Abstract 20293: Molecular Genomic and Functional Association of Brugada and Early Repolarization Syndromes with S422L missense mutation in KCNJ8
Introduction: ATP-dependent potassium (KATP) channels in the cardiac sarcolemmal membrane consist of inward rectifying channel subunits Kir6.1 or Kir6.2 (encoded by KCNJ8 or KCNJ11) and the sulfonylurea receptor subunits SUR2A (encoded by ABCC9). These channels are closed under normoxic conditions, but open when intracellular ATP levels decline. All are expressed in ventricular myocardium, particularly in the epicardial layers.
Hypothesis: Mutations in KCNJ8 leading to a gain of function of KATP channel current (IK-ATP) underlie the development of Brugada (BrS) and early repolarization (ERS) syndromes.
Methods: Direct sequencing of all exons and intron borders of KCNJ8 and 9 other candidate genes was performed on 204 BrS and ERS probands and their family members. Whole-cell and inside-out patch clamp methods were used to study mutated channels expressed in HEK-293T cells.
Results: We identified the same missense mutation, p.S422L (c.1265 C>T) in KCNJ8, associated with 4 BrS and 1 ERS patients. This variant was absent in 764 alleles of healthy controls. Additional genetic variants included D601E-CACNB2b and G38S-KCNE1. Whole cell patch clamp studies showed a two-fold gain of function at 0 mV of glibenclamide-sensitive IK-ATP in S422L-KCNJ8 co-expressed with WT-SUR2A. Inside-out patch clamp evaluation yielded a significantly greater IC50 for ATP in the mutant channels (785.5 ±2 vs. 38.4±3 μM, n=6; p <0.01) pointing to incomplete closing of the IK-ATP channels under normoxic conditions. Patients with the D601E-CACNB2b and G38S-KCNE1 polymorphisms showed a longer QT/QTc than those without these variants, likely due to their effect to induce a persistent ICa-L or loss-of-function of IKs, respectively.
Conclusions: Our results provide evidence in support of the hypothesis that KCNJ8 is a susceptibility gene for both BrS (gene #8) and ERS (gene #1), both of which can be categorized as J wave syndromes. Our data also point to S422L as a hotspot mutation associated with these life threatening arrhythmia syndromes.
- © 2010 by American Heart Association, Inc.