Mutation detection of cardiac ion channel genes in sudden death cases

在一例年轻人猝死中，由于长QT综合征(LQT)是由多种离子通道基因突变引起的，我们建立了心脏传导系统表达的离子通道可能与猝死有关的工作理论。HERG、KVLQT和SCN5A突变导致LQT，以及Kir6.2、GIRK1、GIRK4和MAXK在8例猝死病例和100名健康对照中进行突变分析。根据GIRK4相关通道(I&lt；Kach&gt；)的功能，发现GIRK4内含子的C-T转换是猝死的唯一候选突变。这种转变被认为改变了剪接供体位置，导致在接下来的外显子中过早引入了终止密码子。预计该基因的mRNA量比通常的要长5个碱基对。RT-PCR检测从健康纯合子个体中回收的白细胞异位表达的mRNA，因为突变未能显示较长的mRNA，但这一结果并不意味着假定的剪接变异体不在脉冲传导系统中产生。除GIRK4突变外，仅有一小部分被截短的GIRK4基因以显性负效应导致I_lt；Kach&gt；通道功能受损。在这项研究中，并没有沿着基因的总长度寻找突变。将需要进一步筛查这些基因的突变。

In the sudden death of a young adult, which is unexplained by a morphorogical examination and is unexpected by past history, we contructed a working theory that ion channels expressed in cardiac conducting system may be involved in the sudden death because long QT syndrome (LQT) has been shown to be caused by mutations in various ion channel genes.HERG, KVLQT, and SCN5A of which mutations cause LQT, and Kir6.2, GIRK1, GIRK4, and MAXIK were analyzed for mutations in eight sudden death cases and 100 healthy controls. A C to T transition in an intron of GIRK4 was found to be the only candidate mutation for sudden death on the basis of the function of the GIRK4 associated channel (I_<KACh>). The transition was assumed to change the splice donor site, leading to premature introduction of stop codon in the following exon. The mRNA was expected to be 5 bp longer than usual one. RT-PCR of ectopically expressed mRNA in leucocytes recovered from a healthy individual homozygous for the mutation failed to show the longer mRNA but this result does not mean that the presumed splice variant is not produced in impulse' conducting system. Only a small fraction of the truncated GIRK4 must decrease the I_<KACh> channel by dominant negative effect, thus resulting in functional impairment of the I_<KACh> channel.In addition to the GIRK4 mutation, several polymorphic mutations were identified in the other channel genes but all of them were found to be neutral variants. In this study, mutation has not been searched for along the total length of the genes. Further screening for mutation of the genes will be required.