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.