Angelman syndrome (AS), also known as pleasant puppet syndrome, like PWS, can be caused by deletion of chromosomal fragment 15q11-q13. AS occurs due to maternal overexpression of the 15q11-q13 gene, and its genetic pathology includes maternal 15q11-q13 microdeletions, paternal UPD, imprinted genes, and UBE3A mutations. The UBE3A gene is maternal in origin and is specifically expressed in brain tissue. 15%-20% of AS patients are associated with their mutations, which are heterogeneous and mostly de novo. Clinical features: postnatal microcephaly, short head dysmorphism, severe mental retardation, speech disorders, ataxic gait, arm and elbow lift, tremor, seizures, hyperactivity, mandibular protrusion, salivation, open mouth and tongue, and unconscious laughter, as well as an EEG characterized by large amplitude slow-peaked waves are the main clinical features. Patients are usually normal at birth but soon develop severe developmental delays. iQ is at a severely impaired level. In early childhood, there is a lack of language development, unconscious laughter with joyful gestures, and often laughter when encountering mental or physical stimuli, hence the name “joyful puppet”. Treatment is mainly symptomatic. Special behavioral and linguistic education and corresponding psychological treatment in a good environment can reduce the patient’s symptoms. For abnormal behavior, ataxia and possible seizures, appropriate protective measures are taken by giving specific living environment and living supplies, such as special chairs, immobilizers and bedrooms. Medication is usually required for seizures, commonly used are clonidine and phenobarbital. Prevention: 1. In cases with a family history, routine amniotic fluid or chorionic villus cell cultures are done and relevant genetic diagnostic tests are done. 2. Do prenatal diagnosis and genetic counseling for pregnant women of advanced age and carriers of hidden chromosomal structural aberrations in the family.