[Fatal familiar insomnia: clinical, neurophysiological and histopathological study of two cases]

Family prion diseases are caused by mutations in the gene coding the prion protein (PrP), originating an altered isoform called prion. One of the most uncommon is the fatal familial insomnia (FFI), an entity characterized by sleep disorders and that is associated to a mutation in codon 178.

We have studied two male patients, aged 43 and 49 years respectively, from the same family.

The most significant symptoms were sleep disorders with agitation, fractionated sleep, snoring and daytime sleepiness. The evolution was brief, the patient dying at a few months of the clinical debut. Sleep registries showed destructuration with total loss of the normal cycle of the phases and great decrease of the sleep spindles and K complexes in both cases. The polygraphy showed tachycardia and apnea pauses. In the molecular study, a mutation in the codon 178 was detected, both being methionine/methionine homozygotes at position 129. The most outstanding neuropathological abnormalities were located in the thalamus with gliosis and neuronal loss of anterior and dorsomedial ventral nuclei and also intense neuronal loss in olive of the first case.

This study describes two new cases of FFI with genotype D178N-129M and short course classical phenotype. The polysomnography is essential in the diagnostic strategy of this disease whose neuropathological substrate is the thalamic alterations and of the inferior olive. Molecular biology permits an exact diagnosis of FFI although there is still controversy on the phenotypal variability and physiopathogenic mechanisms.