FKBP1B and cardiac arrhythmia: We chose two mutations (described above) from human CPVT patients that were demonstrated to cause arrhythmia also in mice: The R4743C mutation, analogous to the CPVT mutation R4497C in humans (R4496C in mice; resulting in a leaky channel24,30), and R2729S analogous to the CPVT mutation R2474S in humans and mice (resulting in weak calstabin-2 binding24,25 and/or defective interdomain interactions28).