UBE3A and Angelman syndrome: Further, studies show that the inactivation of Ube3a-ATS by CRISPR/Cas9 editing at the level of DNA and RNA result in expression of sense Ube3a in the brain of Angelman syndrome mice by gene therapy approach with adeno-associated virus (AAV) to deliver Cas9 nuclease as well as guide RNA constructs (Wolter et al., 2020; Schmid et al., 2021).