Children with Angelman syndrome are generally late to develop and speak very little but have good linguistic comprehension. They have a protruding lower jaw or tongue. They laugh often, hold their arms as if they were a marionette, and flap them around, which gave the syndrome its initial name, "happy puppet syndrome".
The gene of Angelman syndrome (part of the ubiquitin pathway) is expressed only on the maternal chromosome. The first seven genes in the segment, whose deletion causes Prader-Willi syndrome, are expressed only on the paternal chromosome. It is thus possible for a man with Angelman syndrome to pass the mutation to his daughter, who has Prader-Willi syndrome. This is the first known instance of imprinting in humans.
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