Sheep carrying the PRNP polymorphisms valine (V) or alanine (A) at codon 136 (136V and 136A) are highly susceptible to classical scrapie, while the exchange of arginine (R) to histidine at codon 154 (154H) is linked to low scrapie susceptibility [1,2]. The gene discussed is PRNP; the disease is scrapie.