Distinct functional defect of three novel Brugada syndrome related cardiac sodium channel mutations

Abstract

The Brugada syndrome is characterized by ST segment elevation in the right precodial leads V1-V3 on surface ECG accompanied by episodes of ventricular fibrillation causing syncope or even sudden death. The molecular and cellular mechanisms that lead to Brugada syndrome are not yet completely understood. However, SCN5A is the most well known responsible gene that causes Brugada syndrome. Until now, more than a hundred mutations in SCN5A responsible for Brugada syndrome have been described. Functional studies of some of the mutations have been performed and show that a reduction of human cardiac sodium current accounts for the pathogenesis of Brugada syndrome. Here we reported three novel SCN5A mutations identified in patients with Brugada syndrome in Taiwan (p.I848fs, p.R965C, and p.1876insM). Their electrophysiological properties were altered by patch clamp analysis. The p.I848fs mutant generated no sodium current. The p.R965C and p.1876insM mutants produced channels with steady state inactivation shifted to a more negative potential (9.4 mV and 8.5 mV respectively), and slower recovery from inactivation. Besides, the steady state activation of p.1876insM was altered and was shifted to a more positive potential (7.69 mV). In conclusion, the SCN5A channel defect related to Brugada syndrome might be diverse but all resulted in a decrease of sodium current.

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

“…Those results were basically consistent with previous studies (16,17). As for R965C-R1309H mutations, compared to R1309H mutation, it induced more significant depolarization shift of activation curve, V 1/2 and slope factor, suggesting that Na v 1.5 R965C-R1309H channel was activated at the much more depolarized membrane potential and displayed slower activation (Supplement 3).…”

“…Consistent with previous literatures reported (16,17), as shown in the Figure 4A-C and Table 2, the R1309H mutation, but not R965C mutation, significantly reduced the Na + current density at a series of test potentials ranging from -45 mV to -15 mV when compared to the WT group (Supplement 1). More importantly, we found that R965C-R1309H mutations resulted in a more severe reduction in Na + current density ranging from -45 mV to 30 mV compared to the WT group.…”

“…And the slope factor (K) of R1309H mutation was significant amplified but not of R965C mutation when compared to the WT group. These above data were keeping with the previous studies (16,17). We were surprised to find that the inactivation curve of R965C-R1309H mutations most significantly shifted to the left with the increase of V 1/2 hyperpolarization and K value ( Figure 5C, Table 3).…”

“…According to previous studies, although R965C mutation carried by a sporadic case of Brugada syndrome didn't significantly change the current density of I Na , it produced sodium channel with impaired steady-state inactivation, slower inactivation, and recovery from inactivation. The substitution of R965C from the positively charged arginine to a neutral cysteine might influence channel gating properties (17). In another family, the proband carrying homozygous R1309H mutation which inherited from the parents of close cousins, showed with complex clinical phenotypes characterized as follows: one proband had phenotypes of atrial tachycardia, ventricular tachycardia, Brugada syndrome-like ST segment and T wave, and first degree atrioventricular block; the second proband was demonstrated with sinus bradycardia, P wave prolongation, first degree atrioventricular block and QRS prolongation, also suffered from atrial septal defect and ventricular septal defect requiring surgical closure; another sibling of 2-month old experienced sudden cardiac death induced by diarrheal illness was speculated to carry with homozygous R1309H mutation, although the genotype was unknown.…”

The genetic component of Brugada syndrome

“…Functional studies of many different mutations in the gene have been performed and they all lead to a reduction in net sodium current due to one or more of following reasons (Antzelevitch et al, 2005); (1) reduced current density due to failure of the sodium channel to express or defect trafficking of the channel (Baroudi et al, 2001; Valdivia et al, 2004; Pfahnl et al, 2007), (2) a shift in the voltage- and time-dependence of sodium channel current activation, inactivation or reactivation (Keller et al, 2005; Hsueh et al, 2009; Calloe et al, 2013), or (3) entry of the sodium channel into an intermediate state of inactivation from which it recovers relatively slower than normal (Bezzina et al, 1999; Veldkamp et al, 2000; Chiang et al, 2009). A number of knock-out mouse models support the central role of SCN5A in the pathogenesis of BrS (Killeen et al, 2008; Derangeon et al, 2012).…”