MAGEL2 and Prader-Willi-like syndrome: Schaaf-Yang syndrome (SYS) was originally considered Prader-Willi-like syndrome because it is caused by a nonsense frame shift mutation in the maternally imprinted and paternally expressed MAGEL2 gene located in the Prader-Willi critical region 15q11–15q13, also called the MAGEL2 loss of function [22,49].