Missense mutation of Fmr1 results in impaired AMPAR-mediated plasticity and socio-cognitive deficits in mice

Fragile X syndrome (FXS) is the most frequent form of inherited intellectual disability and the best-described monogenic cause of autism. CGG-repeat expansion in the FMR1 gene leads to FMR1 silencing, loss-of-expression of the Fragile X Mental Retardation Protein (FMRP), and is a common cause of FXS. Missense mutations in the FMR1 gene were also identified in FXS patients, including the recurrent FMRP-R138Q mutation. To investigate the mechanisms underlying FXS caused by this mutation, we generated a knock-in mouse model ( Fmr1 R138Q ) expressing the FMRP-R138Q protein. We demonstrate that, in the hippocampus of the Fmr1 R138Q mice, neurons show an increased spine density associated with synaptic ultrastructural defects and increased AMPA receptor-surface expression. Combining biochemical assays, high-resolution imaging, electrophysiological recordings, and behavioural testing, we also show that the R138Q mutation results in impaired hippocampal long-term potentiation and socio-cognitive deficits in mice. These findings reveal the functional impact of the FMRP-R138Q mutation in a mouse model of FXS. The R138Q mutation in the Fragile X Mental Retardation 1 ( FMR1 ) gene has been associated with Fragile X syndrome (FXS). Here, the authors present a Fmr1 R138Q Knock-In mouse model and show that R138Q mutation results in impaired long-term potentiation and socio-cognitive performance in these mice.