Abstract for presentation at 11th International Congress of Human Genetics

Prader-Willi syndrome: Molecular analysis by real-time PCR

  • Ms Teresa Munce, Mater Pathology, Mater Health Services, South Brisbane AND School of Molecular and Microbial Sciences, University of Queensland, Australia
  • Mr Robert Simpson, School of Molecular and Microbial Sciences, University of Queensland, Australia
  • Marylou Doody, Mater Pathology, Australia
  • Dr David Cowley, Mater Pathology, Mater Health Services, South Brisbane, Australia
  • Prof Francis Bowling, Department of Paediatrics, Mater Children's Hospital, South Brisbane, Australia

    • Prader-Willi syndrome (PWS) is a contiguous gene syndrome caused by the loss of function of paternally derived/maternally imprinted genes within 15q11-q13. Molecular causes are reported to include interstitial deletions (70%), uniparental disomy (UPD) (20-25%), imprinting centre (IC) defects (5%) and chromosomal translocations (<1%). The standard diagnosis of PWS is based on clinical observations as well as genetic investigations involving DNA methylation studies and FISH analysis. The absence of a paternal methylation pattern within 15q11-q13 is sufficient for a diagnosis of PWS, while FISH analyses are used for the additional categorisation of patients as either deletion or non-deletion (presumed UPD). The limitations of these investigations are a) they do not determine the sizes of molecular deletions which have been reported to vary between patients, b) they do not detect individuals with defects in the PWS IC (promoter region and exon 1 of SNRPN) and c) FISH analyses have poor resolution.
    We have designed a real-time PCR assay with genomic DNA and sybr green I dye to map the size of molecular deletions in PWS patients. This includes those patients with micro-deletions in the PWS IC who were previously assumed to have UPD. Our real-time PCR assay relies on amplification of small (~100 bp) regions of targeted genes within 15q. By measuring the copy number of each region we have detected two deletion sizes in our PWS cohort. Our results are consistent with previous FISH and DNA methylation testing performed on each patient as part of their diagnostic investigations. This assay may also be useful for patients with the clinically distinct disorder Angelman syndrome (AS) who have a loss of paternally imprinted genes at the same genetic loci.

    Conference Organiser - ICMS Pty Ltd