Phamacogenomic studies for the genetic basis for lethal arrhythmias

对120例正常人、30例先天性长QT综合征(cLQTS；n=30)、4例获得性长QT综合征(aLQTS；n=4)、30例无症状Brugada综合征(ABS；n=30)、37例症状性Brugada综合征(SBS；n=37)、2例进行性心脏传导障碍(PCCD；n=2)和2例房性停搏(AS；n=2)患者的基因组DNA进行了基因筛查。心脏钠通道基因(SCN5A)、cLQTS(2/30)、aLQTS(1/4)、ABS(1/30)、SBS(5/37)、PCCD(1/2)和AS(1/2)有9个明显的突变。利用哺乳动物培养细胞TSA-201，用定点突变和异源表达系统检测8个SCN5A突变的生物物理异常。通过瞬时转染这些突变的钠通道来记录全细胞钠电流。3个负责cLQTS和aLQTS的突变通道表现出持续的钠电流，这是其他LQT3突变通道的特征。SBS的5个突变通道中有2个突变通道和AS突变通道无明显电流。导致ABS的突变是SCN5A相同外显子上的双突变，表现出BS的功能丧失特征。我们在SCN5A中发现了两个新的单核苷酸多态(SNP)。V1951L和L1988R。TaqMan法检测的等位基因频率在正常组和Brugada综合征组之间无显著差异。这些SNP对氟卡胺的敏感性与野生型钠通道几乎相同，这表明这些SNP不太可能导致对钠通道阻滞剂敏感性的差异。在ABS病例中发现的双突变是导致ABS的第一个SCN5A突变(Yokoi等人)。心跳节律2005)。导致强直性脊柱炎的突变是迄今为止报道的第三个SCN5A突变。在这种情况下，我们在连接蛋白40中发现了伴随的SNP，现在正在研究这种房性心律失常的发病机制。

Genetic screening was performed in the genomic DNAs from normal volunteers (n=120), congenital long QT syndrome (cLQTS ; n=30), acquired long QT syndrome (aLQTS ; n=4), asymptomatic Brugada syndrome (aBS ; n=30), symptomatic Brugada syndrome (sBS ; n=37), progressive cardiac conduction disturbance (PCCD ; n=2), and atrial standstill (AS ; n=2).We found a cardiac possatium channel gene KCNH2 mutation in cLQTS. Nine distinct mutations were found in cardiac Na channels genes (SCN5A) ; cLQTS(2/30), aLQTS(1/4), aBS(1/30), sBS(5/37), PCCD(1/2), and AS(1/2). Biophysical abnormalities of the eight SCN5A mutations were determined by site-directed mutagenesis and heterologous expression system using mammalian cultured cell tsA-201. Whole cell Na current were recorded by transient transfection of these mutant Na channels. 3 mutant channels responsible for cLQTS and aLQTS showed persistent Na current that is characteristic for other LQT3 mutant channels. 2 mutant channels out of 5 mutation of sBS and the AS mutant channel showed no observable current. The mutation responsible for aBS was a double mutation at the same exon of SCN5A, and showed loss-of function properties characteristic for BS.We have identified two novel single nucleotide polymorphisms (SNP) in SCN5A. V1951L and L1988R. Allele frequencies determined by TaqMan PCR strategies was not significantly difference between normal group and Brugada syndrome group. Flecainide sensitivities of these SNPs were nearly identical to wild type Na channel, suggesting that these SNPs are unlikely to underlie differences in the sensitivities to Na channel blockers.The double mutation identified in an aBS case is the first SCN5A mutation responsible for aBS (Yokoi et al. Heart Rhythm 2005). The mutation responsible for AS was the third SCN5A mutation reported so far. We found a concomitant SNP in the connexin 40 in this case, and now investigating the pathogenesis of atria-specific nature of this arrhythmia.