Key result
The novel CACNA1C R511Q mutation causes non-syndromic type-8 long QT syndrome by significantly increasing persistent calcium currents (10.8% vs 3.3% for wild-type, P<0.01) and delaying voltage-dependent inactivation.
Why the study?
Mutations in the Cav1.2 DI-II linker were associated with syndromic LQT8 but not non-syndromic LQT8, prompting investigation of the biophysical defects of a novel CACNA1C mutation in this region.
Does the CACNA1C R511Q mutation alter the biophysical properties of the Cav1.2 channel in non-syndromic long QT syndrome?
Does the CACNA1C R511Q mutation alter the biophysical properties of the Cav1.2 channel in non-syndromic long QT syndrome?
Absolute Event Rate: 10.8% vs 3.3%
p-value: p=<0.01
The novel CACNA1C R511Q mutation causes non-syndromic type-8 long QT syndrome by delaying voltage-dependent inactivation and increasing persistent and window calcium currents.
Supports R511Q as pathogenic in non-syndromic LQT8; leaves open clinical translation pending human validation.
BACKGROUND: Gain-of-function mutations in CACNA1C encoding Cav1.2 cause syndromic or non-syndromic type-8 long QT syndrome (LQTS) (sLQT8 or nsLQT8). The cytoplasmic domain (D)Ⅰ-Ⅱ linker in Cav1.2 plays a pivotal role in calcium channel inactivation, and mutations in this site have been associated with sLQT8 (such as Timothy syndrome) but not nsLQT8. OBJECTIVE: Since we identified a novel CACNA1C mutation, located in the DⅠ-Ⅱ linker, associated with nsLQTS, we sought to reveal its biophysical defects. METHODS: Target panel sequencing was employed in 24 genotype-negative nsLQTS probands (after Sanger sequencing) and three family members. Wild-type (WT) or R511Q Cav1.2 was transiently expressed in tsA201 cells, then whole-cell Ca2+ or Ba2+ currents (ICa or IBa) were recorded using whole-cell patch-clamp techniques. RESULTS: We identified two CACNA1C mutations, a previously reported R858H mutation and a novel R511Q mutation located in the DⅠ-Ⅱ linker. Four members of one nsLQTS family harbored the CACNA1C R511Q mutation. The current density and steady-state activation were comparable to those of WT-ICa. However, persistent currents in R511Q-ICa were significantly larger than those of WT-ICa (WT at +20 mV: 3.3±0.3%, R511Q: 10.8±0.8%, P<0.01). The steady-state inactivation of R511Q-ICa was weak in comparison to that of WT-ICa at higher prepulse potentials, resulting in increased window currents in R511Q-ICa. Slow component of inactivation of R511Q-ICa was significantly delayed compared to that of WT-ICa (WT-tau at +20 mV: 81.3±3.3 ms, R511Q-tau: 125.1±5.0 ms, P<0.01). Inactivation of R511Q-IBa was still slower than that of WT-IBa, indicating that voltage-dependent inactivation (VDI) of R511Q-ICa was predominantly delayed. CONCLUSIONS: Delayed VDI, increased persistent currents, and increased window currents of R511Q-ICa cause nsLQT8. Our data provide novel insights into the structure-function relationships of Cav1.2 and the pathophysiological roles of the DⅠ-Ⅱ linker in phenotypic manifestations.
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Nakajima et al. (2022) studied Non-syndromic long QT syndrome (n=27). CACNA1C R511Q mutation vs. Wild-type CACNA1C was evaluated on Persistent calcium currents at +20 mV (p=<0.01). The novel CACNA1C R511Q mutation causes non-syndromic type-8 long QT syndrome by significantly increasing persistent calcium currents (10.8% vs 3.3% for wild-type, P<0.01) and delaying voltage-dependent inactivation.
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