Prion Diseases and their Prpsc-Based Molecular Diagnostics

Prion diseases, also known as Transmissible Spongiform Encephalopathies (TSEs), are fatal neurodegenerative disorders with characteristic sponge-like microscopic appearance in the infected brain. They are caused by a protein-only particle consisting of an abnormal isoform (PrPSc) of the normal ubiquitous cellular prion protein PrPc. Prion diseases affect both human and animals, and can cause interspecies Corbière. In humans, there are six different phonotypes of prion diseases, including kuru disease, Creutzfeldt-Jakob disease (CJD), GerstmannSträussler-Scheinker (GSS) syndrome, Fatal Familial Insomnia (FFI), variant Creutzfeldt-Jakob disease (vCJD) and variably protease sensitive prionopathy (VPSPr). There are five well-studied prion diseases in herbivorous animals and carnivorous animals, including scrapie, Bovine Spongiform Encephalopathy (BSE), Chronic Wasting Disease (CWD), Transmissible Mink Encephalopathy (TME), and Feline Spongiform Encephalopathy (FSE). As the pathogen of the diseases, PrPSc accumulates in tissues and body fluids of the affected individuals, and serves as the most reliable marker for diagnosis of prion diseases. The bioassay, immunoblotting, immunohistochemistry (IHC), and enzyme-linked immunosorbent assay (ELISA) tests have been used in prion disease diagnosis and surveillance, but they are not sufficient for the preclinical diagnosis. The newly improved in vitro PrPSc amplification methods, such as protein misfolding cyclic amplification (PMCA), amyloid seeding assay (ASA), and real-time quaking-induced conversion (RT-QUIC), showed greatly increased sensitivity. Recently, RT-QUIC and PMCA were applied to noninvasive tests targeting PrPSc in urine or nasal swab, making early diagnosis and surveillance of prion diseases become more practical.