Fatal familial insomnia (FFI), or familial selective thalamic degeneration with a mutation at codon 178 of the prion protein (PrP) gene, is a rapidly progressive autosomal dominant disease characterized by progressive insomnia, dysautonomia, and myoclonus.
The plaque type prion diseases showed a long clinical course without myoclonus and periodic synchronous discharges, and the major PrP accumulation sites were extracellular PrP plaques.