A deadly prion disease: fatal familial insomnia.

Fatal familial insomnia (FFI) is an inherited disease caused by a mutation in the protein prion gene. Symptoms of FFI closely resemble those of familial Creutzfeldt-Jakob disease, making genetic testing and histological examination of brain tissue the only means to determine a definitive diagnosis. The disease is rare--approximately 60 cases have been detected worldwide since 1986.