N- and C-terminal KCNE1 mutations cause distinct phenotypes of long QT syndrome.

BACKGROUND: Long QT syndromes (LQTS) are inherited diseases involving mutations to genes encoding a number of cardiac ion channels and a membrane adaptor protein. The MinK protein is a cardiac K-channel accessory subunit encoded by the KCNE1 gene, mutations of which are associated with the LQT5 form of LQTS.
OBJECTIVE: The purpose of this study was to search for the KCNE1 mutations and clarify the function of those mutations.
METHODS: We conducted a genetic screen of KCNE1 mutations in 151 Japanese LQTS patients using the denaturing high-performance liquid chromatography-WAVE system and direct sequencing. In two LQTS patients, we identified two KCNE1 missense mutations, located in the MinK N- and C-terminal domains. The functional effects of these mutations were examined by heterologous coexpression with KCNQ1 and KCNH2.
RESULTS: One mutation, which was identified in a 67-year-old woman, A8V, was novel. Her electrocardiogram (ECG) revealed marked bradycardia and QT interval prolongation. Another mutation, R98W, was identified in a 19-year-old woman. She experienced syncope followed by palpitation in exercise. At rest, her ECG showed bradycardia with mild QT prolongation, which became more prominent during exercise. In electrophysiological analyses, R98W produced reduced I(Ks) currents with a positive shift in the half activation voltages. In addition, when the A8V mutation was coexpressed with KCNH2, this reduced current magnitude, which is suggestive of a modifier effect by the A8V KCNE1 mutation on I(Kr).
CONCLUSION: KCNE1 mutations may be associated with mild LQTS phenotypes, and KCNE1 gene screening is of clinical importance for asymptomatic and mild LQTS patients.