MAGEL2 and Schaaf-Yang syndrome: The neurodevelopmental disorders (NDDs) Schaaf-Yang syndrome [SYS; Online Mendelian Inheritance in Man (OMIM) #615547], Chitayat-Hall syndrome and Opitz trigonocephaly C syndrome (OMIM #211750) share overlapping clinical features that have been attributed to commonly shared loss-of-function truncating mutations in the imprinted gene MAGEL2.