TTR and Familial transthyretin-related amyloidosis: 1,2 Mostly, TTR exists in serum by the form of tetramers. 2 When the structure of TTR monomers is disrupted, the stability of TTR tetramers would severely decline, which promotes the dissociation of TTR tetramers, aggregation of TTR monomers, and subsequent formation of amyloid in tissues, leading to transthyretin amyloidosis (ATTR). 3