Genotype-Phenotype Discordance in Long QT Syndrome

描述(申请人提供)：心脏性猝死(SCD)是一种灾难性事件，每年在美国造成多达45万人死亡。在SCD高危患者中，有遗传性心律失常的患者。长QT间期综合征(LQTS)是一组遗传性心律失常，可导致心肌膜电流缺陷。其直接结果是，LQTS与心电图QT间期延长、室性心律失常和SCD发生率增加有关。在LQTS2中，已在编码HERG的KCNH2基因中发现了200多个错义突变，其中绝大多数被认为具有蛋白质加工和运输缺陷，导致钾电流急剧减少。然而，正如在许多常染色体显性遗传性心脏通道病中常见的观察到的那样，这些患者的遗传模式和临床表型是复杂的，通常表现为不完全外显，致病突变携带者没有症状。这种可变的临床表现的原因还不是很清楚，但在目前的研究方案中，我们将通过检验修饰基因对可变的临床表现的影响这一假设来研究这个问题。我们在MetroHealth和凯斯西储大学的多学科小组已经在临床和体外研究了一个携带HERG突变R752W的‘克利夫兰’LQT2大家族。在研究的101名家庭成员中，有26人携带Herg R752W突变。然而，有症状的LQTS只出现在5个受遗传影响的家庭成员中，因此说明该疾病的不完全外显性。我们假设疾病修饰基因的存在可以解释在这个LQT2家族中观察到的基因型-表型不一致。在这项研究中，我们将通过外显子组测序和从患者诱导的多能干细胞(IPS)分化的心肌细胞来阐明LQT2家族不完全外膜的机制。我们假设患者来源的iPS分化心肌细胞(iPS-CM)忠实地概括了致心律失常的病理，并且外显子序列揭示的迄今未知的候选基因解释了不同的表型外显率。本研究的目的是：1.在一个LQT2家系中寻找与不完全外显有关的候选修饰基因。2.阐明LQT2家族成员来源的人心肌细胞的电生理变异性。3.确定候选疾病修饰基因变异体的表型。我们将通过研究表现出不一致临床表型的密切相关的LQT2 Herg R752W携带者对(即父子和同胞对)来实现这些目标。我们相信，目前的建议将提供一个基本的，机械性的解释，通过这个解释，在一个大的LQT2家族中可能会出现基因-表型不一致。这对个性化临床治疗具有潜在的重要意义，并将为旨在调节心脏功能障碍的离子通道的个性化药物干预提供新的靶点。

DESCRIPTION (provided by applicant): Sudden cardiac death (SCD) is a catastrophic event that accounts for up to 450,000 deaths each year in the US. Among patients at high risk for SCD are those with inherited cardiac arrhythmias. Long QT syndrome (LQTS) is one example of a group of inherited cardiac arrhythmias that produces defects in cardiac membrane currents. As a direct consequence, LQTS has been associated with prolongation of the QT interval on the ECG, ventricular arrhythmias, and an increased incidence of SCD. In LQTS2 well over two hundred missense mutations have been identified in the KCNH2 gene encoding hERG with the overwhelming majority thought to be characterized by protein processing and trafficking defects leading to a drastic reduction in potassium currents. However, as commonly observed in many autosomal dominant cardiac channelopathies the pattern of inheritance and clinical phenotypes of these patients are complex and often display incomplete penetrance, where disease-causing mutation carriers are asymptomatic. The causes for this variable clinical expressivity are not well understood but in the present research proposal, we will investigate this question by testing the hypothesis that modifier genes contribute to the variable clinical expressivity. Our multidisciplinary group at MetroHealth and Case Western Reserve University has studied clinically as well as in vitro a large 'Cleveland' LQT2 family carrying the hERG mutation R752W. Out of the 101 family members studied, 26 individuals carried the hERG R752W mutation. However, symptomatic LQTS was present in only 5 of the genetically affected family members thus illustrating incomplete penetrance of the disease. We hypothesize that the presence of disease modifying genes can explain the genotype-phenotype discordance observed in this LQT2 family. In this proposal, we will elucidate the mechanisms of incomplete penetrance in this LQT2 family using exome sequencing and cardiomyocytes differentiated from patient derived induced pluripotent stem cells (iPS). We hypothesize that patient-derived iPS differentiated cardiomyocytes (iPS-CM) faithfully recapitulate the arrythmogenic pathology and that heretofore unknown candidate genes revealed by exome sequencing account for variable phenotypic penetrance. The aims of this proposal are: 1. Identify candidate modifier genes responsible for incomplete penetrance in a LQT2 family. 2. Elucidate electrophysiological variability of human cardiomyocytes derived from LQT2 family members. 3. Determine the phenotype of candidate disease modifying gene variants. We will perform these aims by studying closely related LQT2 hERG R752W carrier pairs (i.e. father/son and sib pair) that display discordant clinical phenotype. We believe that the current proposal will offer a fundamental, mechanistic explanation by which genotype-phenotype discordance can arise in a large LQT2 family. This holds potentially significant ramifications for personalized clinical management and will offer novel targets for personalized pharmacologic intervention aimed at the modulation of dysfunctional ion channels in the heart.