CASQ2基因c.381C>T突变致儿茶酚胺敏感性多形性室性心动过速的分子机制

The Molecular Mechanism of c.381C>T Mutation in CASQ2 Gene Induced Catecholaminergic Polymorphic Ventricular Tachycardia

目的:对心电图上有U波,首诊怀疑长QTU综合征(LQTU)的两个家系进行基因筛查和功能检验,以期找到致病突变并结合临床信息作出疾病诊断。方法:筛查对象是2004~2005年来我院就诊的两个初诊为LQTU的家系L79和L104。诊断依据包括临床特征,如交感神经兴奋相关的晕厥,心电图记录到QT间期(或QU间期)延长及室性心动过速,且无器质性心脏病。记录先证者及其父母和一级亲属的病史、心电图和家族史,包括12导联静息心电图、24 h动态心电图和运动试验等。采用全外显子及Sanger测序法进行基因筛查。对发现的突变利用微小基因(minigene)技术进行功能验证。结果:两个家系中共有3例女性患者,皆为5岁左右首次发生晕厥。儿时心电图上有显著U波,随年龄增加U波幅度降低或消失。校正QT间期正常或临界值。基因筛查发现3例患者携带有CASQ2基因上的c.381C>T(p.Gly127=)纯合突变,父母杂合携带。其中L79家系先证者同时携带KCNQ1/c.921+1G>T杂合突变。Minigene实验证实,CASQ2/c.381C>T(p.Gly127=)突变虽未引起编码氨基酸改变,但其改变了3号外显子后面的生理性剪接位点并在380_381位点引入了一个新的剪切位点,致使其后41个核苷酸缺失,并在第128位置产生提前终止密码子。3例患者服用普萘洛尔或联合使用美西律,近3~15年无晕厥。结论:基因筛查及minigene功能验证结合家系临床表现,可确诊这3例患者为CASQ2/c.381C>T(p.Gly127=)纯合突变引起的儿茶酚胺敏感性多形性室性心动过速(CPVT)2型,L79先证者同时伴有KCNQ1/c.921+1G>T杂合突变所致的长QT综合征1型。本研究在中国CPVT患者中发现CASQ2基因编码区内的核苷酸同义变异可导致剪接突变效应。

Objectives:To define the genotype and phenotype in two pedigrees suspected as long QTU syndrome with obvious U wave on ECG.Methods:Gene screening was performed using whole exome sequencing and Sanger sequencing techniques.Functional verification was achieved by minigene assay for the detected mutation.Results:Two pedigrees(L79 and L104),admitted to our hospital from 2004 to 2005 suspected of long QTU syndrome with obvious U wave on ECG,were included in this study.There were 3 patients in two families.They all experienced the first syncope episodes at the age of 5 years.Obvious U wave was observed on the childhood ECG,and the amplitude of U wave decreased or disappeared as age increased.QTc was normal or borderline prolonged.Gene screening found that all three patients carried homozygous CASQ2/c.381C>T(p.Gly127=)mutation,and their parents carried heterozygous mutations.Among them,L79 proband simultaneously carried heterozygous KCNQ1/c.921+1G>T variant.Further minigene study confirmed a deletion of the last 41 nucleotides of exon 3 as a consequence of the creation of the cryptic splice donor site at position c.380_381 and the elimination of the physiological splice site of exon 3.This aberrant splicing would induce premature termination code(PTC)at position 128 in cardiac cells.There was no recurrent syncope in these 3 patients for the last 3 to 15 years under propranolol alone or in combination with mexiletine medication.Conclusions:Based on the results of gene screening and minigene functional verification and in combination with clinical manifestations,these 3 patients could be diagnosed as catecholaminergic polymorphic ventricular tachycardia(CPVT)caused by CASQ2/c.381C>T homozygous mutations.L79 proband also had type 1 long QT syndrome caused by KCNQ1/c.921+1G>T variant.This study also shows that a synonymous mutation c.381C>T(p.Gly127=)located in the coding domain of CASQ2 could result in aberrant splicing in Chinese CPVT patients.