TTR and primary systemic amyloidosis: In some other instances, amyloid formation occurs in the absence of other apparent predisposing conditions, as a process associated to aging, presumably due to the intrinsic amyloidogenicity of a specific protein, as in the case of sporadic forms of Alzheimer’s and prion diseases, as well as in the case of systemic amyloidosis associated to wild-type TTR (ATTRwt amyloidosis) (Prusiner, 2001; Gertz et al., 2015; Long and Holtzman, 2019).