Prion strain variation and the type of CJD

Investigation into the nature of prions found in different diseases shows that there exists a variety of types or "strains" of prion protein. These strains appear to differ from eachother in animal prion disease by their differing incubation times, patterns of neuropathology and differing susceptibilty to proteolysis and subsequent migration patterns on polyacrylamide gel.

Study of human prion disease has revealed that prions found in human disease may be characterised into 4 types.

Types 1 and 2 are found in sporadic classical CJD and also in some iatrogenic cases.

Type 3 prions are found in iatrogenic cases of CJD, such as hormonal therapy where infection is acquired by peripheral injection.

Examining cases of the new variant CJD revealed a distinct new fourth type or strain of prion protein - appears particularly protease resistant and whose western blot suggests glycosylation of the protein.

• this fourth type of prion protein resemble closely those of bovine spongiform encephalopathy transmitted to mice, domestic cats and macaque monkeys