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Laboratory Test Directory

Prader-Willi/Angelman Syndrome Methylation Analysis


Name Method Department Units
Prader-Willi/Angelman Syndrome Methylation Polymerase chain reaction (PCR)
Agarose gel electrophoresis
Molecular Genetics

Specimen Requirements

Whole blood

Container Type Container Size Specimen Volume

Purple tube (EDTA)

4 mL 4 mL-8 mL

Room temperature - 24 hour(s)
Refrigerated - 72 hour(s)

Specimen Preparation

  • Do not freeze
  • Do not centrifuge
  • Keep at room temperature or refrigerate

Reasons for Rejection

  • Centrifuged specimen
  • Wrong collection tube
  • Clotted specimen
  • Frozen specimen


Please click on the Lab Form Link in the Forms Section to print and complete the Genetic Test Requisition Form. Submission of completed Genetic Test Requisition Form is required, and submission of informed consent form is recommended (but not required).

This test is a SNRPN methylation-specific PCR analysis, and it tests for the presence/absence of maternally-imprinted SNPRPN copy and paternally-imprinted SNRPN copy. This test detects over 99% of Prader-Willi syndrome cases and about 80% of Angelman syndrome cases, including those cases where methylation abnormality is due to deletion, uniparental disomy (UPD), and imprinting center defects.

Prader-Willi syndrome (PWS)/Angelman syndrome (AS) critical region is located within chromosome band 15q11.2-q13 that includes the SNRPN gene. This region is differentially imprinted, with normal individuals having one maternally-imprinted copy and one paternally-imprinted copy of this region. Over 99% of Prader-Willi syndrome is caused by an absence of expression of imprinted genes in the paternally-derived PWS/AS region, and about 80% of Angelman syndrome is caused by an absence of expression of imprinted genes in the maternally-derived PWS/AS region.

If methylation result is abnormal, then additional genetic testing is available to determine the underlying cause of methylation abnormality [e.g. microarray or FISH analysis to test for chromosome 15q11.2-q13 deletion (see test codes SNPMA and FISHON), chromosome 15 UPD analysis (test code UNIDIS)]. In cases of suspected Angelman syndrome, if methylation result from this test is normal, then reflex to UBE3A gene sequencing is available (see test code UBE3A).


Lab Form

CPT Code

  • 81331