UBE3A and microcephaly: Individuals with a UBE3A mutations have a milder AS phenotype with severe developmental delay, absence of speech, inappropriate laughter and EEG abnormalities as the most consistent findings and ataxia, epilepsy and microcephaly can present as mild or even absent [53, 54], suggesting that loss of UBE3A expression in neurons alone is not enough to recapitulate all aspects of the AS phenotype.