Molecular Medicine of long QT syndrome

点击翻译按钮获取中文摘要

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.