Gerstmann-Straussler-Scheinker syndrome (MONDO_0007656, a Monarch Disease Ontology entry) is a very rare and fatal disorder of spongiform encephalopathy usually caused by mutations of the prion protein (PRNP) gene. It is characterized by the accumulation of amyloid in the brain. Signs and symptoms include lack of motor coordination, unsteady gait, and difficulty walking. As the disease progresses, patients develop speech difficulties and dementia. Also known as: Gerstmann-Straussler-Scheinker disease, prion dementia, subacute spongiform encephalopathy, Gerstmann-Straussler type.