PRNP and prion disease: There are strong genetic susceptibility factors in prion disease, with ∼15% of cases being an inherited disease, all caused by mutation of the prion protein gene (PRNP).2 A small proportion is acquired, caused by the transmission of prions during blood transfusion, neurosurgery, via pituitary-derived growth hormone therapy or ingestion of bovine spongiform encephalopathy-contaminated food products.1