Prion Diseases Flashcards
What is the infectious agent for scrapie (CJD)?
PrPsc which is associated with the characteristic intracellular fibrils seen in diseased tissue.
What are the characteristics of prions?
Small size
Lack of a nucleic acid genome
Extreme resistance to heat, disinfectants, and irradiation
Slow replication-typically diseases have a long incubation period and appear later in life.
Cannot be cultured in vitro.
Do not elicit immune or inflammatory responses.
How did this protein come about?
Derived from naturally occurring PrPc which is found on the surface of nerve cells and coded by a single copy gene of unknown function (located on chromosome 20).
What are the differences between the two proteins?
PrPsc is globular (beta-pleated sheet) and enzyme resistant, PrPc is linear (alpha-helical sheet) and enzyme susceptible.
How are humans susceptible to vCJD?
Homozygosity for methionine at codon 129 of the prion-protein gene is a major determinant of susceptibility to sporadic, iatrogenic and vCJD.
How is vCJD transmitted?
Eating contaminated beef products.
How are prion diseases normally transmitted?
Mutations, eating contaminated food, use of contaminated medical products (blood, hormone extracts, transplants), the introduction of prions from contaminated instruments during surgical procedures as prions bind to metal surfaces and possible mother-foetus transmission during pregnancy.
How was kuru transmitted?
Eating dead human brains in funeral rites.
How did BSE (bovine spongiform encephalopathies) come about?
Sheep infected with scrapie passed onto cattle forming BSE which was then eaten by humans. In these cases, prions survive digestion and are taken up across the intestinal mucosa. They are then carried in lymphoid cells, eventually being transferred into neural tissues and enter the CNS.
Why is BSE said to come from scrapie infected sheep?
They were caused by the same prion strain.
What’s the difference between CJD and nvCJD?
The incubation period is shorter and the new form causes disease in younger individuals (14 years and upwards).
Where did kuru originate from?
Papua New Guinea.
Analysis of the prion protein gene (PRNP) showed that most patients with kuru were heterozygous at codon 129. True or False?
True.
How can you diagnose prion diseases?
They cannot be diagnosed by conventional means such as through culturing but clinical appearances usually indicate the probable occurrence of prion disease. Tonsillar tissue is a good source of PrPsc and prions can be identified by immunoblotting or immunohistochemistry.
Name four human prion diseases.
Creutzfeldt-Jakob disease.
Gerstmann-straussler-scheinker disease.
Fatal familial insomnia
Kuru
