Mild Angelman syndrome phenotype due to a mosaic methylation imprinting defect.

Angelman syndrome (AS) is a neurogenetic disorder causing severe to profound intellectual disability, absent or very limited speech and a high risk for seizures. AS is caused by a loss of function of the maternally-derived UBE3A allele due to one of several mechanisms including imprinting defects (ImpDs). We present a girl with AS due to a mosaic ImpD who has relatively high developmental function (VABS-II composite score of 76) and communication skills (as demonstrated in supplemental video links).