Background:
Prader-Willi (PWS) syndrome is a rare imprinting disorder characterized by severe hypotonia and feeding difficulties in early infancy, followed by excessive eating and obesity in late-infancy/early childhood (Miller et al. 2011). Developmental delay, hypogonadism and short stature are also common features (Duis et al. 2019). Signature behaviors of individuals with PWS include tantrums, obsessive–compulsive tendencies, autistic‐like features, and skin picking. Most cases are caused by the loss of paternally expressed genes on chromosome 15q11.2-q13. The loss of imprinting may be caused by a large deletion of the paternal 15q11.2-q13 (70-75%), maternal uniparental disomy (matUPD) (25-30%), imprinting defects (~1%), and imprinting center deletions (10-15% of those with an imprinting defect) (Beygo et al. 2019).
Angelman syndrome (AS) is characterized by severe developmental delay, intellectual disability, movement or balance abnormalities, behavioral abnormalities, and severe limitations in speech and language (Beygo et al. 2019). Most cases are caused by the loss of maternally expressed genes on chromosome 15q11.2-q13. This loss of imprinting may be caused by a large deletion of the maternal 15q11-q13 (75%), paternal uniparental disomy (patUPD) (1-2%), imprinting defects (3%), imprinting center deletions (10-15% of patients with imprinting defects) or pathogenic variants in UBE3A, with the remainder of cases with no identifiable molecular abnormality (Beygo et al. 2019).
Testing for Prader-Willi/ Angelman Syndrome by methylation-sensitive multiplex ligation-dependent probe analysis (MS-MLPA) will simultaneously detect deletions, duplications and copy number neutral changes (ie uniparental disomy, UPD); additionally, methylation status will elucidate parent of origin for all events. Sequencing for UBE3A may be ordered as a separate test for Angelman syndrome if results for MS-MLPA are normal (KDL test code 1240).
Reasons for Referral:
Diagnostic Testing
Methodology:
DNA methylation and deletion-duplication based analysis of the promoter region of the SNRPN gene. This is performed by MS-MLPA analysis of undigested and digested genomic DNA.
Specimen Requirements:
Blood: EDTA or ACD (Solution A or B):
- Adult: 5 mL
- Child: 5 mL
- Infant: 2-3 mL
Saliva: 2 ORAgene Saliva Kits (OGR-500) used according to manufacturer instructions. Please contact KDL Client Services for a Saliva Collection Kit for patients that cannot provide a blood sample.
Assisted Saliva: 4 ORAgene Assisted Saliva Kits (OGR-575) used according to manufacturer instructions. Please contact KDL Client Services for an Assisted Saliva Collection Kit for patients that cannot provide a blood sample.
Prenatal:
- Direct Amniotic Fluid (10-20mL)
- Direct CVS
- Direct POC
- Cultured Amniocytes (2-T25 flasks)
- Cultured CVS (2-T25 flasks)
- Cultured Fetal Tissue: Production of Conception (2-T25 flasks)
- Cord Blood (1-2mL)
DNA: 500ng at a minimum of 50-100ng/µL (DNA must be extracted in a CLIA-certified laboratory or a laboratory meeting equivalent requirements as determined by the CAP and/or CMS)
Notice Regarding Molecular Genetic Testing on Prenatal Specimens:
- Maternal cell rule-out testing will be performed on all prenatal specimens received. Please provide maternal blood (or saliva) in addition to the fetal specimen. Additional charges apply for the maternal cell rule-out test.
For routine testing of blood and saliva (or DNA extracted from these specimens), KDL does NOT accept samples from patients within two (2) weeks of a packed cell/platelet transfusion or within four (4) weeks of a whole blood transfusion. For extraordinary circumstances, where testing must be performed within of the above windows, please contact the laboratory.
A REQUISITION FORM MUST ACCOMPANY ALL SAMPLES. Please include detailed clinical information, including ethnicity, clinical history, and family history.
Test Performed (Days):
Weekly
Turn Around Time:
14-21 days
Shipment Sensitivity Requirements:
- Package and ship specimen to remain cold, but not frozen.
- Ship via overnight express, using the FedEx priority overnight label provided.
- Contact Client Services for shipping kits and instructions at (855) 535-1522.
References:
- Duis J, van Wattum PJ, Scheimann A, et al. A multidisciplinary approach to the clinical management of Prader-Willi syndrome. Mol Genet Genomic Med. 2019;7(3):e514. PMID: 30697974.
- Miller JL, Lynn CH, Driscoll DC, et al. Nutritional phases in Prader-Willi syndrome. Am J Med Genet A. 2011;155A(5):1040-1049. PMID: 21465655.
- Beygo J, Buiting K, Ramsden SC, Ellis R, Clayton-Smith J, Kanber D. Update of the EMQN/ACGS best practice guidelines for molecular analysis of Prader-Willi and Angelman syndromes. Eur J Hum Genet. 2019;27(9):1326-1340. PMID: 31235867.
Additional Info:
The initial genetic evaluation to rule out PWS/AS should include chromosomal microarray analysis to detect any chromosome abnormalities that may have phenotypic similarities with PWS/AS, as well as methylation-sensitive MLPA to identify deletions, duplications, and methylation defects. Please use KDL test code 6500 for chromosomal microarray testing.
Beta-propeller protein-associated neurodegeneration (BPAN) a childhood disorder characterized by seizures, developmental delay/intellectual disability, movement disorder and behavioral abnormalities has overlapping features with Angelman syndrome. This X-linked disorder is associated with pathogenic variants in WDR45. Therefore, molecular testing for WDR45 may be indicated following negative methylation and sequencing testing for Angelman syndrome.