TTR and Familial transthyretin-related amyloidosis: The liver and the choroid plexus are themajor sites of TTR synthesis.TTR transports the retinol-binding protein–retinol complexand functions as a backup carrier for thyroxine (T4) inthe blood and as a main transporter of T4 in the cerebrospinalfluid.3−5 The extracellular misfolding of TTR and subsequentaccumulation of amyloid fibrils in a variety of tissues underlie theonset of a group of disorders known as transthyretin amyloidosis (ATTR).6