PRNP and scrapie: Sheep that express the ovine PrP variant V136R154Q171 (termed VRQ, where V, R and Q stand for valine, arginine and glutamine, respectively) or A136R154Q171 (termed ARQ, where A stands for alanine) are susceptible to classical scrapie (Clouscard et al. 1995; Goldmann et al. 1994).