Activates CDC42, a member of the Ras-like family of Rho- and Rac proteins, by exchanging bound GDP for free GTP. Plays a role in regulating the actin cytoskeleton and cell shape. Interacts with DBNL/ABP1 and CTTN. May interact with CCPG1 (By similarity). Binds CDC42. Associated with membrane ruffles and lamellipodia. Expressed in fetal heart, brain, lung, kidney and placenta. Less expressed in liver; adult heart, brain, lung, pancreas and skeletal muscle. The DH domain is involved in interaction with CCPG1. The disease is caused by variants affecting the gene represented in this entry.