Progressive fatal processes that have variable clinical manifestations with a similar noninflammatory pathology and pathogenesis. These diseases are associated and probably caused by the accumulation of an abnormal form of the prion protein. They include kuru (a cerebellar degeneration among the Fore tribesmen of New Guinea), fatal familial insomnia (a rare autosomal dominantly inherited disease characterized by insomnia and dysautonomia), sporadic fatal insomnia (a non-inherited disease similar to fatal familial insomnia), and thalamic dementia (probably a form of fatal familial insomnia).