遗传性长QT间期综合征KCNQ1基因的新突变

目的　研究遗传性长QT间期综合征 (longQTsyndrome ,LQTS)的临床特点并筛查KCNQ1基因突变。方法　首先按照国际公认的诊断标准 ,确立先证者 ,进行家系调查 ,共有 6个LQTS家系被纳入研究。另选 50名心电图正常且校正QT间期 (QTc)≤ 0 41s的健康人作为正常基因对照。分析先证者及家系成员的临床和心电图资料 ,采用聚合酶链反应 单链构像多态性 (polymerasechainreaction singlestrandconformationalpolymorphism ,PCR SSCP)方法 ,对KCNQ1基因编码区全部序列进行基因突变筛查。阳性结果行DNA测序以明确具体突变位点 ,并进行对照研究。结果　 6个家系中共有LQTS患儿 13例 ,男 5例 ,女 8例。其中 ,猝死 1例 ( 8% ) ;晕厥发作 10例 ( 77% ) ;无症状 2例 ( 15% ) ,分别在家系调查和基因筛查时被发现。共采集到 11例患儿的心电图 ,QT间期为 ( 0 460± 0 0 58)s ,QTc为 ( 0 516± 0 0 58)s。经基因检测发现KCNQ1基因上 2个新的致病性突变位点 3 56 3 57ΔQQ和 62 6 63 1ΔGSGGPP ,分别来自 2个家系。还发现 1个新的多态性位点P448R。此 3个位点均位于编码蛋白C 末端结构域。结论　该研究发现KCNQ1基因的 2个新缺失突变位点和 1个新的多态性位点 ,系国内外首次报道 ,丰富了LQTS离子通道突变的基因库资料

A novel KCNQ1 mutation in Chinese with congenital long QT syndrome

OBJECTIVE: Congenital long QT syndrome (LQTS) is an inherited disorder of cardiac repolarization characterized by prolongation of QT interval and polymorphic ventricular tachycardia torsade de pointes (TdP) in the electrocardiogram (ECG). Clinical symptoms include recurrent syncope, seizure or even sudden death. It is caused by mutations of at least seven genes, six of them encoding ion channels that determine the duration of ventricular action potentials. One of these genes, KCNQ1, encodes an alpha-subunit of cardiac slowly activated delayed rectifier potassium channel. Patients carrying mutations of KCNQ1 are named as LQT1, which accounts for 42% of patients with LQTS. This study sought to analyze the clinical data of Chinese with LQTS and to screen for the mutations of KCNQ1. METHODS: The universally accepted phenotypic criteria of LQTS was used for identification of probands. There were six families with LQTS. They were enrolled in this study. Clinical and ECG data of each family member were recorded. Genomic DNA was prepared from peripheral blood lymphocytes. Polymerase chain reaction-single strand conformation polymorphism analysis was used to screen for mutations throughout the whole coding region of KCNQ1 and DNA sequencing was performed to determine the exact mutation site. RESULTS: There were totally 13 patients in the six LQTS families. Five were male and eight female. One suffered from sudden death, 10 had syncope and 2 were asymptomatic. Eleven of the 13 patients had ECG data. Their QT and QTc (mean +/- SD) were (0.460 +/- 0.058) s and (0.516 +/- 0.058) s, respectively. TdP was observed in 3 patients (27%) during the syncope attack. By PCR-SSCP analysis, two novel KCNQ1 deletion mutations 356-357 Delta QQ and 626-631 Delta GSGGPP were identified in 7 patients of 2 families. None of 50 normal individuals carried these mutations, indicating these two mutations were likely to cause the disease. In addition, P448R was found in one affected and some unaffected members in other two families and in 7 of 50 (14%) normal individuals, indicating that this might be a polymorphism. All the three mutations located in C-terminal domain of KCNQ1 protein. CONCLUSIONS: Two novel deletion mutations and one novel polymorphism of KCNQ1 gene were identified among 6 Chinese families with LQTS.