How and what causes spongiform encephalopathy?

 

Answer:

Transmissible spongiform encephalopathies are caused by prions, infectious proteins that appear to replicate by converting a normal cellular protein into copies of the prion. 

Causes

Viral hypothesis: This hypothesis postulates that an as of yet undiscovered infectious viral agent is the cause of the disease. Evidence for this hypothesis is as follows:

• Incubation time is comparable to a lentivirus
• Strain variation of different isolates of PrP^Sc
• An increasing titer of PrP^Sc as the disease progresses suggests a replicating agent.

Multi-component hypothesis: While not containing a nucleic acid genome, prions may be composed of more than just a protein. Purified PrP^C appears unable to convert to the infectious PrP^Sc form, unless other components are added, such as RNA and lipids. These other components, termed cofactors, may form part of the infectious prion, or they may serve as catalysts for the replication of a protein-only prion.

Genetics: Mutations in the PRNP gene cause prion disease. Familial forms of prion disease are caused by inherited mutations in the PRNP gene. Only a small percentage of all cases of prion disease run in families, however. Most cases of prion disease are sporadic, which means they occur in people without any known risk factors or gene mutations. In rare circumstances, prion diseases also can be transmitted by exposure to prion-contaminated tissues or other biological materials obtained from individuals with prion disease.