© 2002 by European Society of Cardiology
Copyright © 2002, European Society of Cardiology
A novel SCN5A arrhythmia mutation, M1766L, with expression defect rescued by mexiletine
aDepartments of Medicine and Physiology, University of Wisconsin, Madison, WI, USA
bDepartments of Internal Medicine, Pediatrics, and Molecular Pharmacology, Long QT Syndrome Clinic, Guggenheim 501, Mayo Clinic, Rochester, MN 55905, USA
cPediatric Cardiology Associates, Tampa Bay, FL, USA
* Corresponding author. Tel.: +1-507-284-0101; fax: +1-507-284-3757 ackerman.michael{at}mayo.edu
Objective: Mutations in the cardiac sodium channel gene, SCN5A, cause congenital long QT syndrome (LQT3), Brugada syndrome, idiopathic ventricular fibrillation, and conduction disease by distinct cellular and clinical electrophysiological phenotypes. Methods: Postmortem molecular analysis of SCN5A was conducted on an infant who presented shortly after birth with self-terminating torsades de pointes. The infant was treated with lidocaine, propranolol, and mexiletine and was stable for 16 months manifesting only a prolonged QT interval. The infant collapsed suddenly following presumed viral gastroenteritis, was found in 2:1 AV block, and was subsequently declared brain dead. Genomic DNA was subjected to SCN5A mutational analyses and DNA sequencing revealing a novel, spontaneous germline missense mutation, M1766L. The M1766L mutation was engineered into the hH1a clone by site-directed mutagenesis, transfected into embryonic kidney cells (HEK-293), and studied by voltage clamp. Results: The M1766L mutation caused a significant decrease in the sodium channel expression. Co-expression with β1 subunit, incubation at low temperature, and most effectively incubation with mexiletine partially ‘rescued’ the defective expression. In addition to this pronounced loss of function, M1766L also showed a 10-fold increase in the persistent late sodium current. Conclusions: These findings suggest that M1766L–SCN5A channel dysfunction may contribute to the basis of lethal arrhythmias, displays an overlapping electrophysiological phenotype, and represents the first sodium channelopathy rescued by drug.
KEYWORDS hH1a, NaV1.5 clone used in this study; INa, sodium current; M1766L, mutated hH1a channel containing a leucine at position 1766 instead of the normal methionine residue; NaV1.5, nomenclature for the channel protein product of SCN5A; SCN5A, official gene designation for the cardiac sodium channel gene residing on chromosome 3p21; WT, ‘wild-type’ Na channel
1 C.R.V. and M.J.A. are co-equal first authors.
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