TTR and familial amyloid neuropathy: ATTRwt amyloidosis is caused by the misfolding into amyloid fibrils of the native, genetically normal, transthyretin (TTR) protein, whereas ATTRv amyloidosis is caused by misfolding and fibril aggregation due to destabilization of the protein tetramer that is caused by a single amino acid substitution in the TTR gene.