According to their etiology, human prion diseases can be divided into three groups: (1) sporadic CJD, that constitutes 85–90% of CJD cases; (2) diseases acquired by infection by external prions, such as in the case of Kuru, iatrogenic CJD, and variant CJD (2–5% of CJD cases); and (3) diseases caused by a genetic mutation in the prion (PRNP) gene, such as in the case of familial CJD, genetic CJD, GSS, and FFI (approximately, 10–15% of all prion diseases), with an autosomal dominant inheritance pattern [4]. The gene discussed is PRNP; the disease is prion disease.