Fatal familial insomnia (FFI), a condition characterized by inability to sleep, 
dysautonomia, motor disturbances, and selective thalamic atrophy is a prion 
disease linked to a GAC----AAC mutation at codon 178 of the prion gene. These 
data were obtained from one kindred. We now report a second kindred affected by 
FFI and carrying the same mutation. The finding of the same disease phenotype 
and genotype in a second family further validates FFI as a distinct disease 
entity and a phenotype of the GAC----AAC mutation at codon 178 of the prion 
gene.