FXR1 and fragile X syndrome: The interaction of FMRP N-tat with both FXR1 and FXR2 was observed in FXS iPSC-derived neurons in the present study; however, although FXR1 was found in tsA-201 FMR1 KO cells treated with FMRP N-tat it did not reach the SAINT score cutoff.