PRNP and variant Creutzfeldt-Jakob disease: However, we cannot discount the possibility that that these differences in tissue distribution are caused by the hematogenous route of infection in this person (as opposed to the probable oral route in patients with clinical vCJD) or the difference between the PRNP gene codon 129 genotype of the asymptomatic vCJD–affected person (PRNP gene codon 129 Met/Val) and persons with clinical vCJD (PRNP gene codon 129 Met/Met).