TTR and familial amyloid neuropathy: Variant TTR is commonly a less stable circulating tetramer than wild-type TTR and tends to infiltrate tissue with subsequent reduction in TTR serum levels.24 This phenomenon represents the rationale for the potential clinical use of serum TTR as a screening biomarker for ATTRv amyloidosis and as a tool to assess response to treatment in both ATTRwt and ATTRv amyloidosis.