Also, the Snrpn-Ube3a locus is involved in the classic sister imprinting disorders Prader-Willi syndrome (OMIM: 176270) and Angelman syndrome (OMIM: 105830), both of which display developmental delay and deficits in cognitive function (Knoll et al., 1989; Wagstaff et al., 1992). This evidence concerns the gene UBE3A and Prader-Willi syndrome.