Angelman syndrome (AS) is a neurodevelopmental 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.
AS is named after a British pediatrician, Harry Angelman, who first described the syndrome in 1965. An older, alternative term for AS, “happy puppet syndrome”, is generally considered pejorative and stigmatizing so it is no longer the accepted term. People with AS are sometimes referred to as “angels”, both because of the syndrome’s name and because of their youthful, happy appearance.