Functional Effects of KCNE3 Mutation and Its Role in the Development of Brugada Syndrome

Background-The Brugada syndrome, ail inherited syndrome associated with a high incidence of sudden cardiac arrest, has been linked to mutations in 4 different genes, leading to a loss of function in sodium and calcium channel activity. Although the transient outward current (I-to) is thought to play a prominent role in the expression of the syndrome, mutations in I-to-related genes have not been identified as yet. Methods and Results-One hundred five probands with the Brugada syndrome were screened for ion channel gene mutations using single-strand conformation polymorphism electrophoresis and direct sequencing. A missense mutation (R99H) in KCNE3 (MiRP2) was detected in 1 proband. The R99H mutation was found 4/4 phenotype-positive and 0/3 phenotype-negative family members. Chinese hamster ovary-K1 cells were cotransfected using wild-type (WT) or mutant KCNE3 and either WT KCND3 or KCNQ1. Whole-cell patch clamp studies were performed after 48 hours. Interactions between Kv4.3 and KCNE3 were analyzed in coimmunoprecipitation experiments in human atrial samples. Cotransfection of R99H-KCNE3 with KCNQ1 produced no alteration in tail current magnitude or kinetics. However, cotransfection of R99H KCNE3 with KCND3 resulted in a significant increase in the I-to intensity compared with WT KCNF-3+KCND3. Using tissues isolated from the left atrial appendages of human hearts, we also demonstrate that Kv4.3 and KCNE3 can be coimmunoprecipitated. Conclusions-These results provide definitive evidence for a functional role of KCNE3 in the modulation of I-to in the human heart and suggest that mutations in KCNE3 can underlie the development of the Brugada syndrome. (Circ Arrhythmia Electrophysiol. 2008;1:209-218.)