polypeptide chain adopting several distinct conformations within the amyloid core . Fibril polymorphism is strongly modulated by extrinsic factors and consequently, structures of fibrils formed in vitro often do not correspond to those isolated ex vivo from patients' tissues . Moreover, several polymorphs have been identified in a single test tube in which initially highly pure soluble protein (α-Synuclein) aggregated under well-defined solution conditions . Altogether, it is now increasingly more apparent that the free-energy landscape of amyloids is much more degenerate than perhaps originally thought, and that fibril polymorphism is a consequence of the interplay between kinetic factors and stability of individual conformations.