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

Biochim Biophys Acta. 2011 Nov;1812(11):1452-9. doi: 10.1016/j.bbadis.2011.07.011. Epub 2011 Jul 24.


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.

MeSH terms

  • Adolescent
  • Adult
  • Animals
  • Base Sequence
  • Computer Simulation
  • Exons / genetics*
  • Female
  • Heterozygote
  • Humans
  • Introns / genetics*
  • KCNQ1 Potassium Channel / genetics*
  • Long QT Syndrome / genetics*
  • Male
  • Molecular Sequence Data
  • Mutation / genetics*
  • Oocytes / metabolism
  • Pedigree
  • Phenotype
  • RNA Splicing / genetics*
  • RNA, Messenger / genetics
  • Reverse Transcriptase Polymerase Chain Reaction
  • Xenopus laevis / metabolism


  • KCNQ1 Potassium Channel
  • KCNQ1 protein, human
  • RNA, Messenger