FISH ANALYSIS, PRADER-WILLI SYNDROME
Chromosomal Locus: 15q11.2
Pseudonyms: 15q11.2 deletion, SNRPN gene deletion
TURNAROUND TIME: 7 to 10 days
Fluorescence in situ hybridization
- Collect: 3-5 mL peripheral blood in sodium heparin (green) for children and adults; 1-2 mL peripheral blood in sodium heparin (green) for newborns
- Min. Collection: 1 mL for newborns; 2 mL for children and adults
- Transport: peripheral blood in sodium heparin (green) at 20-25°C
- Stability: Ambient: 24 hours; Refrigerated: 72 hours; Frozen: unacceptable
- Unacceptable Conditions: Frozen or clotted specimens; specimens in anticoagulants other than sodium heparin.
Test Summary: Test can detect microdeletions of the SNRPN gene on chromosome 15. Approximately 70% of patients with Prader-Willi syndrome (PWS) have deletions of the PWS critical region including the SNRPN gene detectable by FISH.
Methods: A triple-color FISH analysis performed on metaphase cells using probes for the SNRPN locus (15q11.2) and for the D15Z1 and the PML loci (controls); analysis of 10 metaphase cells and 20 interphase cells
Test Limitations: The test does not detect other causes of Prader-Willi Syndrome such as maternal uniparental disomy or imprinting defects.
Indications for Use:
- Patients suspected of having Prader-Willi syndrome on the basis of clinical findings such as neonatal hypotonia and failure to thrive, short stature, hypogonadotropic hypogonadism, developmental delay, and early childhood onset hyperphagia resulting in obesity
- Patients with a positive DNA methylation test for Prader-Willi syndrome