TRIM21 and familial long QT syndrome: <h4>Background</h4>The most investigated form of autoimmune-long-QT-syndrome (LQTS) is caused by circulating anti-Ro/SSA(Sjögren's syndrome-related antigen-A)-52kD antibodies, which cross-react with a specific sequence of the human ether-à-go-go-related (hERG) potassium channel's pore region, reducing the rapid inward-rectifying potassium current (I<sub>Kr</sub>) density.