Small ubiquitin-like modifier (SUMO), also known as SUMO homologue and SMT3, is a member of the superfamily of ubiquitin-like polypeptides that become covalently attached to various intracellular target proteins as a way to alter their function, location, and/or half-life. Small ubiquitin-like modifiers include SUMO1, SUMO2, SUMO3, and SUMO4. Except for SUMO4, all other SUMOs are ubiquitously expressed, including in the brain. In human, SUMO2 and SUMO3 are two highly homologous proteins, collectively called SUMO2/3. Several studies suggest that SUMO3 are associated with pathogenesis in several neurological diseases, including Alzheimer's disease, Parkinson's disease, and cerebral ischemia/stroke.