Abstract 16896: A Gain-of-Function Mutation in the Membrane-Associated Guanylate Kinase Protein SAP97 is Associated with Brugada Syndrome
Introduction: Brugada syndrome (BrS) is a potentially lethal heritable arrhythmia syndrome for which mutations have been identified in 12 BrS-susceptibility genes that account for only 20-30% of the disease. DLG1 encodes the protein synapse-associated protein 97 (SAP97), a protein belonging to the membrane-associated guanylate kinase (MAGUK) family of proteins that are important for localization and organization of ion channels. SAP97 interacts with and modulates cardiac Kv4.3 channels that account for a large part of the transient outward potassium current (Ito). Given the prominent role of Ito in the pathogenesis of BrS, we hypothesized that mutations in DLG1-encoded SAP97 may modulate Ito function and confer pathogenic susceptibility for BrS.
Methods: Using PCR, DHPLC, and direct DNA sequencing, comprehensive open reading frame analysis and splice site mutational analysis of DLG1 was performed in 46 unrelated patients with clinically diagnosed BrS (type 1 Brugada ECG pattern plus personal/family history of a cardiac event). DNA from 990 healthy individuals was examined to determine the allelic frequency of all identified non-synonymous variants. The putative SAP97 BrS-associated mutation was engineered via site directed mutagenesis and functional studies of both wild-type and mutant SAP97 were carried out using the whole cell patch clamp technique.
Results: One putative pathogenic mutation, absent in at least 1900 reference alleles, was identified in a single unrelated clinically diagnosed BrS case. The missense mutation, M861T, was found in a 60-year-old male with drug-induced ST-segment elevation in V1-V3, and a positive family history of sudden cardiac death. Co-expression of SAP97-M861T plus Kv4.3-WT in CHO cells resulted in a marked 70.4% increase in Ito peak current density at +40mV compared to SAP97-WT plus Kv4.3-WT (n = 18, p <0.05). No statistical differences in the activation/inactivation kinetics were observed between SAP97-M861T and SAP97-WT on Kv4.3-WT channels.
Conclusions: This study provides the first molecular and functional evidence implicating a gain-of-function mutation in the SAP97 protein that results in a biogenic increase in Ito/Kv4.3 current as a predisposing arrhythmic mechanism in the pathogenesis of BrS.
- © 2012 by American Heart Association, Inc.