Volume 13, Issue 1, Pages 122-131 (January 2016) Stop-codon and C-terminal nonsense mutations are associated with a lower risk of cardiac events in patients with long QT syndrome type 1  Martin H. Ruwald, MD, PhD, Xiaorong Xu Parks, PhD, Arthur J. Moss, MD, Wojciech Zareba, MD, PhD, Jayson Baman, BS, Scott McNitt, MS, Jorgen K. Kanters, MD, Wataru Shimizu, MD, Arthur A. Wilde, MD, PhD, Christian Jons, MD, PhD, Coeli M. Lopes, PhD  Heart Rhythm  Volume 13, Issue 1, Pages 122-131 (January 2016) DOI: 10.1016/j.hrthm.2015.08.033 Copyright © 2016 Heart Rhythm Society Terms and Conditions

Figure 1 Schematic drawing of the KCNQ1 potassium channel subunit. Frequency and location of the mutations including the A344sp in the membrane-spanning unit and R518X and Q530X in the C-terminal region of the channel. The size of the circles represents the number of patients with mutations at the respective locations. Heart Rhythm 2016 13, 122-131DOI: (10.1016/j.hrthm.2015.08.033) Copyright © 2016 Heart Rhythm Society Terms and Conditions

Figure 2 A: Kaplan-Meier estimates of cumulative probability of cardiac events in patients with long QT syndrome type 1 (LQT1) stratified by location and type of mutations. Stop-codon mutations are associated with a lower risk of cardiac events, and missense cytoplasmic loop (c-loop) mutations are associated with increased risk. B: Kaplan-Meier estimates of cumulative probability of aborted cardiac arrest (ACA) or sudden cardiac death (SCD) in patients with LQT1 stratified by location and type of mutations. Stop-codon mutations are associated with a lower risk of cardiac events, and missense c-loop mutations are associated with increased risk. Heart Rhythm 2016 13, 122-131DOI: (10.1016/j.hrthm.2015.08.033) Copyright © 2016 Heart Rhythm Society Terms and Conditions

Figure 3 A: Kaplan-Meier estimates of cumulative probability of cardiac events in long QT syndrome type 1 (LQT1) in patients with stop-codon mutations. A C-terminal (C-term) location was associated with a lower risk of cardiac events as compared with a non–C-term location. B: Kaplan-Meier estimates of cumulative probability of cardiac events in LQT1 in patients with nonmissense mutations. A C-term location was associated with a lower risk of cardiac events as compared with a non–C-term location. Heart Rhythm 2016 13, 122-131DOI: (10.1016/j.hrthm.2015.08.033) Copyright © 2016 Heart Rhythm Society Terms and Conditions

Figure 4 Functional effect of the 2 most common stop-codon mutations. A–D: Typical current traces of (WT+WT)/E1 (panel A), WT/E1 (panel B), (R518X+WT)/E1 (panel C), and (Q530X+WT)/E1 (panel D) subunits expressed on HEK293T cells; these traces are from a holding potential of −80 mV to a series of 3-second voltage steps between −40 and +100 mV in 20-mV intervals followed by a −20-mV step. Traces at +40-mV voltage step are shown in red. E: Summary data of peak current density at +40 mV. F: Summary data of Gmax of the tail current-voltage plot. Gmax was normalized to cell membrane capacitance. G: Summary data of V1/2 of the tail current-voltage plot. Error bars are standard errors of the mean. The number of cells measured for each mutant are indicated in the graphs. WT = wild type. Heart Rhythm 2016 13, 122-131DOI: (10.1016/j.hrthm.2015.08.033) Copyright © 2016 Heart Rhythm Society Terms and Conditions