Because it was first described by a British paediatrician called Doctor Harry Angelman, in 1965. It was previously sometimes known as happy puppet syndrome due to sufferers' jerky movements and generally happy appearance but this name is now considered pejorative.Also because of there happy youthful expression.ecause it was first described by a British paediatrician called Doctor Harry Angelman, in 1965. It was previously sometimes known as happy puppet syndrome due to sufferers' jerky movements and generally happy appearance but this name is now considered pejorative. Also because of there happy youthful expression.