In 1993, Prusiner suggested that the scrapie infectious agent may be an immunologically inert host encoded protein (PrPC) that could misfold into a pathologic form (PrPSc), by a conformational change of α-helices into a β-rich structure prone to undergo a liquid-to-solid phase transition, which is often called in the field ‘protein aggregation’. This evidence concerns the gene PRNP and scrapie.