UBE3A and Prader-Willi syndrome: Moreover, in this cohort, 83.3% of PWS were caused by paternal microdeletion, 16.7% by UPD(15)mat; while 85.7% of AS were caused by maternal microdeletion, 7.1% by UPD(15)pat, and 7.1% by UBE3A gene mutation.