TRIM21 and familial long QT syndrome: 1. direct binding in HEK293-hERG cells incubated with purified IgGs from anti-Ro/SSA-positive CTD patients with LQTS 2. direct binding in HEK293-hERG cells and guinea-pig ventricular tissue incubated with anti-Ro/SSA-positive sera from Ro52kD-immunized guinea-pigs 3. cross-reactivity with a 31–amino acid peptide corresponding to the pore-forming region (segment S5-S6) incubated with sera from anti-Ro/SSA-positive CTD patients with LQTS