More Severe Loss-of-Function Sodium Channel induced by Compound SCN5A R965C and R1309H Mutants lead to Complex Familial Arrhythmia Syndrome.

[Abstract]O_ST_ABSObjectiveC_ST_ABSA complex familial arrhythmia syndrome was identified in a Chinese Han family, characterized by sick sinus syndrome, progressive conduction block, atrial fibrillation, atrial standstill and Brugada syndrome. The underlying mechanism associated with the genetic mutation was investigated.\n\nMethodsGenetic analysis was conducted for probands in the coding and splicing regions of genes susceptible to cardiac arrhythmia diseases. The stable cell lines overexpressing wild-type (WT) or mutant SCN5A gene were generated in HEK293T cells and electrophysiological recordings were performed to evaluate the functional changes of mutant NaV1.5 channels.\n\nResultsWe identified a rare double R965C and R1309H mutations in NaV1.5 channel, as a heterozygous and compound pattern, locating in the same chromosome. Compared to WT, a single mutation of R965C or R1309H, the compound mutations of R965C-R1309H most dramatically reduced the peak current of NaV1.5 channel with testing potentials ranging from -35 mV to 25 mV. Notably, the maximal peak current of NaV1.5 channel carrying R1309H only and R965C-R1309H mutations displayed significant decreases by 31.5% and 73.34%, respectively, compared to WT. Additionally, compared to single mutations of R965C or R1309H, the R965C-R1309H mutations resulted in more obviously depolarization-shifted activation and hyperpolarization-shifted inactivation, also caused most significantly changed time constant, V1/2 and slope factor of activation and inactivation.\n\nConclusionsThe compound mutations of R965C-R1309H led to more dramatically reduced current density of Nav1.5 channel, as well as more depolarization-shifted activation and hyperpolarization-shifted inactivation than single mutation of R965C or R1309H, which may provide more understanding on the molecular mechanisms underlying the familial arrhythmia syndrome.\n\nAuthor summarySeveral limited types of research about the interaction of compound mutations and the mechanism of interaction remains controversial. Here we report a novel compound mutation R965C-R1309H in SCN5A gene.The compound mutations of R965C-R1309H markedly reduced the Na+ current density of Nav1.5 channel and caused significant depolarization-shifted activation and hyperpolarization-shifted inactivation, suggesting that R965C mutation aggravated the pore gating changes of sodium channel containing R1309H mutation. The R965C located in the S4-like region in the intracellular loop between DII and DIII, and the R1309H located in the S4 helix of DIII as voltage sensor, which thus potentially had synergistic and interacting effects on pore gating properties of the sodium channel. Additionally, the complex familial arrhythmia syndrome simultaneously complicated of early young onset of arrhythmia and harmful prognosis of recurrent ischemic cerebral stroke, even though effective Warfarin anticoagulation.