Prionic diseases.

Prion diseases are neurodegenerative illnesses due to the accumulation of small infectious pathogens containing protein but apparently lacking nucleic acid, which have long incubation periods and progress inexorably once clinical symptoms appear. Prions are uniquely resistant to a number of normal decontaminating procedures. The prionopathies [Kuru, Creutzfeldt-Jakob disease (CJD) and its variants, Gerstmann-Sträussler-Scheinker (GSS) syndrome and fatal familial insomnia (FFI)] result from accumulation of abnormal isoforms of the prion protein in the brains of normal animals on both neuronal and non-neuronal cells. The accumulation of this protein or fragments of it in neurons leads to apoptosis and cell death. There is a strong link between mutations in the gene encoding the normal prion protein in humans (PRNP) - located on the short arm of chromosome 20 - and forms of prion disease with a familial predisposition (familial CJD, GSS, FFI). Clinically a prionopathy should be suspected in any case of a fast progressing dementia with ataxia, myoclonus, or in individuals with pathological insomnia associated with dysautonomia. Magnetic resonance imaging, identification of the 14-3-3 protein in the cerebrospinal fluid, tonsil biopsy and genetic studies have been used for in vivo diagnosis circumventing the need of brain biopsy. Histopathology, however, remains the only conclusive method to reach a confident diagnosis. Unfortunately, despite numerous treatment efforts, prionopathies remain short-lasting and fatal diseases.