FMR1 and fragile X syndrome: As cortical hyperexcitability is one of the hallmarks of FXS, and neuronal hyperexcitability has been reported both in slices and culture of Fmr1 KO mouse model8, we characterized, through confocal analysis of immunofluorescence signals and functional recordings of calcium dynamics, the development of the glutamatergic and the GABAergic systems in 2D cortical cultures differentiated from FMRP-WT and FMRP-KO hiPSCs.