Discovery of modifier genes in cardiomyopathy

摘要 心肌病是一组遗传异质性心肌疾病， 治疗，最终导致心力衰竭（HF），移植或心脏性猝死（SCD）在许多患者。 尽管进行了数十年的深入研究，但仍然难以预测CM表型并解释临床异质性， 严重程度和预后。基因型-表型关联性差的可能原因是单个基因型中的突变 基因并不完全决定疾病的进程;相反，多个基因的相互作用，因果和修饰，可能 需要解释CM表型。我们筛选了患有各种类型CM的成人和儿童患者， 包括扩张型（DCM）、肥厚型（HCM）和限制型（RCM），使用全外显子组测序（641例患者） 和直接桑格测序（900例患者），并确定了myopalladin（MYPN），编码细胞骨架Z盘 蛋白质，作为一种与异质性CM表型相关的强致病基因，临床表现范围 从无症状的左心室肥大到扩张伴进行性HF到SCD或移植。所述CM 症状在个体患者之间差异很大，即使在携带的同一家庭成员中也是如此。 相同的突变。这些变异受到修饰基因的影响，修饰基因改变了主要致病基因的作用， 基因座然而，MYPN的修饰基因在很大程度上仍未被确定，并且可能依赖于以下因素的相互作用： MYPN相关基因通路和基因网络中的多个基因。修饰基因的鉴定现在是 从诊断、治疗和遗传咨询的角度来看，这是CM研究的一个重要目标，但它仍然是 在临床队列中非常具有挑战性。本研究的目的是确定修饰基因， 分子网络，使用组合的反向和 正向遗传学和系统遗传学分析。系统遗传学就是这样一种理解复杂 通过关注基因如何在群体中而不是单独地共同工作来预防疾病。我们已经证实了 与人类异质性表型相关的MYPN Q529 X导致基因敲入小鼠中的CM。我们有 开发了最大和最具特征的小鼠遗传参考群体（GRP），由150多个 C57 BL/6 J（B6）与DBA/2 J（D2）杂交获得的品系。D2菌株已被鉴定 作为小鼠CM模型，来自D2小鼠的CM表型在BXD品系家族中分离， 使BXD系列成为识别CM改性剂的优秀平台。此外，我们还推出了Q526 X-Mypn 突变（与人Q529 X-MYPN同源）到BXD遗传背景中，以检查不同的遗传背景如何影响基因表达。 背景改变了Mypn突变对CM表型的影响。这一建议是第一个 多学科协作努力鉴定人和小鼠中MYPN诱导的CM中的修饰基因。 使用跨物种验证源和强大的系统遗传学，我们将定义和验证新的修饰符 与Mypn相互作用并负责CM变异的基因。

Abstract Cardiomyopathies (CMs) are group of inherited heterogeneous diseases of heart muscle with no definite effective treatment, ultimately resulting in heart failure (HF), transplant or sudden cardiac death (SCD) in many patients. Despite decades of intense research, it is still difficult to predict CM phenotypes and explain clinical heterogeneity, severity and prognosis. The likely reason for poor genotype-phenotype association is that mutations in single gene do not completely determine disease course; rather interactions of multiple genes, causal and modifier, may be required to explain CM phenotypes. We have screened adult and pediatric patients with various types of CMs, including dilated (DCM), hypertrophic (HCM) and restrictive (RCM) using whole exome sequencing (641 patients) and direct Sanger sequencing (900 patients), and identified myopalladin (MYPN), encoding a cytoskeletal Z-disk protein, as a strong causal gene associated with heterogeneous CM phenotypes with clinical expressions ranging from asymptomatic left ventricular hypertrophy to dilation with progressive HF to SCD or transplant. The CM symptoms are highly varied among individual patients, even within the same family members who carry identical mutations. These variations are influenced by modifier genes that alter the effect of causal gene at major locus. However, modifier genes of MYPN remain largely unidentified and are likely to depend on the interaction of multiple genes in MYPN related gene pathways and gene networks. The identification of modifier genes is now a crucial goal of research in CMs from the viewpoints of diagnosis, treatment and genetic counseling, but it remains very challenging in clinical cohorts. The objective of the current study is to determine modifier genes and molecular networks that modulate severity of MYPN induced CMs using powers of combined reverse and forward genetics and systems genetic analysis. Systems genetics is such an approach to understand complex diseases by focusing on how genes work together in groups rather than singly. We have confirmed that mutation Q529X of MYPN associated with heterogeneous phenotypes in humans causes CM in knock-in mice. We have developed the largest and best characterized mouse genetic reference population (GRP) composed of over 150 lines derived from crosses between C57BL/6J (B6) and DBA/2J (D2) parents. The D2 strain has been identified as mouse CM model, and CM phenotypes from D2 mouse is segregated among the BXD family of strains, which makes BXD family as an excellent platform to identify CM modifiers. Moreover, we have introduced Q526X-Mypn mutation (homologous to human Q529X-MYPN) into BXD genetic background to examine how different genetic background modifies the effect of Mypn mutation on CM phenotypes. This proposal is one of the first multidisciplinary collaborative efforts to identify modifier genes in MYPN induced CM in both human and mouse. Using cross-species validation sources and powerful systems genetics, we will define and validate novel modifier genes that interact with Mypn and are responsible for CM variations.