[69] Paradoxically, many of these in vitro approaches to this website prion disease research have been developed using materials from high-titer rodent models of sheep scrapie. The challenge for human prion disease research is to apply these emerging techniques to the study of human prions in humans. Molecular strain typing in the form of classifying the mobility and glycoform ratio of protease-resistant prion protein by Western blotting is a remarkably useful adjunct to neuropathological assessment during the post-mortem diagnosis of human prion diseases

(Fig. 1). The glycoform ratio difference between vCJD and all forms of sCJD is a remarkably robust phenomenon, although the mechanism underlying it remains obscure. All cases of vCJD examined show type 2B PrPres, irrespective of brain region assayed and the PrPres type is also found in lymphoreticular tissues, albeit with presumably tissue-specific minor modification of mobility and an accentuation of the glycoform ratio. Similarly sCJD cases are characterized by a narrow range of glycoform ratios, distinct from vCJD, and the presence of either type 1 or type 2 PrPres (type 1A and type 2A). The PrPres types found in the brain in iCJD and kuru resemble those found in sCJD (type 1A and type 2A), from which they were presumably derived. Individual cases of gCJD, GSS and FFI usually check details have type

1 or type 2 PrPres, but with a glycoform ratio in which the non-glycosylated component is under-represented (which we have termed A/B). However, this is not always true and a broad spectrum of glycoform ratios can be found in genetic prion diseases. Moreover, some cases of GSS are characterized by an approximately 8 kDa (N- and C-terminally truncated) PrPres fragment, and some cases of FFI have little detectable PrPres at all. Despite the diagnostic utility, a simple

one-to-one correspondence between PrPres type and disease phenotype (and by implication to agent strain) seems unlikely in principle and is complicated by the facts. First, the choice of analyzing only that fraction of PrPSc which ID-8 survives a particular concentration of protease may seem arbitrary. Second, the interpretation of a molecular population variable, such as glycosylation site occupancy, as conforming to two or three discrete types, could be seen as simplistic. Lastly, protease digestion may be considered to be a somewhat blunt instrument to distinguish secondary and higher-order conformational differences in PrPSc. Even when genotype (mutations and polymorphisms) is taken into account, three major types (1, 2, 8 kDa) and three wild-type genotypes (MM, MV and VV) provide insufficient molecular variation to account for all the phenotypic variations observed. For example, two forms of sCJD share methione homozygosity and type 2A PrPres but one form closely resembles FFI (without the causative mutation) and the other is CJD-like.