Clinical Science (2003) 104, 377-382 - M. Yamaguchi and others - Characterization of an F193L mutation in the KCNQ1 gene

Clinical Science (2003) 104, (377–382) (Printed in Great Britain)

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Clinical and electrophysiological characterization of a novel mutation (F193L) in the KCNQ1 gene associated with long QT syndrome

Masato YAMAGUCHI*,Masami SHIMIZU*,Hidekazu INO*,Hidenobu TERAI*,Kenshi HAYASHI*,Hiroshi MABUCHI*,Naoto HOSHI† andHaruhiro HIGASHIDA†

*Molecular Genetics of Cardiovascular Disorders, Division of Cardiovascular Medicine, Graduate School of Medical Science, Kanazawa University, Takara-machi 13-1, Kanazawa 920-8641, Japan, and †Biophysical Genetics, Division of Neuroscience, Graduate School of Medical Science, Kanazawa University, Takara-machi 13-1, Kanazawa 920-8641, Japan

Abbreviations: ECG, electrocardiogram; I_Ks, slow component of the delayed rectifier K⁺ current; LQTS, long QT syndrome; F193L, Phe193Leu; JLNS, Jervell and Lange-Nielsen syndrome; QTc, QT interval corrected for heart rate; RFLP, restriction fragment length polymorphism; SSCP, single-strand conformational polymorphism; WT, wild-type.

KCNQ1 is a gene encoding an a subunit of voltage-gated cardiac K⁺ channels, with properties similar to the slowly activating delayed rectifier K⁺ current, and one of the genes causing long QT syndrome (LQTS). However, genotype–phenotype correlations of the KCNQ1 gene mutations are not fully understood. The aims of this study were to identify a mutation in the KCNQ1 gene in patients with LQTS, and to characterize the clinical manifestations and electrophysiological properties of the mutation. We screened and identified mutations by PCR, single-strand conformational polymorphism analysis and DNA sequencing. We identified a novel mutation [Phe193Leu (F193L)] in the KCNQ1 gene in one family with LQTS. The patients with this mutation showed a mildly affected phenotype. The proband was a 17-year-old girl who had a prolonged QT interval. Her elder brother, father and paternal grandmother also had the mutation. None of them had any history of syncope. Sudden death was not found in this family. Next, we studied the electrophysiological characteristics of the F193L mutation in the KCNQ1 gene using the expression system in Xenopus oocytes and the two-microelectrode voltage-clamp technique. Co-expression of F193L KCNQ1 with the K⁺ channel minK suppressed peak (by 23.3%) and tail (by 38.2%) currents compared with those obtained by the combination of wild-type (WT) KCNQ1 and minK. Time constants of current activation in F193L KCNQ1 and F193L KCNQ1+minK were significantly slower than those of WT KCNQ1 and WT KCNQ1+minK. This electrophysiological study indicates that F193L causes less severe KCNQ1 current suppression, and thereby this mutation may result in a mildly affected phenotype.