Angelman syndrome: An important genetic syndrome characterized by severe motor and intellectual retardation, microcephaly (abnormally small head), ataxia, frequent jerky limb movements and flapping of the arms and hands, hypotonia (floppiness), hyperactivity, seizures, absence of speech, frequent smiling and outbursts of laughter, and an unusual facies (facial appearance) characterized by macrostomia (large mouth), a large jaw and open-mouthed expression, and a great propensity for protruding the tongue (tongue thrusting). The name Angelman syndrome is now preferred because the old term "happy puppet syndrome" may appear derisive to the child's family.
Angelman syndrome is due in most cases to a chromosome deletion involving loss of material from chromosome region 15q11-q13. The loss is consistently of the contribution of chromosome region 15q11-q13 from the mother. This loss is due to a new deletion in most cases.
Deletion of chromosome region 15q11-q13 causes both Angelman syndrome and a totally different disorder called Prader-Willi syndrome. However, while the deleted chromosome is of maternal origin in Angelman syndrome, it is the paternal chromosome that is partially deleted in the Prader-Willi syndrome.
There are rare families with more than one child with Angelman syndrome. The mode of inheritance in these families is autosomal dominant modified by imprinting.