FMR1 and fragile X syndrome: While impaired functional maturation is consistent with impaired development of the dendritic arbor and synaptic protein expression, our findings contrast with reports of increased calcium conductance and hyperexcitability associated with FMRP loss in both rodent and human cell models of FXS (Contractor et al., 2015; Achuta et al., 2018; Danesi et al., 2018; Brighi et al., 2021).