Novel CACNA1C R511Q mutation, located in domain I-II linker, causes non-syndromic type-8 long QT syndrome

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 (I-Ca or I-Ba) 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 D?-? 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-I-Ca. However, persistent currents in R511Q-I-Ca were significantly larger than those of WT-I-Ca (WT at +20 mV: 3.30.3%, R511Q: 10.8 +/- 0.8%, P<0.01). The steady-state inactivation of R511Q-I-Ca was weak in comparison to that of WT-I-Ca at higher prepulse potentials, resulting in increased window currents in R511Q-I-Ca. Slow component of inactivation of R511Q-I-Ca was significantly delayed compared to that of WT-I-Ca (WT-tau at +20 mV: 81.3 +/- 3.3 ms, R511Q-tau: 125.1 +/- 5.0 ms, P<0.01). Inactivation of R511Q-I-Ba was still slower than that of WT-I-Ba, indicating that voltage-dependent inactivation (VDI) of R511Q-I-Ca was predominantly delayed. Conclusions Delayed VDI, increased persistent currents, and increased window currents of R511Q-I-Ca 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.