AP1S2 and congenital hydrocephalus: Thereinto, X-linked hydrocephalus comprises about 5–15% of genetic-related congenital hydrocephalus (Haverkamp et al., 1999; Zhang et al., 2006; Adle-Biassette et al., 2013), and bona fide mutations have been described in four genes, that is, L1 cell adhesion molecule (L1CAM), sigma 2 subunit of the adapter protein 1 complex (AP1S2), multiple PDZ domain proteins (MPDZ), and coiled-coil domain-containing protein 88c (CCDC88C) (Tarpey et al., 2006; Al-Dosari et al., 2013; Shaheen et al., 2017; Yang et al., 2019; Etchegaray et al., 2020; Marguet et al., 2021; Wang et al., 2021).