1/2. Trafficking-competent and trafficking-defective KCNJ2 mutations in andersen syndrome.Mutations in KCNJ2, the gene encoding the human inward rectifier potassium channel Kir2.1, have been identified in andersen syndrome (or Andersen-Tawil syndrome), an inherited disorder characterized by periodic paralysis, cardiac arrhythmias, and dysmorphic features. We identified and characterized two novel KCNJ2 mutations (c.220A>G/p.T74A and c.443G>C/p.G144A) associated with andersen syndrome. Heterologous expression of a recombinant wild type human KCNJ2 cDNA (WT-KCNJ2) in HEK-293 cells results in robust inward rectifying currents, but we did not observe measurable currents from cells expressing either mutant. cells co-transfected with WT-KCNJ2 and either mutant exhibited substantially lower whole-cell current amplitude consistent with a dominant-negative suppression of WT-KCNJ2 by the mutant channels. Both p.T74A and p.G144A exhibit robust plasma membrane expression, but a third previously reported allele (p.C101R) exhibited impaired trafficking. Our results demonstrate functional consequences of two novel trafficking-competent KCNJ2 mutations associated with andersen syndrome and expand our knowledge of allelic diversity in this disease. ( info) |
2/2. Functional and clinical characterization of a mutation in KCNJ2 associated with Andersen-Tawil syndrome.BACKGROUND: Andersen-Tawil syndrome (ATS) is a rare inherited disorder, characterised by periodic paralysis, cardiac dysarrhythmias, and dysmorphic features, and is caused by mutations in the gene KCNJ2, which encodes the inward rectifier potassium channel, Kir2.1. This study sought to analyse KCNJ2 in patients with familial ATS and to determine the functional characteristics of the mutated gene. methods AND RESULTS: We screened a family with inherited ATS for the mutation in KCNJ2, using direct dna sequencing. A missense mutation (T75R) of Kir2.1, located in the highly conserved cytoplasmic N-terminal domain, was identified in three affected members of this family. Using the xenopus oocyte expression system and whole cell voltage clamp analyses, we found that the T75R mutant was non-functional and possessed a strong dominant negative effect when co-expressed with the same amount of wild type Kir2.1. Transgenic (Tg) mice expressing the mutated form of Kir2.1 in the heart had prolonged QTc intervals compared with mice expressing the wild type protein. Ventricular tachyarrhythmias were observed in 5 of 14 T75R-Tg mice compared with 1 of 7 Wt-Tg and none of 6 non-transgenic littermates. In three of five T75R-Tg mice with ventricular tachycardia, their ECG disclosed bidirectional tachycardia as in our proband. CONCLUSIONS: The in vitro studies revealed that the T75R mutant of Kir2.1 had a strong dominant negative effect in the xenopus oocyte expression system. It still preserved the ability to co-assemble and traffic to the cell membrane in mammalian cells. For in vivo studies, the T75R-Tg mice had bidirectional ventricular tachycardia after induction and longer QT intervals. ( info) |