AD: RhoA is decreased in human AD brains and mice overexpressing Swedish mutant APP, RhoA increased in degenerating neurites of Swedish Aβ mutant mice (Huesa et al., 2010); human neuroblastoma cells exposed to Aβ show enhanced activation of RhoA and diminished activation of Rac1 (Petratos et al., 2008)SCI: inhibition of Rho protects (Boato et al., 2010; Boomkamp et al., 2012)I/R: Rho is upregulated following stroke in humans (Brabeck et al., 2003) and mice (Trapp et al., 2001; Erdo et al., 2004). The gene discussed is RAC1; the disease is Alzheimer disease.