Published online before print May 22, 2009, doi: 10.1161/CIRCEP.109.850149
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Original Articles |
Biophysical Properties of 9 KCNQ1 Mutations Associated With Long-QT Syndrome
From the Department of Medicine and Pharmacology (T.Y., W.Z., P.Y., D.M.R.), Oates Institute for Experimental Therapeutics, Vanderbilt University School of Medicine, Nashville, Tenn; Institute of Life Science (S.-K.C., J.G.L.M., M.I.R.), School of Medicine, Swansea University, Swansea, United Kingdom; the Department of Molecular Medicine and Pathology (C.H.M., J.K.F.), Faculty of Medical and Health Sciences, University of Auckland, Auckland, New Zealand; Cardiac Inherited Disease Group (J.C., J.M., C.-A.E., A.N.S., J.R.S., M.I.R.), Auckland Hospital, Auckland, New Zealand; the Department of Pediatric Cardiology (J.M., J.R.S.), Starship Hospital, Auckland, New Zealand; the Department of Obstetrics and Gynecology (C.-A.E., A.N.S.), Faculty of Medical and Health Sciences, University of Auckland, Auckland, New Zealand; the Department of Cardiology (J.K.F.) and South West Sydney Clinical School (UNSW) Liverpool Hospital, Sydney, Australia; and Institute of Medical Genetics (M.I.R.), School of Medicine, Cardiff University, Cardiff, United Kingdom.
Correspondence to Mark I. Rees, PhD, Institute of Life Science, School of Medicine, Swansea University, Singleton Park, Swansea SA2 8PP, United Kingdom. E-mail m.i.rees{at}swansea.ac.uk
Received January 14, 2009; accepted April 27, 2009.
Background— Inherited long-QT syndrome is characterized by prolonged QT interval on the ECG, syncope, and sudden death caused by ventricular arrhythmia. Causative mutations occur mostly in cardiac potassium and sodium channel subunit genes. Confidence in mutation pathogenicity is usually reached through family genotype-phenotype tracking, control population studies, molecular modeling, and phylogenetic alignments; however, biophysical testing offers a higher degree of validating evidence.
Methods and Results— By using in vitro electrophysiological testing of transfected mutant and wild-type long-QT syndrome constructs into Chinese hamster ovary cells, we investigated the biophysical properties of 9 KCNQ1 missense mutations (A46T, T265I, F269S, A302V, G316E, F339S, R360G, H455Y, and S546L) identified in a New Zealand-based long-QT syndrome screening program. We demonstrate through electrophysiology and molecular modeling that 7 of the missense mutations have profound pathological dominant-negative loss-of-function properties, confirming their likely disease-causing nature. This supports the use of these mutations in diagnostic family screening. Two mutations (A46T, T265I) show suggestive evidence of pathogenicity within the experimental limits of biophysical testing, indicating that these variants are disease-causing via delayed- or fast-activation kinetics. Further investigation of the A46T family has revealed an inconsistent cosegregation of the variant with the clinical phenotype.
Conclusions— Electrophysiological characterization should be used to validate long-QT syndrome pathogenicity of novel missense channelopathies. When such results are inconclusive, great care should be taken with genetic counseling and screening of such families, and alternative disease-causing mechanisms should be considered.
Key Words: long QT • mutations • arrhythmia • ion channels • sudden cardiac death
CLINICAL PERSPECTIVE
Guest editor for this article was Silvia Priori, MD, PhD.