KCNQ1 MUTATION CAUSING DOMINANT-NEGATIVESUPPRESSION DUE TO DEFECTIVE CHANNELTRAFFICKING UNDERLIES CARDIAC ARREST IN APATIENT WITH LONG QT SYNDROME

摘要

Long-QT syndrome is caused by mutations in 7 defined genes that mostly encode K+ and Na+ channels, and the underlying mechanisms are variable among different gene mutations. A 13-year-old girl with a history of cardiopulmonary arrest was referred to our institute for genetic analysis. Her QT interval at rest was prolonged (QTc=O.52sec) and it further prolonged with exercise (maximum QTc=0.62sec).PCR-SSCP and DNA sequence analysis identified a novel frameshift mutation Alal78fs/105 in KCNQ1, resulting in premature stop codon that eliminates the portions of S3-S6 and C-tenninus of the channel. We examined electrophysiological properties using heterologous expression system in COS-7 cells. Whole-cell patch-clamp technique demonstrated that the WT-KCNQ1 with KCNE1 produced normal IKs current, while no current was observed in cells expressing A178fs/105 mutant and KCNE1. Co-expression of WT- and A178fe/105-KCNQl along with KCNE1 suppressed the current with a dominant-negative manner. Next we examined the subcellular localization of WT and/or A178fs/105 mutant channel using confocal laser microscopy which revealed trafficking deficiency of A178fs/105 mutant. Co-expression of GFP-tagged WT- with A178fs/105-KCNQ1 also induced the intracellular retention of the channel protein. We conclude that the A178fs/105 mutation causing dominant-negative suppression due to trafficking defect is an underlying mechanism for fatal arrhythmias of this patient.