DLG4 and fragile X syndrome: The reduction of PSD-95 and vGLUT1 protein expression observed in FXS- hiDFP-derived neurons corresponds to the lack of DLG4 and SLC17A7 gene expression in FXS- hiDFP-derived neurons compared to controls (Figure 6) and indicates that FXS- hiDFP-derived neurons exhibit impaired synaptic maturation.