In order to determine whether the p.R356Q mutation affected collybistin binding to PI3P, we performed pulldown assays (Figures 2A,B) using PI3P immobilized on agarose beads incubated with lysates of HEK293 cells transfected with either tagged wild-type collybistin (myc-CB3SH3-), the new mutant myc-CB3SH3-R356Q, a known human XLID mutant known to be deficient in PI3P binding (myc-CB3SH3-R290H; Papadopoulos et al., 2015) or an artificial phosphoinositide binding site mutant myc-CB3SH3-R356N/R357N (Reddy-Alla et al., 2010). This evidence concerns the gene ARHGEF9 and cask-related x-linked intellectual disability.