Given that many XLID genes are neuronally enriched (Devys et al., 1993; Budreck and Scheiffele, 2007; Toya et al., 2023; Rusconi et al., 2008; Guarnieri et al., 2017; Murphy et al., 2006; Bienvenu et al., 2002), an a priori hypothesis is that ZDHHC9 acts in neurons. Here, ZDHHC9 is linked to cask-related x-linked intellectual disability.