PRNP and dementia: Human prion diseases are unusual amongst neurodegenerative diseases in having three different types of aetiology: as well as arising due to rare pathogenic mutations in PRNP encoding PrPC (inherited prion disease accounting for ∼10%–15% cases) and spontaneously (sporadic prion disease accounting for ∼85% cases), the disease can also be acquired through transmission between humans or zoonotically (<1% cases).3-5 Sporadic Creutzfeldt-Jakob disease (sCJD) is the most common human prion disease, which has a lifetime risk of ∼1:5000,6 and typically presents as a rapidly progressing dementia.