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 Ca(2+) or Ba(2+) 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 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-I(Ca). However, persistent currents in R511Q-I(Ca) were significantly larger than those of WT-I(Ca) (WT at +20 mV: 3.3±0.3%, 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.