PRNP and scrapie: Thus, eight PRNP codons and an octapeptide repeat have been associated with various forms of ovine prion disease, i.e. classical scrapie (codons 112, 136, 137, 154, 171, and 176), atypical scrapie (codon 141 and an octapeptide repeat insertion) and experimental BSE (codon 168).