AP1S2 and syndromic X-linked intellectual disability 5: Since the AP1S2 gene mutation was identified as the cause of PGS in 2006, only nine AP1S2 mutations have been found in literatures, including eight point mutations and a microdeletion (Bassani et al., 2013; Carpenter, Brown, Qu, & Keenan, 1999; Kongsvik et al., 2002; Pettigrew et al., 1991; Tzschach et al., 2015).