Fatal familial insomnia (FFI) is an extremely rare autosomal dominant inherited prion disease of the brain. It is almost always caused by a mutation to the protein PrP^C, but can also develop spontaneously in patients with a non-inherited mutation variant called sporadic fatal insomnia (sFI). FFI has no known cure and involves progressively worsening insomnia, which leads to hallucinations, delirium, and confusional states like that of dementia. The average survival span for patients diagnosed with FFI after the onset of symptoms is 18 months.