UBE3A and Angelman syndrome: The UBE3A gene exhibits paternal-specific imprinting in the neuronal tissue and the loss of function of maternally inherited UBE3A results in Angelman syndrome (AS), a neurodevelopmental disorder typically characterized by severe delay in developmental milestones, intellectual disability, lack of speech and epilepsy along with several other accompanying features particularly excessive laughter and sleep disturbances (Albrecht et al., 1997; Kishino et al., 1997; Matsuura et al., 1997; Fang et al., 1999; Yamasaki et al., 2003; Williams et al., 2010).