Alteration of the serotonergic nervous system in fatal familial insomnia

Fatal familial insomnia (FFI) is a unique hereditary prion disease with cha racteristic disturbances of sleep. We studied the serotonergic system in 8 FFI-affected subjects by immunohistochemistry for the serotonin-synthesizin g enzyme, tryptophan hydroxylase (TH), Quantification of neurons in median raphe nuclei showed no total neuronal loss in FFI but a substantial increas e of TH+ neurons (similar to 62%) in FFI subjects compared with controls. O ur data indicate an alteration of the serotonergic system that might repres ent the functional substrate of some typical symptoms of FFI.