Gain of function in IKs, secondary to a mutation in KCNE5 associated with atrial fibrillation

BACKGROUND Atria( fibrillation (AF) is the most common clinical arrhythmia and a major cause of cardiovascular morbidity and mortality. Among the gene defects previously associated with AF is a gain of function of the slowly activating delayed rectifier potassium current I,,, secondary to mutations in KCNQ1. Coexpression of KCNE5, the gene encoding the MiRP4 P-subunit, has been shown to reduce I-Ks. OBJECTIVE The purpose of this study was to test the hypothesis that mutations in KCNE5 are associated with AF in a Large cohort of patients with AF. METHODS One-hundred fifty-eight patients with AF were screened for mutations in the coding region of KCNE5. RESULTS A missense mutation involving substitution of a phenylalanine for leucine at position 65 (L65F) was identified in one patient. This patient did not have a history of familial AF, and neither KCNQ1 nor KCNE2 mutations were found. Transient transfection of Chinese hamster ovary (CHO) cells expressing I-Ks (KCNQ1+KCNE1) with KCNE5 suppressed the developing and tail currents of I, in a concentration-dependent manner. Transient transfection with KCNE5-L65F failed to suppress I-Ks yielding a current indistinguishable from that recorded in the absence of KCNE5. Developing currents recorded during a test pulse to +60 mV and tail currents recorded upon repolarization to -40 mV both showed a significant concentration-dependent gain of function in I-Ks with expression of KCNE5-L65F vs KCNE5-WT. CONCLUSION The results of this study suggest that a missense mutation in KCNE5 may be associated with nonfamilial or acquired forms of AF. The arrhythmogenic mechanism most likely is a gain of function of I-Ks.