icism, the assay was also performed using bisulfite- treated DNA from 2 AS patient samples known to be mosaic and a PWS patient sample with a putative tripli- cation of the SNRPN promoter region on the maternally

unknown. To determine the capability of HRM to detect mosaicism, the assay was also performed using bisulfitetreated DNA from 2 AS patient samples known to be mosaic and a PWS patient sample with a putative triplication of the SNRPN promoter region on the maternally derived chromosome 15 (as determined by semiquantitative MSP, fluorescence in situ hybridization, and microsatellite analysis). The 2 mosaic AS cases were classified as variant at a confidence percentage threshold of 80%, and the melting curve shapes could be clearly distinguished from the AS and normal control groups (Fig. 1). The PWS sample with a putative triplication at the SNRPN locus on the maternally methylated chromosome was also classified as variant at a confidence percentage threshold of 80% and showed a melting curve shape that clearly differed from the normal control and PWS groups (Fig. 1).