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Prion diseases are a group of rare, neurodegenerative brain disorders.

In humans, the best known of the prion diseases is Creutzfeldt-Jakob Disease (CJD).

CJD reportedly affects around 1 to 1.4 people per million per population per year.
In the United States, this translates to approximately 500 new cases per year.

There are three forms of CJD:

Sporadic CJD (sCJD) occurs for no apparent reason and accounts for 85% of the cases.

Cause: Unknown

Distinguishing Features: Affects mainly people over the age of 60. Common symptoms include ataxia and dementia. Short course. Upon tissue examination there is spongiform change, but plaques are rarely present.

Sporadic Fatal Insomnia (sFI) is an extremely rare form of Sporadic CJD representing less than 1% of all cases. sFI has clinical and histopathologic features indistinguishable from those of Fatal Familial Insomnia (FFI), but does not have the mutation on the prion gene that characterizes FFI.

Genetic Prion Disease mutations are inherited in an autosomal dominant pattern - if one parent carries the mutation there is a 50-50 chance for each child to inherit the gene.

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Acquired cases represent less than 1% of cases in the U.S.

Form: Iatrogenic CJD (iCJD)

Cause: Contamination through brain surgery, corneal transplant, dura mater graft, or growth hormone.

Distinguishing Features: Age at onset depends on the age at exposure and on the incubation time. Clinical and pathological features are often indistinguishable from sCJD. Growth hormone cases show plaques.

Form: Variant CJD (vCJD)

Cause: Exposure to BSE through consumption of infected beef or blood or plasma transfusion.

Distinguishing Features: With exposure to BSE, younger onset and longer duration than sporadic CJD. Psychiatric symptoms are often seen at disease presentation. Distinctive “daisy” plaques upon tissue examination. For blood or plasma transfusion, age at onset depends on the time of exposure.

Variant CJD has been linked to ingestion of beef tainted with BSE (bovine spongiform encephalopathy).

In animals, prion diseases first came to public attention in the mid-1980s in the form of the BSE epidemic in the United Kingdom. BSE (bovine spongiform encephalopathy) is a prion disease in cattle. Tissue from infected animals may have contaminated cattle feed, leading to the silent spread of the BSE epidemic. There is also a theory that BSE came from feed contaminated with scrapie, the long-established sheep prion disease. Inevitably, concern over whether BSE could pass to humans mounted.