Prion is a type of abnormal protein that induces structural changes in normal homologous proteins, causing them to adopt a pathological state. They are not based on nucleic acids and primarily consist of the pathogenic form of PrP protein, PrP^Sc. Prions mainly accumulate in neural system cells, affecting neuronal functions and leading to a range of neurodegenerative diseases. The expression of the PrP protein gene, PRNP, is tightly regulated across different tissues, while mutations in the PRNP gene increase the risk of certain prion diseases.