We selected three PRNP variants, which are also followed by amino acid substitutions (P102L, P105L, and D178N) and appear to be associated with susceptibility to various prion diseases such as Gerstmann-Sträussler-Scheinker disease (GSS) and fatal familial insomnia (FFI) [22]–[25]. The gene discussed is PRNP; the disease is fatal familial insomnia.