• Test Code:
  • Department:
    Constitutional FISH
  • Test Synonyms:
  • CPT Code(s):

Prader-Willi (PWS) syndrome is characterized by severe hypotonia and feeding difficulties in early infancy, followed in late-infancy/early childhood by excessive eating and obesity.  Developmental delay is common as are hypogonadism and short stature.  Most cases (99%) are caused by absence of a paternal contribution to the imprinted region on chromosome 15q11-q13; approximately 70% of these are due to a large ~5-7 Mb deletion detectable by high resolution chromosome analysis and/or FISH.  The remaining cases include smaller mutations and maternal uniparental disomy – tests for both of these are available in the KDL Molecular Genetics Laboratory.


Slides are prepared per standard protocols.  Ten metaphase cells and 50 interphase cells are scored under fluorescence microscopy.

Specimen Requirements:


  • Adult - 3-5 mL drawn into a GREEN top sodium heparin vacutainer tube or into a pre-heparinized plastic syringe (use 0.2 cc sodium heparin, 1000 unit/mL).  Do NOT use lithium heparin.
  • Child - 1-2 mL, as above.
  • Infant - 1-2 mL, as above. 
  • Keep at room temperature and transport to laboratory as soon as possible.
  • Contact Client Services at (855) 535-1522 for supplies and instructions.

A REQUISITION FORM MUST ACCOMPANY ALL SAMPLES.  Please include detailed clinical information, including ethnicity, clinical history, and family history.

Test Performed (Days):


Turn Around Time:

3-7 days

Shipment Sensitivity Requirements:

Ship via overnight express, using the FedEx priority overnight label provided.  Contact Client Services at (855) 535-1522 for shipping kits and instructions.


Additional Info: