All of these human studies, in addition to the extremely prolonged and variable incubation periods seen in prion transmission experiments when crossing a species barrier, suggest that persons encoding any of the 3 human PrP codon 129 genotypes may be susceptible to vCJD, including secondary vCJD transmitted through blood transfusion, blood products, tissue and organ transplantation, and other iatrogenic routes. The gene discussed is PRNP; the disease is variant Creutzfeldt-Jakob disease.