Transient outward current (Ito) gain-of-function mutations in the KCND3-encoded Kv4.3 potassium channel and Brugada syndrome

Abstract

Background Brugada syndrome (BrS) is a sudden death predisposing genetic condition characterized electrocardiographically by ST-segment elevation in the leads V1-V3. Given the prominent role of the transient outward current (Ito) in BrS pathogenesis, we hypothesized that rare gain-of-function mutations in KCND3 may serve as a pathogenic substrate for BrS. Methods Comprehensive mutational analysis of KCND3-encoded Kv4.3 (Ito) was conducted using PCR, DHPLC, and direct sequencing of DNA derived from 86 unrelated BrS1-8 genotype negative BrS patients. DNA from 780 healthy individuals was examined to assess allelic frequency for non-synonymous variants. Putative BrS-associated Kv4.3 mutations were engineered and co-expressed with wild-type KChIP2 in HEK293 cells. Wild-type and mutant Ito ion currents were recorded using whole cell patch clamp. Results Two BrS1-8 genotype-negative cases possessed novel Kv4.3 missense mutations. Both Kv4.3-L450F and Kv4.3-G600R were absent in 1560 reference alleles and involved residues highly conserved across species. Both Kv4.3-L450F and Kv4.3-G600R demonstrated a gain-of-function phenotype, increasing peak Ito current density by 146.2% (n=15, p<0.05) and 50.4% (n=15, p<0.05) respectively. Simulations employing a Luo-Rudy II AP model demonstrated the stable loss of the AP dome as a result of the increased Ito maximal conductance associated with the heterozygous expression of either L450F or G600R. Conclusions These findings provide the first molecular and functional evidence implicating novel KCND3 gain-of-function mutations in the pathogenesis and phenotypic expression of BrS, with the potential for a lethal arrhythmia being precipitated by a genetically enhanced Ito current gradient within the right ventricle were KCND3 expression is the highest.

Brugada syndrome: clinical and genetic findings

“…62 Gain-of-function pathogenic variants in the KCND3-encoded K v 4.3 potassium channel are implicated in the pathogenesis and phenotypic expression of BrS, inducing lethal arrhythmia that has been precipitated by a genetically enhanced I to current gradient within the right ventricle. 63 Interestingly, the KCNE5 gene is located on the X chromosome, adding a new pattern of inheritance for BrS. 64 Hence, pathogenic variations in KCNE5 cause a gain-of-function effect on I to current gradients.…”

Ionic and Cellular Mechanisms Underlying the Development of Acquired Brugada Syndrome in Patients Treated with Antidepressants

“…9,14 Mutations in glycerol-3-phophate dehydrogenase 1-like enzyme gene (GPD1L, BrS2), SCN1B (β1-subunit of Na channel, BrS5), KCNE3 (MiRP2; BrS6), SCN3B (β3-subunit of Na channel, BrS7), KCNJ8 (BrS8), and KCND3 (BrS10) are more rare. [10][11][12]15,16,34 These genetic defects cause a loss of function of I Na or I Ca , or a gain of function of I to . These and other genetic variants may give rise to subclinical forms of BrS, that can predispose to acquired forms of BrS developing following administration of antidepressants such as amitriptyline and pharmacological agents with similar actions.…”

“…Mutations leading to loss of function in I Na and I Ca , as well as those giving rise to a gain of function in I to , have been identified as genetic causes of BrS. [6][7][8][9][10][11][12][13][14][15][16][17] BrS has thus far been associated with mutations in 11 different genes.…”

Genetic Basis of Brugada Syndrome

“…Pathogenic mutations in this gene have been associated with LQTS, SIDS, AF and BrS (Figure 2). In 2011, Giudicessi et al [47] provide the first molecular and functional evidence implicating novel KCND3 gain-of-function mutations (Kir4.3 protein) in the pathogenesis and phenotypic expression of BrS, with enhanced I to current gradient within the right ventricle where the KCND3 gene expression is the highest. Currently, two pathogenic mutations have been associated with BrS, p.Leu450Phe (c.1348C>T, p.L450F) (CM111334), and p.Gly600Arg (c.1798G>C, p.G600R) (CM1110945) [48] despite this last variation was reported in a SUDS case with no confirmed BrS, so far.…”