TTR and primary systemic amyloidosis: Among them, transthyretin, encoded by the TTR gene, is a central amyloidogenic protein involved in two distinct forms of systemic amyloidosis: wild-type transthyretin amyloidosis (ATTRwt), previously known as senile systemic amyloidosis, and hereditary transthyretin amyloidosis (ATTRv), formerly referred to as familial amyloid polyneuropathy [7].