PO-04-166 DISTURBED PH CONTROL BY A NOVEL SLC4A3 VARIANT IDENTIFIED IN A SHORT QT SYNDROME FAMILY WITH A KCNH2 VARIANT

Abstract

Short QT syndrome (SQTS) is one of the inherited primary arrhythmia syndromes and characterized by shortened QT intervals leading to ventricular fibrillation (VF) and sudden cardiac death, especially in young people. The major cause of SQTS is pathogenic variants in KCNH2 encoding Kv11.1 which produce IKr. Recently, a novel variant in SLC4A3 encoding the anion exchanger (AE3) has been identified in two SQTS families. However, the pathogenesis of SQTS caused by SLC4A3 variants in the presence of a KCNH2 variant have not been elucidated yet. We aimed to elucidate the functional change of a novel SLC4A3 variant in the interaction with a KCNH2 variant. We performed targeted gene sequencing (TGS) and whole exome sequencing (WES) in SQTS patients. Electrophysiological characteristics of the KCNH2 variant were analyzed using HEK293 cells by patch-clamp methods. We constructed stable HEK293 cell lines expressing SLC4A3 with or without the variant and measured intracellular pH (pHi) by ratiometric pH indicator, BCECF-AM. Using the stable cell lines, we transfected KCNH2 (WT or the variant), KCNQ1 and KCNJ2 and measured IKr, IKs and IK1. We identified a KCNH2 variant, c.280 c>t, p.H70Y by TGS in a 25-year-old man who suffered VF at night and was diagnosed with SQTS after resuscitation. We first performed electrophysiological analysis of KCNH2-H70Y alone, however, the variant affected a little of Ikr properties. Therefore, we performed WES in the proband and his family, and a novel SLC4A3 variant, c.1059 c>a, p.N353K was identified. Both variants were co-segregated in his family with short QT intervals. In the live cell imaging analysis, cells expressing SLC4A3-N353K showed significantly slower pHi alternations than those with WT (figure A), reflecting the loss-of-function effect of exchange kinetics in mutant AE3. In the electrophysiological analysis using stable cell lines expressing SLC4A3, IKs and IK1 did not show any changes in channel properties regardless the presence of SLC4A3-N353K. However, IKr with H70Y showed significantly slow deactivation time constant in the cells expressing SLC4A3-N353K (Figure B and C), which means the gain-of-function effect on Kv11.1. SLC4A3-N353K showed slower alteration of pHi, a loss-of-function effect on AE3. With the expression of SLC4A3-N353K,KCNH2-H70Y decelerated the deactivation kinetics of Ikr, which may lead to shortening of QT intervals in our patient.