Ans. d (SSPE). (Ref. Robbin, Pathology, 7th ed., 346)PRIONS# Pruissner was first person to describe the prion proteins (1997) & he got noble prize for the same.# Prion diseases are the transmissible spongiform encephalopathies, which include:- Creutzfeld Jakob disease- Gerstmann-Straussler-Seheinker syndrome- Fatal familial insomnia- Kuru- Mad cow disease# Prions are infectious proteins that cause degeneration of the CNS.# These infectious agents are protein in nature, devoid of DNA and RNA# Unusually resistant to physical and chemical agents like heat, irradiation, and formalin.- Prion diseases are disorders of protein conformation, the most common of which in humans is called Creutzfeldt- Jakob disease (CJD).- CJD typically presents with dementia and myoclonus, is relentlessly progressive, and generally causes death within a year of onset.- Most CJD patients are between 50 and 75 years of age.# Four new concepts have emerged from studies of prions:- Prions are the only known infectious pathogens that are devoid of nucleic acid (No RNA or DNA).- Prion diseases may manifest as infectious, genetic, and sporadic disorders (no other group of illnesses with a single etiology presents with such a wide spectrum of clinical manifestations).- Prion diseases result from the accumulation of PrPSc, the conformation of which differs from that of its precursor PrPC.Glossary of prion terminologyTermCommentsPrionProteinaceous /nfectious particle that lacks nucleic acid. Prions are composed largely, if not entirely, of PrPSc molecules.PrPScDisease-causing isoform of the prion protein. This protein is the only identifiable macromolecule in purified preparations of scrapie prions.PrPCCellular isoform of the prion protein. PrPC is the precursor of PrPSc.PrP 27-30A fragment of PrPSc, generated by truncation of the NH2-terminus by limited digestion with proteinase K. PrP 27-30 retains prion infectivity and polymerizes into amyloid.PRNPPrP gene located on human chromosome 20.Prion rodAn aggregate of prions composed largely of PrP 27-30 molecules.Created by detergent extraction and limited proteolysis of PrPSc. Morphologically and histochemicaily indistinguishable from many amyloids.PrP amyloidAmyloid containing PrP in the brains of animals or humans with prion disease; often accumulates as plaques.