Usually a sporadic disorder, it is characterised by profound intellectual deficiency, a striking puppet-like ataxic gait and facial features, paroxysmal laughter and seizures. These features are responsible for its alternative designation as happy puppet syndrome.
An interstitial deletion at chromosome band 15q12 was identified and can be detected in a large proportion of cases and the defect is linked to the gaba receptor gene. Chromosome haplotyping will always reveal the deletion to be carried on the maternally-derived chromosome 15, alternatively, angelman syndrome can be caused by uniparental disomy for the paternal chromosome 15. In both cases, this suggests that angelman syndrome results from loss or disruption of a gene (or genes) on chromosome 15 that must be inherited through the maternal gamete in order to be properly expressed.
The opposite phenomenon is seen in the prader-willi syndrome, in which a deletion of a nearby region on chromosome 15q is found on the paternally-derived chromosome, or there can be uniparental disomy for the maternally derived chromosome. Thus, both disorders seem to represent examples of genes which are subject to imprinting.