FMR1 and fragile X syndrome: The FXS disorder is caused by the loss of Fragile X Mental Retardation Protein (FMRP) that triggers alterations in glial cells, as demonstrated in FMRP knockout (KO) mice models where decreased hippocampal and neocortical circuitry synapses associated with astrocytes were observed (Simhal et al., 2019).