From Chemical & Engineering News, April 5, 1999
The formation of this incredibly stable & yet very debilitating structure is thought to occur in the intermediate step between completely unfolded & completely folded protein. (As seen below) This may be caused by just one point mutation, as discussed earlier with transthyritin.
It is thought that conditions causing a partially unfolded state are the cause of amyloid formation. Only a few proteins are actually involved in amyloid diseases, but it has been shown through experiment that proteins can be induced to form amyloid fibrils. This was accomplished by exposing acylphosphatase, a protein not previously implicated in amyloid disease, to trifluoroethanol (which generates a partially unfolded state of proteins in which the hydrogen bonds between peptide groups are still stable). After a period of time under the chosen conditions, acylphosphatase formed amyloid fibriles with all the characteristics of proteins normally associated with amyloid disease.