The misfolded form (PrPSc or prion) of the naturally occuring prion protein (PrPC or cellular PrP) is responsible for neurodegenerative diseases such as Creutzfeldt-Jakob disease (CJD), bovine spongiform encephalopathy (BSE) (also known as ‘mad cow disease’) and a new variant of CJD (vCJD), which is thought to be caused by ingestion of cattle-derived foodstuffs contaminated with prions. This evidence concerns the gene PRNP and variant Creutzfeldt-Jakob disease.