Methylation-specific multiplex ligation-dependent probe amplification and identification of deletion genetic subtypes in Prader-Willi syndrome.

Purpose: Prader-Willi syndrome (PWS) and Angelman syndrome (AS) are complex neurodevelopmental disorders caused by loss of expression of imprinted genes from the 15q11-q13 region depending on the parent of origin. Methylation-specific multiplex ligation-dependent probe amplification (MS-MLPA) kits from MRC-Holland (Amsterdam, The Netherlands) were used to detect PWS and AS deletion subtypes. We report our experience with two versions of the MS-MLPA-PWS/AS kit (original A1 and newer B1) in determining methylation status and deletion subtypes in individuals with PWS. Methods: MS-MLPA analysis was performed on DNA isolated from a large cohort of PWS subjects with the MS-MLPA-PWS/AS-A1 and -B1 probe sets. Results: Both MS-MLPA kits will identify deletions in the 15q11-q13 region but the original MS-MLPA-A1 kit has a higher density of probes at the telomeric end of the 15q11-q13 region, which is more useful for identifying individuals with atypical deletions. The newer B1 kit contains more probes in the imprinting center (IC) and adjoining small noncoding RNAs useful in identifying small microdeletions. Conclusion: The A1 kit identified the typical deletions and smaller atypical deletions, whereas the B1 kit was more informative for identifying microdeletions including the IC and SNORD116 regions. Both kits should be made available for accurate characterization of PWS/AS deletion subtypes as well as evaluating for IC and SNORD116 microdeletions.