The discrepancy between the low number of vCJD cases in the United Kingdom to date and the higher prevalence of infected humans estimated on the basis of retrospective biopsy analyses (27,28) indicates the existence of pre- or subclinical cases, perhaps as a result of a low-dose exposure to BSE-contaminated material or a less susceptible PRNP genotype. This evidence concerns the gene PRNP and variant Creutzfeldt-Jakob disease.