Inherited prion diseases such as familial Creutzfeldt-Jakob disease (fCJD), fatal familial insomnia (FFI), and Gerstmann-Sträussler-Scheinker disease (GSS) are all caused by pathogenic PrP mutations [2–4], whereas sporadic and infectious forms of prion disease are caused by the misfolding of normal wild-type PrP (PrPC) into an infectious conformer (PrPSc) [5,6]. This evidence concerns the gene PRNP and fatal familial insomnia.