SNRPN and Prader-Willi syndrome: On human chromosome 15q11–q13, paternally expressed genes, including MAGEL2, NDN, SNRPN, SNORD115 and SNORD116, are critical genes for Prader-Wiili syndrome (PWS) and form an 2-Mb imprinting cluster together with the AS gene UBE3A. Although not fully understood, it is generally believed that the PWS/AS region is regulated by a bipartite imprinting center composed of PWS-IC, which activates genes located in its proximity via looping and direct interacting with them, and AS-IC, which suppresses PWS-IC by transcription-mediated DNA methylation [4], [5].