Several experimental therapeutics have shown promise in animal prion diseases and are being developed with a view to human studies.14–16 Therefore there is an unmet need for biomarkers, which have utility for experimental medicine: those, which provide objective evidence of disease progression in symptomatic patients, and which predict clinical onset in individuals at-risk of disease because they have been exposed to prions or carry a PRNP mutation. Here, PRNP is linked to prion disease.