See: prp, gerstmann straussler scheinker syndrome. Suggested as the causative agents of several infectious diseases such as scrapie (in sheep), kuru and Creutzfeld Jakob disease in man. They also cause spongiform diseases. Prions (proteinaceous infective particles) apparently contain no nucleic acid. The 27 kd protein of scrapie is related to a normal cell protein and may possibly cause its over production.