PRNP and fatal familial insomnia: Indeed, this form was termed the thalamic form of CJD or sporadic fatal insomnia (sFI), due to its close phenotypic and biochemical similarity to a genetic PrD, fatal familial insomnia (FFI), which is associated with the D178N mutation in the prion protein gene (PRNP) and methionine encoded in the mutated allele at codon 129[9].