PRNP and fatal familial insomnia: Genetic human prion disease is associated with a range of mutations in the prion protein gene (PRNP) on Chromosome 20 [1], which include genetic or familial CJD, as well as other genetic human transmissible spongiform encephalopathies (TSE), such as Gerstmann-Sträussler-Scheinker disease (GSS) and fatal familial insomnia (FFI).