MAPK8IP3 and Intellectual disability: Intriguingly, AP-4 deficiency syndrome or AP-4-associated HSP, the human disorder arising from loss of AP-4 complex function, has several overlapping clinical presentations with the JIP3-linked neurodevelopmental disorder, including intellectual disability, hypoplasia of the corpus callosum, and developmental delays including problems with speech development (Ebrahimi-Fakhari et al., 1993; Iwasawa et al., 2019; Platzer et al., 2019).