The control cells (FMR1 unmethylated, 8330-iPS8 and 131-iPS3) had extensive long and highly branched processes, while the FXS iPSC-derived cells (FMR1 methylated; 848-iPS1, 848-iPS3, and 131-iPS1) exhibited fewer and much shorter processes (Fig. 5 and Fig. S1). Here, FMR1 is linked to fragile X syndrome.