Identification and functional characterization of KCNQ1 mutations around the exon 7-intron 7 junction affecting the splicing process

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Abstract

Background. KCNQ1 gene encodes the delayed rectifier K + channel in cardiac muscle, and its mutations cause long QT syndrome type 1 (LQT1). Especially exercise-related cardiac events predominate in LQT1. We previously reported that a KCNQ1 splicing mutation displays LQT1 phenotypes. Methods and results. We identified novel mutation at the third base of intron 7 (IVS7 +3A>G) in exercise-induced LQT1 patients. Minigene assay in COS7 cells and RT-PCR analysis of patients' lymphocytes demonstrated the presence of exon 7-deficient mRNA in IVS7 +3A>G, as well as c.1032G>A, but not in c.1022C>T. Real-time RT-PCR demonstrated that both IVS7 +3A>G and c.1032G>A carrier expressed significant amounts of exon-skipping mRNAs (18.8% and 44.8% of total KCNQ1 mRNA). Current recordings from Xenopus oocytes injected cRNA by simulating its ratios of exon skipping displayed a significant reduction in currents to 64.8±4.5% for IVS7 +3A>G and to 41.4±9.5% for c.1032G>A carrier, respectively, compared to the condition without splicing error. Computer simulation incorporating these quantitative results revealed the pronounced QT prolongation under beta-adrenergic stimulation in IVS7 +3A>G carrier model. Conclusion. Here we report a novel splicing mutation IVS7 +3A>G, identified in a family with mild form LQT1 phenotypes, and examined functional outcome in comparison with three other variants around the exon 7-intron 7 junction. In addition to c.1032G>A mutation, IVS7 +3A>G generates exon-skipping mRNAs, and thereby causing LQT1 phenotype. The severity of clinical phenotypes appeared to differ between the two splicing-related mutations and to result from the amount of resultant mRNAs and their functional consequences. © 2011 Elsevier B.V.

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Tsuji-Wakisaka, K., Akao, M., Ishii, T. M., Ashihara, T., Makiyama, T., Ohno, S., … Horie, M. (2011). Identification and functional characterization of KCNQ1 mutations around the exon 7-intron 7 junction affecting the splicing process. Biochimica et Biophysica Acta - Molecular Basis of Disease, 1812(11), 1452–1459. https://doi.org/10.1016/j.bbadis.2011.07.011

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