A novel CACNA1C mutation identified in a patient with Timothy syndrome without syndactyly exerts both marked loss- and gain-of-function effects

Figure 1. Electrocardiograms. A: One year after the cardiac event. B: Day of admission. C: At left: Electropherograms of p.S643F. At right: Amino acid sequence alignments of p.S643F. D: Predicted topology of the CaV1.2 α subunit. Pink-filled circles indicate positions of mutations causing TS, and orange-filled triangles those of mutations causing TS without syndactyly. Yellow-filled diamonds denote mutations causing only LQTS phenotype without extracardiac features. AID = α1 interacting domain; D = domain; LQTS = long QT syndrome; S = segment; TS = Timothy syndrome.

Figure 2. Functional analysis of the mutant Cav1.2 channels. A: Whole-cell current representative recordings of wild-type (WT) and mutant Ca2+ channels. Peak inward current-voltage relationships were constructed by applying 1-s pulses from a holding potential of −70 mV to potentials ranging from −50 to +40 mV (upper). Representative traces of currents elicited at 0 mV and +20 mV from a holding potential of −70 mV at baseline (lower). B: Peak inward current-voltage relationship for WT (black circles, n = 18) and S643F (red triangles, n = 15). Peak inward currents were normalized to cell capacitance to give a measure of Ca2+ current density. ∗P < .05, ∗∗P < .01. C: The relationship between remaining currents at 500 ms depolarization and voltage for WT (black circles, n = 18) and S643F (red triangles, n = 15). D: Conductance-voltage activation curves for WT (black circles, n = 18) and S643F (red triangles, n = 15). E: Time constants for the voltage dependence of inactivation in WT (black circles, n = 18) and S643F (red triangles, n = 15). ∗P < .05, ∗∗P < .01.

Figure 3. A: To study the voltage dependence of inactivation, two-step voltage protocol, as indicated in the bottom right inset, was employed. Upper two sets traces are representative records. B: Conductance-voltage inactivation curves of Ca2+ current for wild-type (WT) (black circles, n = 15) and S643F (red triangles, n = 11). C: Conductance-voltage inactivation curves of Ba2+ current for WT (black circles, n = 10) and S643F (red triangles, n = 7).

Supplementary Figure 1. ECGs demonstrate T wave inversion in all leads except aVR (A) and torsades de pointes (B).