A sleep that never comes: Prions and their role in fatal familial insomnia - a literature review.

Fatal Familial Insomnia (FFI) is a rare genetic prion disease that leads to progressive neurodegeneration and death. It is caused by the D178N mutation in the PRNP (Prion Protein Gene), combined with the presence of methionine at codon 129. The disease primarily affects the thalamus - a brain structure responsible for regulating the sleep-wake cycle. FFI develops in four stages, starting with initial insomnia and mood disturbances, progressing to a complete loss of the ability to sleep, and ultimately leading to the final stage of dementia and death within approximately 18 months from symptom onset. Prions - infectious proteins with an abnormal conformation - play a key role in the pathogenesis of FFI. The disease is associated with the misfolding of the normal prion protein (PrPC) into its pathogenic form (PrPSc), which accumulates in neural tissue, leading to neuronal death. Due to its rarity and nonspecific early symptoms, diagnosing FFI is challenging. Genetic testing, neuroimaging techniques such as PET and SPECT, which reveal characteristic thalamic hypometabolism and polysomnography, which identifies distinctive sleep architecture disturbances are crucial in the diagnostic process. Advancing noninvasive diagnostic methods and searching for potential therapies are key directions in FFI research. A deeper understanding of prion mechanisms, including how prion proteins misfold and transmit their aberrant conformation to other proteins, may contribute to the development of effective therapeutic strategies for this and other neurodegenerative diseases.