This revision: 9th May 2013 .
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Angelman syndrome is a neuro-genetic disorder characterized by severe intellectual and developmental disability, sleep disturbance, seizures, jerky movements (especially hand-flapping), frequent laughter or smiling, and usually a happy demeanor.
AS is a classic example of genomic imprinting in that it is caused by deletion or inactivation of genes on the maternally inherited chromosome 15 while the paternal copy, which may be of normal sequence, is imprinted and therefore silenced.
The sister syndrome, Prader-Willi syndrome, is caused by a similar loss of paternally inherited genes and maternal imprinting.
People with AS are sometimes known as "angels", both because of the syndrome's name and because of their youthful, happy appearance.