An African loss-of-function CACNA1C variant p.T1787M associated with a risk of ventricular fibrillation

Figure 1. Family pedigrees of Cases 1 to 5 (A–E) with the members carrying CACNA1C variants. The probands are indicated by an arrow. Males are represented by squares, females by circles, affected subjects by filled symbols, and healthy subjects by open symbols. Cavα1c missense variants or their absence (no) are indicated below each subject that has been genotyped.

Figure 2. Electrocardiograms of Cases 1 and 2. Case 1, (A) just after reanimation showing early repolarisation pattern, (B) 5 years later. Case 2, (C) short-coupled torsades de pointes, (D) short-coupled premature ventricular beats.

Figure 3. Loss-of-function of Cavα1c-T1787M variant: calcium currents (ICa). (A) Representative whole-cell ICa traces showing the decrease of current density with the Cavα1c-T1787M variant compare to WT. (B) Current-voltage relationships in cells transfected with either WT (○) or Cavα1c-T1787M variants (●) of calcium channels (*p < 0.05). (C) Steady-state inactivation and activation curves of either WT (white symbol) or Cavα1c-T1787M variants (back symbol) of calcium channels showing no major alterations. (D) Calcium-dependent inactivation (CDI) with either WT (○) or Cavα1c-T1787M variants (●) of calcium channels showing no alterations. The number of cells is indicated in parentheses.

Figure 4. Loss-of function of Cavα1c-T1787M variant: barium currents (IBa). (A) Representative whole-cell IBa traces showing the decrease of current density with the Cavα1c-T1787M variant compare to WT. (B) Current-voltage relationships in cells transfected with either WT (○) or Cavα1c-T1787M variants (●) of calcium channels (*p < 0.05). (C) Steady-state inactivation and activation curves of either WT (white symbol) or Cavα1c-T1787M variant (back symbol) of calcium channels showing no major alterations. (D) Voltage-dependent inactivation (VDI) with either WT (○) or Cavα1c-T1787M variant (●) of calcium channels showing an increase of the VDI (*p < 0.05 and **p < 0.01). The number of cells is indicated in parentheses.

Figure 5. Scheme of the C-terminal part of the voltage-gated calcium channel. Schematic representation modified from Lyu et al. 2017 showing the C-terminal domain of Cavα1c with EF-hand like region (EF), pre-IQ, IQ, PCRD, DCRD, and CaM-competitive domain (CCD)62. The interaction between the PCRD and the DCRD forming the auto-inhibitory complex and the different sites of interaction with CaM (pre-IQ, IQ, and CCD) are depicted with dashed arrows. Asterisks correspond to human loss-of-function variants (present data, red)22. The in vivo cleavage site by proteolysis correspond to 1764-NANINNANN-1772 in human. The scissors show the position of the truncation of Cavα1c subunit performed in this study (A1770, 1800 in rabbit).

Figure 6. The IBa inhibition mediated by the cleaved CT part on the CT-cleaved Cavα1c construct is stronger when the Cavα1c-T1787M variant is present. (A) Representative raw traces of IBa density recorded in presence of CT-cleaved Cavα1c alone or with either WT or T1787M-cleaved CT part. (B) I-V relationships showing the effect mediated by T1787M variant on the CT-cleaved Cavα1c when introduced in the cleaved CT part (*p < 0.05: CT-cleaved Cavα1c + WT-cleaved CT vs CT-cleaved Cavα1c + T1787M-cleaved CT). The number of cells is indicated in parentheses.