FMR1 and fragile X syndrome: Levels of the GABA synthesizing enzyme, glutamic acid decarboxylase, have also been found to be affected in Fmr1 knockout (KO) Drosophila. Lastly, recent studies reveal changes in GABAergic signaling at both pre- and post-synaptic domains of inhibitory synapses in an FXS mouse model (Kramvis et al., 2020).