Hi, from what I understand there are 3 main ways somebody can get a prion disease, and therefore 3 ways a protein can become a prion:
This involves somebody getting infected with a Prion disease and is very uncommon, accounting for less than 1% of cases.
The gene which codes for the protein PrP is called PRNP. When a person is healthy, the gene is translated to a functional, correctly folded protein. Some people have mutations which cause the PRNP gene to produce mutant PrP protein. This protein does not immediately for prions, but can do decades later. As the patient gets older the mutant PrP protein folds to produce prions, which causes a rapid deterioration in the person’s condition. This accounts for 15% of cases. A quick thing to note with this is that they are not always inherited, it can happen due to random mutation and 60% of genetic cases are not inherited.
This is when someone gets a prion disease and we do not know how it happens. This accounts for 85% of cases.