Variant Creutzfeldt-Jakob disease: prion protein genotype analysis of positive appendix tissue samples from a retrospective prevalence study.

OBJECTIVE To perform prion protein gene (PRNP) codon 129 analysis in DNA extracted from appendix tissue samples that had tested positive for disease associated prion protein. DESIGN Reanalysis of positive cases identified in a retrospective anonymised unlinked prevalence study of variant Creutzfeldt-Jakob disease (vCJD) in the United Kingdom. STUDY SAMPLES Three positive appendix tissue samples out of 12,674 samples of appendix and tonsil tested for disease associated prion protein. The patients from whom these samples were obtained were aged 20-29 years at the time of surgery, which took place in 1996-9. SETTING Pathology departments in two tertiary centres in England and Scotland. RESULTS Adequate DNA was available for analysis in two of the three specimens, both of which were homozygous for valine at codon 129 in the PRNP. CONCLUSIONS This is the first indication that the valine homozygous subgroup at codon 129 in the PRNP is susceptible to vCJD infection. All tested clinical cases of vCJD have so far occurred in the methionine homozygous subgroup, and a single case of probable iatrogenic vCJD infection has been identified in one patient who was a methionine/valine heterozygote at this genetic locus. People infected with vCJD with a valine homozygous codon 129 PRNP genotype may have a prolonged incubation period, during which horizontal spread of the infection could occur either from blood donations or from contaminated surgical instruments used on these individuals during the asymptomatic phase of the illness.