ARHGEF9 and epilepsy: In recent years, the importance of collybistin, encoded by Cdc42 Guanine Nucleotide Exchange Factor 9 (ARHGEF9), to functional inhibitory synapses has become clear with the discovery of multiple patients with ARHGEF9 mutations that present with disease syndromes including epilepsy (Shimojima et al., 2011; George et al., 2021; Hines et al., 2022).