Molecular Genetics Prader-Willi / Angelman Syndrome Methylation and Deletion/Duplication

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 are caused by a loss of imprinting of genes on chromosome 15q11-q13. This loss of imprinting may be caused by a large deletion of the paternal 15q11-q13 (75-80%), maternal uniparental disomy (matUPD) (20-25%), imprinting defects (~1%), and imprinting center deletions (10-15% of those with an imprinting defect) (Ramsden et al., 2010).

Angelman syndrome is characterized by severe mental retardation, movement or balance abnormalities, behavioral abnormalities, and severe limitations in speech and language.  Most cases are caused by a loss of imprinting of genes on chromosome 15q11-q13.  This loss of imprinting may be caused by a large deletion of the maternal 15q11-q13 (70-75%), paternal uniparental disomy (patUPD) (3-7%), imprinting defects (2-3%), and imprinting center deletions (10-15% of patients with imprinting defects) (Ramsden et al., 2010).  Additionally, mutations of UBE3A cause approximately 10% of Angelman Syndrome cases (Ramsden et al., 2010).

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.

Reasons for Referral:
Diagnostic Testing

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.

Blood:  EDTA or ACD (Solution A or B):

• Adult: 5 mL
• Child: 5 mL
• Infant: 2-3 mL

Saliva: 1 ORAgene Saliva Kit (OGR-500)

Prenatal:

• Direct Amniotic Fluid (10-20mL)
• Direct CVS
• Cultured Amnio or CVS (2-T25 flasks)

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 CVS or Amniotic Fluid Specimens:

• Maternal cell rule-out testing will be performed on all prenatal specimens received.Please provide maternal blood in addition to the fetal specimen.Additional charges apply for the maternal cell rule-out test.
• All genetic testing performed on Direct CVS or Direct Amniotic Fluid specimens will be confirmed on cell cultures prepared by Knight Diagnostic Laboratories.Cell cultures will be prepared from the specimen received.Additional charges apply for confirmatory testing.

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

Weekly

14-21 days

• 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.

1. Ramsden et al. (2010) BMC Medical Genetics 11:70.