Sleep disorders in prion diseases

Prion diseases are a group of encephalopathies with neurodegenerative changes caused by an altered protein named prion whose characteristic datum is transmissibility. In most cases they occur in a sporadic form although a group of them are familial associated with mutations in the gene of the prion protein. Genetic polymorphism seems to determine the different family variants. One of the most enigmatic and unusual is Fatal Familial Insomnia (FFI), a hereditary disorder characterised by loss of physiological sleep with oneiric stupor, autonomic and motor hyperactivity, and motor anomalies. The polysomnography of this entity reflects an inability to produce the physiological pattern of NREM and REM sleep, as well as hormonal and vegetative circadian fluctuations; the transition from wakefulness to sleep is markedly altered with the early disappearance sleep spindles. The hypothesis of the origin of these disorders is thalamic neuronal loss, especially in the anterior and dorsomedial nuclei, described in the neuropathology of these patients; besides PET reveals hypofunction of thalamic nuclei, centres responsible for controlling wakefulness-sleep. In Creutzfeldt-Jakob disease the wake-sleep disorders are not considered characteristic; nonetheless, frequent alterations have been found in the electroencephalographic registers of sleep. Besides thalamic neurodegeneration, there could be common etiopathogenic mechanisms in prion diseases in relation to the biological function of the prion protein.