A total of 51 goats, including seven clinical cases, from the first herd in Greece reported to have scrapie was examined to discern an association between scrapie susceptibility and polymorphisms of the gene encoding the prion protein (PrP). Each animal was evaluated for clinical signs of the disease, histopathological lesions associated with scrapie, the presence of detectable proteaseresistant PrP in the brain and PrP genotype. Eleven different PrP genotypes encoding at least five unique predicted mature PrP amino acid sequences were found. These genotypes included the amino acid polymorphisms at codons 143 (H R) and 240 (S P) and ' silent ' nucleotide alterations at codons 42 (a g) and 138 (c t). Additionally, novel caprine amino acid polymorphisms were detected at codons 21 (V A), 23 (L P), 49 (G S), 154 (R H), 168 (P Q) and 220 (Q H) and new silent mutations were found at codons 107 (g a) and 207 (g a). The following variants were found in scrapie-

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A total of 216 local crossbred sheep from 16 scrapie-affected Greek flocks and 210 purebred sheep of the milk breeds Chios and Karagouniko from healthy flocks were analysed for scrapie-linked polymorphisms in the prion protein (PrP) gene. Of the 216 sheep in this case-control study, 96 sheep were clinical cases, 25 subclinical cases (asymptomatic at the moment of euthanasia but positive by histopathology and/or ELISA detecting proteinase-resistant PrP) and 95 healthy controls (negative by all evaluations). Polymorphisms at codons 136, 154 and 171 were determined by denaturing gradient gel electrophoresis, followed by RFLP and sequencing. Scrapie, both clinical and subclinical, was associated with the genotypes ARQ/ARQ (88 of 110 sheep of that genotype), ARQ/TRQ (9 of 13), ARQ/AHQ (15 of 38) and VRQ/VRQ (9 of 17). Histopathological lesions were more severe in the clinical cases. Genotypes ARQ/ARR (26 sheep), ARQ/ARK (seven sheep), AHQ/ARR (one sheep), ARH/ARH (one sheep) and ARR/ARH (three sheep) were detected exclusively in healthy control sheep. In the purebred survey, four genotypes were present in the Chios sheep (ARQ/ARQ, ARQ/TRQ, ARQ/AHQ and ARQ/ARR) and four in the Karagouniko sheep (ARQ/ARQ, ARQ/AHQ, ARQ/ARR and ARQ/ARH). INTRODUCTIONScrapie is an infectious neurodegenerative fatal disease of sheep and goats belonging to the group of transmissible subacute spongiform encephalopathies (TSEs), along with bovine spongiform encephalopathy (BSE), chronic wasting disease and Creutzfeldt-Jakob disease. All TSEs are characterized by long incubation periods, disturbances in behaviour and movement, degeneration in tissues of the central nervous system (CNS) and accumulation of an abnormal isoform of the host-encoded cellular prion protein in tissues of the CNS. It has been hypothesized that these diseases are attributable to a conformational change in the prion protein (PrP), which results in a change from a predominantly a-helical protein to a b-sheet form (Prusiner, 1996). Normal PrP protein (PrP c ) is a cell-surface glycoprotein, the expression of which is necessary for the production of prions (Büeler et al., 1993;Prusiner et al., 1993). PrP c is expressed in most tissues of the body, with the nervous tissues showing the highest PrP c expression levels (Bendheim et al., 1992;Horiuchi et al., 1995).In several animal species and in humans, polymorphisms within the open reading frame of the PrP gene are associated with the occurrence and the pathological lesions of TSEs (Pocchiari, 1994). The incidence of natural scrapie is strongly influenced by alterations in the host gene that encodes the PrP (Hunter, 1997). Such polymorphisms may influence the conversion of PrP c into the pathogenic isoform . The mechanism by which the individual allelic variants lead to altered susceptibility or incubation periods has not been elucidated. It has been proposed that in humans PrP polymorphisms may be present at critical sites involved in the conformational transition from PrP c to PrP Sc (Glockshuber et al., 1999). The study o...

The association between PRNP variation and scrapie incidence was investigated in a highly affected Greek goat herd. Four mutations were identified at codons 171Q/R, 211R/Q, 222Q/K and 240P/S. Lysine at codon 222 was found to be associated with the protection from natural scrapie (P50.0111). Glutamine at codon 211 was observed in eight animals, all of them being scrapie-negative, indicating a possible protective role of this polymorphism although statistical analysis failed to support it (P50.1074). A positive association (P50.0457) between scrapieaffected goats and the wild-type Q 171 R 211 Q 222 S 240 allele is presented for the first time. In addition, a novel R 171 RQS allele, which is identical to the A 136 R 154 R 171 allele that has been associated with resistance to classical scrapie in sheep, was observed in low frequency. Resistant alleles that include K 222 and Q 211 are absent or rare in sheep and can provide the basis for the development of a feasible breeding programme for scrapie eradication in goats.