Recent studies have found that loss-of-function RAB39B mutations are associated with various diseases including XLID, autistic spectrum disorder (ASD), and Parkinson’s disease (PD) (Supplementary Table 1; Giannandrea et al., 2010; Mata et al., 2015; Guldner et al., 2016; Lesage et al., 2016; Shi et al., 2016; Ciammola et al., 2017; Woodbury-Smith et al., 2017; Santoro et al., 2020). The gene discussed is RAB39B; the disease is cask-related x-linked intellectual disability.