The protein encoded by this gene is a Rho-like GTPase that switches between the active (GTP-bound) state and inactive (GDP-bound) state to regulate CDC42 and other genes. Defects in this gene are a cause of startle disease with epilepsy (STHEE), also known as hyperekplexia with epilepsy. Three transcript variants encoding different isoforms have been found for this gene.[provided by RefSeq, Mar 2010],disease:Defects in ARHGEF9 are a cause of startle disease with epilepsy (STHEE) [MIM:300607], also known as hyperekplexia with epilepsy. Startle disease is a genetically heterogeneous neurologic disorder. STHE is characterized by muscular rigidity of central nervous system origin, particularly in the neonatal period, and by an exaggerated startle response to unexpected acoustic or tactile stimuli.,function:Acts as guanine nucleotide exchange factor (GEF) for CDC42. Promotes formation of GPHN clusters.,similarity:Contains 1 DH (DBL-homology) domain.,similarity:Contains 1 PH domain.,similarity:Contains 1 SH3 domain.,subunit:Interacts with GPHN.,tissue specificity:Detected in brain. Detected at low levels in heart.,
