Loss-of-function mutations in the maternal UBE3A copy or de novo deletions of chromosomal region 15q11-q13, in which UBE3A resides, cause the severe neurodevelopmental disorder Angelman syndrome (AS), characterized by abnormal motor development, lack of speech, seizures, and a happy demeanor (Kishino et al., 1997; Matsuura et al., 1997). The gene discussed is UBE3A; the disease is neurodevelopmental disorder.