PRNP and Cowden syndrome 1: The incidence of CS is highly dependent on the genotype of the ovine prion protein gene (PRNP) at codons 136, 154 and 171 with animals homozygous for the VRQ allele (expressing valine (V), arginine (R) and glutamine (Q) respectively at these positions) at very high risk of disease and animals homozygous for the ARR allele (expressing alanine (A), arginine (R) and arginine (R) respectively) at the lowest risk [3, 5].