Molecular Medicine of long QT syndrome

对长QT综合征患者进行了编码心脏离子通道的4个长QT相关基因KCNQ 1（LQT 1）、KCNH 2（LQT 2）、KCNE 1（LQT 5）、KCNE 2（LQT 6）的基因突变筛查。还检查了获得性长QT患者。遗传分析方案由机构伦理委员会批准，并根据其指导原则进行。所有受试者均事先知情同意进行基因分析。通过常规方法从白细胞核中分离基因组DNA。采用聚合酶链反应/单链构象多态性（PCR-SSCP）分析进行突变筛查。PCR产物用甲酰胺热变性，并施加到用SYBR绿色II（Moleculai Probes）染色的13%聚丙烯酰胺凝胶上。测序在ABI测序仪（PRISM 310，PE Applied Biosystems）上进行。在9个家系中发现7个KCNQ 1突变，6个家系中发现6个KCNH 2突变，3个家系中发现3个SCN 5A突变。此外，在3个Brugada综合征家系中发现3个SCN 5A突变。最近，编码心脏内向整流K通道的KCNJ 2突变已被证明可导致安德森综合征，其特征为周期性麻痹、心律失常和畸形特征。我们在两个非典型Andersen综合征家系中发现两个KCNJ 2基因突变。在KCNQ 1中检测到两个单核苷酸多态性，其中一个是G643 S，而另一个是P448 R，这两个单核苷酸多态性是最常见的病理性突变。通过定点突变和转染COS 7细胞进行功能检测。后一种突变被发现导致外向IKs电流的小但显著的减少。

Genetic screening for mutations was conducted in patients with long QT syndrome for four long QT-related genes coding cardiac ion channels, KCNQ1 (LQT1), KCNH2 (LQT2), KCNE1 (LQT5), KCNE2 (LQT6). Acquired long QT patients were also examined. The protocol for genetic analysis was approved by the institutional ethics committee and performed under its guidelines. All subjects gave informed prior consent for gene analysis. Genomic DNA was isolated from leukocyte nuclei by conventional methods. Screening for mutations was performed by polymerase chain reaction/single-strand conformation polymorphism (PCR-SSCP) analysis. PCR products were heat-denatured with formamide and applied to a 13 % polyacrylamide gel stained with SYBR Green II (Moleculai Probes). Sequencing was on ABI sequencers (PRISM 310, PE Applied Biosystems). We found 7 KCNQ1 mutations in 9 families, 6 KCNH2 mutations in 6 families, 3 SCN5A mutations in 3 families. In addition, 3 SCN5A mutations were found in 3 families affected by Brugada syndrome. More recently, mutations in KCNJ2 coding cardiac inward rectifier K channel has been shown to cause Andersen syndrome, characterized by periodic paralysis, cardiac arrhythmia, and dysmorphic features. We found two mutations in KCNJ2 gene in two families with atypical Andersen syndrome. All the affected patients also showed a marked prolongation of QT interval, indicating that the mutation in KCNJ2 is another cause of long QT syndrome, Two single nucleotide polymorphism were detected in KCNQ1, in which the pathological mutations are most frequently identified, and one them, G643S, appeared to correspond to the phenotypic QT iprolongation, but not the other, P448R. Funetional assay of these mutants were conducted by using site-directed mutagenesis and transfection in COS7 cells. The latter mutation was found to cause small but significant reduction of outward IKs currents.