ARHGEF9 (Rho guanine nucleotide exchange factor 9), also known as PEM-2 homolog or Collybistin, is a 516 amino acid cytoplasmic protein. ARHGEF9 acts as a guanine nucleotide exchange factor for Cdc42 and promotes formation of Gephyrin clusters by directly interacting with Gephyrin. ARHGEF9 contains one DH (DBL-homology) domain, one PH domain and one SH3 domain. Defects in the gene encoding ARHGEF9 are a believed to be a cause for startle disease with epilepsy (STHEE), also known as hyperekplexia with epilepsy. This disease is a heterogenous neurological disorder characterized by muscular rigidity, particularly in the neonatal period, and a startle response to auditory or tactile stimuli.
