长QT综合征一家系的遗传学定位研究

Genetic analysis of long QT syndrome in a Chinese family

目的 寻找中国人长QT综合征 (LQTS)的遗传易感位点 ,选择并确立LQTS患者症状前诊断的短串联重复序列 (shorttandemrepeats ,STR)和单核苷酸多态性 (singlenucleotidepolymorphism ,SNP) ,初步建立LQTS遗传学诊断方法。方法 采集一个LQTS家系四代共 37个成员 ,用聚合酶链反应 (PCR)方法扩增位于KCNQ1、HERG基因内的SNP(K5 46、K36 7、H489、和H5 6 4)和位于KCNQ1、HERG、和SCN5A基因邻近的STR (D11S132 3、D11S2 36 2、D11S1318、D7S6 36、D7S2 46 1、D7S182 4、D3S12 98、D3S176 7、D3S110 0、D4S15 6 4) ,所得产物经 6 %～ 10 %变性聚丙烯酰胺凝胶电泳后进行等位基因片段长度多态性分析或直接测序。结果 通过单倍体分析排除LQT1、LQT3、和LQT4位点 ,初步确定该LQTS家系的致病基因位于LQT2位点。HERG基因全部外显子的直接测序结果表明 7名患者均出现相同的HERG基因单碱基转换 (CGA2 5 87TGA) ,与之相对应的编码氨基酸由精氨酸 (Arg)突变为终止密码子TGA ,即R86 3X。结论 STR和SNP单倍体分析方法可以有效地区分正常及患病个体 ,确定LQTS致病基因的位点 ,可用于LQTS患者的症状前诊断。

Objective The long QT syndrome (LQTS) is a monogenic disorder that produces cardiac arrhythmias and can lead to sudden cardiac death. At least 6 loci and 5 known genes exist in which mutations have been shown to be responsible for the disease. But mutant screening in these genes including encoding and promoter region is still difficult. Method In a four-generation LQTS pedigree with 37 family members, every body underwent detail clinical and cardiovascular examination including a 12-lead ECG and a 24-hour Holter monitoring. The QT intervals were measured on ECG in lead Ⅱ or V 5 and corrected by heart rate (QTc) using Bazett's formula. Genomic DNA was extracted from blood samples by standard procedure. Microsatellite markers (D11S1323?D11S2362?D11S1318?D7S636?D7S2461?D7S1824?D3S1298?D3S1767?D3S1100?D4S1564) spanning the HERG?KCNQ1?SCN5A and LQT4 locus and SNP (K546?K367?H48 and H564) locating in the HERG and KCNQ1 were amplified, PCR products of the microsatellite markers were electrophoresised on 6% or 10% polyacrylamide gels including 7M urea and visualized by silver staining and PCR products of the SNP were sequenced. Alleles were analysed by two investigator independently. Result In this family, the result of haplotype analysis reveals that only LQT2 markers have the linkage with the disease, seven persons were found to be mutation carriers and two suspicious patients were excluded. In addition, a novel HERG nonsense mutation R863X was identified. Conclusion By haplotype analysis, we initially concluded that the disease gene of this pedigree is a LQT2-associated gene.