Biophysical properties of 9 KCNQ1 mutations associated with long-QT syndrome.
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.


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.
Yang
Tao
T
Department of Medicine and Pharmacology, Oates Institute for Experimental Therapeutics, Vanderbilt University School of Medicine, Nashville, Tenn, USA.
Chung
Seo-Kyung
SK
Zhang
Wei
W
Mullins
Jonathan G L
JG
McCulley
Caroline H
CH
Crawford
Jackie
J
MacCormick
Judith
J
Eddy
Carey-Anne
CA
Shelling
Andrew N
AN
French
John K
JK
Yang
Ping
P
Skinner
Jonathan R
JR
Roden
Dan M
DM
Rees
Mark I
MI
D000293:Adolescent; D000328:Adult; D000818:Animals; D001703:Biophysics; D016466:CHO Cells; D002648:Child; D006224:Cricetinae; D003412:Cricetulus; D016757:Death, Sudden, Cardiac; D005260:Female; D005838:Genotype; D006801:Humans; D051657:KCNQ1 Potassium Channel / Q000737:chemistry / Q000235:genetics* / Q000502:physiology*; D008133:Long QT Syndrome / Q000235:genetics* / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D016297:Mutagenesis, Site-Directed; D020125:Mutation, Missense; D018408:Patch-Clamp Techniques; D010375:Pedigree; D010641:Phenotype; D017434:Protein Structure, Tertiary; D013329:Structure-Activity Relationship; D014162:Transfection
D051657:KCNQ1 Potassium Channel; C496909:KCNQ1 protein, human