (2005). Prader-Willi syndrome: clinical genetics, cytogenetics and molecular biology. Expert Rev Mol Med.7(14):1-20.
  2. Borelina D et al. (2004). Combined cytogenetic and molecular analyses for the diagnosis of Prader-Willi/Angelman syndromes. J Biochem Mol Biol. 37(5):522-6.