Fatal familial insomnia (FFI) is a rare hereditary human prion disease with 
unique clinical features including progressive sleep impairment and autonomic 
dysfunction. The serotonergic system is considered to be involved in the 
regulation of the sleep-wake cycle. In this study we demonstrate a reduced 
availability of serotonin transporters of 57% and 73% respectively in a 
thalamus-hypothalamus region of two FFI patients examined with beta-CIT SPECT as 
compared to age-expected control values.