Abstract 15531: FGF12 is a Novel Brugada Syndrome Locus
Brugada syndrome (BrS) is a potentially lethal heritable arrhythmia syndrome that can result from loss-of-function mutations in Na+ (NaV1.5) or Ca2+ (CaV1.2) channels. Recently, we discovered that fibroblast growth factor (FGF) homologous factors (FHFs, FGF11-14) are intracellular modulators of these cardiac channels, with FGF12 being the most highly expressed FHF in human ventricle. Using a candidate gene approach, comprehensive open reading frame and splice site mutational analysis of FGF12 was performed on 102 unrelated BrS patients. One putative pathogenic mutation, Q7R-FGF12, was identified in a single unrelated BrS patient that was absent in at least 2000 internal reference alleles and over 5000 publicly available exomes. To avoid possible misleading results from heterologous expression systems that lack the milieu of a cardiomyocyte, we examined the effect of the putative FGF12 BrS-associated variant on Na+ and/or Ca2+ channel function in adult rat cardiomyocytes. Since rat cardiomyocytes express FGF13 instead of FGF12, we knocked down the endogenous FGF13 and performed functional studies expressing either wild-type (WT) or Q7R human FGF12 by adenoviral transduction. Voltage-clamp results demonstrated that WT-FGF12 successfully rescued the reduction in Na+ channel current in cardiomyocytes after FGF13 knockdown, suggesting that human FGF12 can replace the endogenous rat FGF13. In contrast, the Q7R-FGF12 mutant could not. Both WT- and Q7R-FGF12 were able to rescue reduction in Ca2+ channel current seen after FGF13 knockdown, with the mutant producing a slight increase in Ca2+ current above baseline. Action potential recordings from Q7R-expressing cardiomyocytes showed decreased amplitude and increased half-width, consistent with the effects observed on the two currents. Co-immunoprecipitation and isothermal titration calorimetry assays demonstrated that Q7R-FGF12 decreased binding affinity between FGF12 and its known interaction site on the NaV1.5 C-terminus. Thus, using molecular interrogation and a novel cardiomyocyte expression system, our data provides the first evidence that FGF12 is a new locus for BrS and the Q7R mutation precipitates a loss-of-function in Na+ currents.
- © 2013 by American Heart Association, Inc.