priions

Prions (often misspelled as priions) are infectious agents composed solely of misfolded protein, specifically a conformer of the normal cellular prion protein (PrP^C). They lack nucleic acids and can propagate by inducing misfolding of normally folded PrP in the host. The term prion was coined by Stanley B. Prusiner in 1982.

In health, PrP^C is a glycosylphosphatidylinositol-anchored cell-surface protein abundant in nervous tissue. PrP^Sc, the disease-causing form, has a higher beta-sheet content and forms aggregates resistant to proteases. Conversion of PrP^C to PrP^Sc is thought to occur by templated misfolding, leading to neurodegeneration and spongiform changes.

Prions cause transmissible spongiform encephalopathies (TSEs) in humans and animals. In humans, sporadic CJD is most common; familial cases arise from PRNP mutations; iatrogenic cases have occurred via contaminated medical procedures. A human prion disease, variant CJD, emerged in the late 20th century linked to exposure to bovine spongiform encephalopathy (BSE).

Diagnosing prion diseases relies on clinical features plus laboratory tests. Magnetic resonance imaging, electroencephalography, and CSF biomarkers such as 14-3-3 protein support diagnosis; real-time quaking-induced conversion (RT-QuIC) assays detect PrP^Sc seeding activity. Definitive confirmation requires neuropathological examination postmortem.

There is no cure or approved vaccine for prion diseases; treatment is supportive. Prions are remarkably resistant to conventional disinfection, making careful handling and specialized decontamination essential in medical and laboratory settings. Prevention focuses on surveillance, feed controls in livestock, and minimizing exposure in medical contexts.

Prions challenge traditional views of infectious agents by lacking nucleic acids and reproducing via protein misfolding. Research continues into mechanisms, diagnosis, and potential therapies, and prion biology informs broader questions about proteinopathies and neurodegenerative diseases.