Abstract 12094: Transient Outward Current (Ito) Gain-of-Function Mutation, G600R, in the KCND3 —Encoded Kv4.3 Channel and Brugada Syndrome
Introduction: Brugada syndrome (BrS) is a sudden death predisposing genetic condition associated so far with mutations in 8 BrS-susceptibility genes and is believed to account for 20% of autopsy negative sudden unexplained death syndrome (SUDS) cases. Given the prominent role of the transient outward current (Ito) in BrS pathogenesis, we hypothesize that rare gain-of-function mutations in KCND3 may serve as a pathogenic substrate for BrS and SUDS even though no mutations in the KCND3 —encoded Kv4.3 α-subunit have been described.
Methods: KCND3 comprehensive mutational analysis was conducted using PCR, DHPLC, and direct sequencing of DNA derived from 14 unrelated BrS patients (13 males, 36.0 ± 9.3 years, 70% white) and 122 unrelated SUDS cases (75 males, 17.5 ± 12.3 years, 89% white). DNA from 780 healthy individuals was examined to assess allelic frequency for all identified non-synonymous variants. The putative BrS- and SUDS-associated mutation was engineered by site directed mutagenesis and co-expressed with wild-type KChIP2 in HEK293 cells to re-capitulate the Ito current. Wild-type and mutant Ito currents were recorded using the whole cell patch clamp technique.
Results: Both a BrS and SUDS case (2/136, 1.5%) hosted the same novel missense mutation, G600R, absent in > 1500 reference alleles (p < 0.001), and involving a highly conserved residue. The BrS index case was a 22-year-old male with spontaneous coved-type ST-segment elevation in V1-V3, spontaneous atrial fibrillation, and a significant paternal family history of sudden death. The G600R-positive SUDS case was a 23-year-old male unexplained drowning victim with no significant past medical history. Both cases were BrS1–8 genotype negative. Co-expression of Kv4.3-G600R plus KChIP2-WT significantly increased Ito current density from −20 mV to +40 mV compared to Kv4.3-WT plus KChIP2-WT (n = 14 and 10 for each group, p <0.05). No statistical difference in the inactivation kinetics was observed between Kv4.3-G600R and Kv4.3-WT.
Conclusions: This study provides the first molecular and functional evidence implicating a KCND3 gain-of-function mutation in the pathogenesis of BrS and SUDS with the potential for a lethal arrhythmia being precipitated by a biogenic increase in Ito current.
- © 2010 by American Heart Association, Inc.