PRNP codon 129 genotype has been shown to be a major factor influencing disease characteristics of Creutzfeldt-Jakob disease (8), but it has not been established if the same is true of vCJD, because previous vCJD infections in 129MV persons exposed to contaminated blood products have been asymptomatic (9,10). This evidence concerns the gene PRNP and variant Creutzfeldt-Jakob disease.