Overview of Prion Diseases
(Transmissible Spongiform Encephalopathies)
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Prion diseases are progressive, fatal, and untreatable degenerative brain disorders. They include

Creutzfeldt-Jakob disease (CJD), the prototypic example

Gerstmann-Sträussler-Scheinker disease (GSS)

Fatal insomnia (FI)

Variant CJD (vCJD)

Kuru

Prion diseases usually occur sporadically, with a worldwide annual incidence of about 1/1 million.

Prion diseases result from misfolding of a normal cell-surface brain protein called prion protein (PrP), whose exact function is unknown. Misfolded prion proteins (or prions) induce previously normal PrP to misfold; they are markedly resistant to degradation (similar to β-amyloid, which they resemble), resulting in slow but inexorable intracellular accumulation and neuronal cell death. Accompanying pathologic changes include gliosis and characteristic histologic vacuolar (spongiform) changes, resulting in dementia and other neurologic deficits. Symptoms and signs develop months to years after exposure.

Prion diseases can be caused by spontaneous or hereditary defects of the PrP gene, contained in the short arm of chromosome 20. Some defects cause familial CJD, some cause GSS, and others cause FI. Small abnormalities in particular codons may determine the predominant symptoms and rate of disease progression.

Prion diseases can also be transmitted by infected tissue. Cannibalism caused the spread of kuru in New Guinea, and prions can be transmitted via organ transplants and rarely by blood transfusion. Prion diseases can be transmitted between species via the food chain (eg, in vCJD). Prion diseases occur in mink, elk, deer, domestic sheep and cattle, and other mammals. In several western US states and Canada, chronic wasting disease of elk and deer, a prion disease, is a concern; whether this disease can be transmitted to people who hunt, butcher, or eat affected animals is unknown.

Prion diseases should be considered in all patients with dementia, especially if it progresses rapidly.

Treatment is symptomatic. Prions resist standard disinfection techniques and pose risks to surgeons, pathologists, and technicians who handle contaminated tissues and instruments.