Prader-Willi Syndrome

Test Overview

CPT Code(s)

Peripheral Blood: 88230-52, 88271, 88273, 88291

Amniotic Fluid: 88235-52, 88271, 88273, 88291



Specimen Requirements

Specimen RequirementsPeripheral BloodAmniotic Fluid
ContainerSodium Heparin (green top tube)Two 15 ml sterile leak-proof conical tubes
Optimal Quantity2-3 ml20-25 ml
Minimum Quantity1-2 ml10 ml
StorageRoom TemperatureRoom Temperature
Stability at Room TemperatureRoom Temperature for 8 hours, then refrigerateRoom Temperature for 8 hours, then refrigerate
TransportationAvoid freezing or heating over 35oCAvoid freezing or heating over 35oC

Turnaround Time

Peripheral Blood: Final report in 5 days for 90% of cases

Amniotic Fluid: Final report in 7-10 days for 90% of cases

Test Details

Clinical Significance

Fluorescence in situ hybridization (FISH) is a sensitive method to detect smaller genomic changes associated with various micordeletion syndromes.  There are several advantages with FISH technology over routine chromosome analysis and such advantages include the ability of FISH technology to detect genomic abnormalities in non-viable and non-dividing tissues, rapid turnaround time, and increased resolution.  However, FISH technology is complementary to routine chromosome analysis and cannot substitute routine chromosome analysis and FISH diagnostic testing is not recommended as an isolated test without chromosome analysis for the diagnosis of these microdeletion syndromes.

Clinical Background

Prader-Willi syndrome, caused by microdeletions/loss of paternally derived gene expression, is a panethnic developmental disorder affecting approximately 1 in 10,000 to 1 in 15,000 live births. Patients with this syndrome show characteristic features including unusual facial appearance, short stature, severe mental retardation, spasticity and seizures.  Chromosome deletion 15q11q13 during male meiosis results in Prader-Willi syndrome and such deletions account for a large number of patients while a small number of patients have mutations within this gene that cannot be detected by either routine chromosome analysis or FISH.   Since the most common deletion encompasses ~3 Mb, often these deletions are not detected on routine chromosome analysis.  FISH is the ideal choice for detection of this deletion due to its increased sensitivity.


The sample is usually cultured until sufficient number of mitotic cells is observed (48-72 hours for peripheral blood and 7-10 days for amniotic fluid) and after harvesting the cells are hybridized with the probes.  After hybridization and post-hybridization washes, the slides are analyzed under a fluorescence microscope equipped with epifluorescence and appropriate filter sets.  Analysis and scoring is carried out by two certified technologists in a blinded fashion with each scoring a minimum of 5 metaphases and 50 interphase nuclei.  Results are reviewed by both the laboratory manager and the director.

15q11 deletion (Prader-Willi syndrome) SNRPN / 154P1             Cytocell (cat # LPU005)

Interpretation of Results

The morphologic interpretation and correlation of results on all cases is performed by a board-certified doctoral level scientist (laboratory director). The final report has a narrative description of results.  If abnormalities are present, they are explained in a paragraph which helps to clarify and correlate chromosomal findings with phenotype. References are included in the report to help the referring physician with interpretation, which include books or journals that contain appropriate information. Recommendations are made as to any additional testing, if necessary.