A rare inherited neurodegenerative disease caused by a mutation in the PRNP gene that leads to the accumulation of abnormal prion proteins in the brain.the disease is a type of prion disease similar to Creutzfeldt–Jakob disease, but with slower progression. GSS usually manifests itself in middle age with symptoms such as progressive ataxia, cognitive decline, myoclonus (muscle twitching), and sometimes mental changes. Over time, the disease leads to severe neurological disorders and death. There is no cure, therapy aims to relieve symptoms and provide supportive care.