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(Circulation. 2007;115:368-376.)
© 2007 American Heart Association, Inc.

Pediatric Cardiology

Cardiac Sodium Channel Dysfunction in Sudden Infant Death Syndrome

Dao W. Wang, MD; Reshma R. Desai, MS; Lia Crotti, MD; Marianne Arnestad, MD, PhD; Roberto Insolia, BSc; Matteo Pedrazzini, BSc; Chiara Ferrandi, BSc; Ashild Vege, MD, PhD; Torleiv Rognum, MD, PhD; Peter J. Schwartz, MD; Alfred L. George, Jr, MD

From the Departments of Pharmacology (DW.W., A.L.G.) and Medicine (R.R.D., A.L.G.), Vanderbilt University, Nashville, Tenn; Molecular Cardiology Laboratory (L.C., R.I., M.P., C.F., P.J.S.,), IRCCS Policlinico S. Matteo, Pavia, Italy; Department of Cardiology (L.C., P.J.S.), University of Pavia and IRCCS Policlinico S. Matteo, Pavia, Italy; Institute of Forensic Medicine (M.A., A.V., T.R.), University of Oslo, Oslo, Norway.

Correspondence to Alfred L. George, Jr, Division of Genetic Medicine, 529 Light Hall, Vanderbilt University, 2215 Garland Ave, Nashville, TN 37232–0275. E-mail al.george{at}vanderbilt.edu

Received June 15, 2006; accepted September 1, 2006.

Background— Mutations in genes responsible for the congenital long-QT syndrome, especially SCN5A, have been identified in some cases of sudden infant death syndrome. In a large-scale collaborative genetic screen, several SCN5A variants were identified in a Norwegian sudden infant death syndrome cohort (n=201). We present functional characterization of 7 missense variants (S216L, R680H, T1304M, F1486L, V1951L, F2004L, and P2006A) and 1 in-frame deletion allele (delAL586-587) identified by these efforts.

Methods and Results— Whole-cell sodium currents were measured in tsA201 cells transiently transfected with recombinant wild-type or mutant SCN5A cDNA (hH1) coexpressed with the human ß1 subunit. All variants exhibited defects in the kinetics and voltage dependence of inactivation. Five variants (S216L, T1304M, F1486L, F2004L, and P2006A) exhibited significantly increased persistent sodium currents (range, 0.5% to 1.7% of peak current) typical of SCN5A mutations associated with long-QT syndrome. These same 5 variants also displayed significant depolarizing shifts in voltage dependence of inactivation (range, 5 to 14 mV) and faster recovery from inactivation, but F1486L uniquely exhibits a depolarizing shift in the conductance-voltage relationship. Three alleles (delAL586-587, R680H, and V1951L) exhibited increased persistent current only under conditions of internal acidosis (R680H) or when expressed in the context of a common splice variant (delQ1077), indicating that they have a latent dysfunctional phenotype.

Conclusions— Our present results greatly expand the spectrum of functionally characterized SCN5A variants associated with sudden infant death syndrome and provide further biophysical correlates of arrhythmia susceptibility in this syndrome.

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