Congenital Myasthenic Syndromes: Pathogenic Mechanisms

描述(申请人提供)：先天性肌无力综合征(CMS)是一组不同类型的先天疾病，其特征是神经肌肉接头(NMJ)处的电脉冲传递障碍，由与NMJ功能有关的多个基因中的一个基因缺陷引起。在上个世纪，编码成人乙酰胆碱受体(AChR)亚单位基因(CHRNA1、CHRNB1、CHRND、CHRNE)和乙酰胆碱酯酶(AChE)胶原性尾巴(COLQ)的基因缺陷被证明是多种形式的CMS的原因。在过去的十年中，编码其他六个分子靶点的基因，包括胆碱乙酰转移酶(ChAT)、Rapsyn(RAPSN)、电压门控肌肉钠通道(SCN4A)、肌肉特异性激酶(Musk)、Dok-7(DOK7)和AChR的胎儿亚单位(CHRNG)，已被证明与其他类型的CMS的发病有关。我们最近报道了导致CMS的另一个突变靶点，即编码层粘连蛋白β2(LAMB2)的基因，使与CMS相关的基因总数达到12个。其他几个缺陷基因可能与CMS的发病机制有关，因为在大量CMS患者中，在上述基因中没有发现异常。这项拟议的研究是由这样一种假设驱动的，即NMJ的任何必要蛋白质的先天缺陷，如果没有有效的替代分子可用，就可能导致CMS。然而，对于检测引起CMS的遗传缺陷和防止这些疾病的复发来说，一个特别具有挑战性的问题是，事实上有非常大量的可能的候选基因，而在CMS表型中可以帮助寻找致病突变的线索很少。为了应对这一挑战，该项目的第一个具体目标是利用临床数据利用传统和新方法识别各种类型的CMS及其潜在的遗传缺陷；一种特殊类型的肌肉活组织检查，包括细胞内微电极研究；NMJ的电子显微镜和免疫组织化学；以及传统和新的DNA分析技术。该项目的第二个具体目标是在哺乳动物细胞系中进行表达研究，以表征已发现的突变的影响。该项目的长期目标是更好地了解CMS的发病机制，这可能导致这些神经肌肉疾病的有效治疗形式。

DESCRIPTION (provided by applicant): Congenital Myasthenic Syndromes (CMS), which are a heterogeneous group of inborn diseases characterized by impaired transmission of electrical impulses at the neuromuscular junction (NMJ), result from defects in one of multiple genes involved with the function of the NMJ. During the last century, defects in genes encoding the adult acetylcholine receptor (AChR) subunit genes (CHRNA1, CHRNB1, CHRND, CHRNE), and the acetylcholinesterase (AChE) collagenic tail (COLQ) were shown to cause several forms of CMS. During the last decade the genes encoding six other molecular targets, including the enzyme choline acetyltransferase (CHAT), rapsyn (RAPSN), the voltage-gated muscle sodium channel (SCN4A), the muscle-specific kinase (MUSK), Dok-7 (DOK7) and the fetal subunit of the AChR (CHRNG), have been demonstrated to be implicated in the pathogenesis of other types of CMS. We recently reported an additional target for mutations causing CMS, which is the gene encoding laminin beta 2 (LAMB2), bringing up the number of genes associated with CMS, to a total of twelve. Several other defective genes are likely to be involved in the pathogenesis of CMS since in a large number of patients affected with CMS no abnormalities can be found in the genes listed above. The proposed research is driven by the hypothesis that an inborn defect of any essential protein of the NMJ, for which no effective substituting molecule is available, can result in a CMS. However, a particularly challenging problem for detecting genetic defects causing CMS and preventing the reoccurrence of these diseases is the fact that there is a very large number of possible candidate genes and only very few clues in the CMS phenotype that can assist with the search for the causative mutation. In response to this challenge, the first specific aim of this project is to utilize conventional and novel methods of identification of the various types of CMS and their underlying genetic defects using clinical data; a special type of muscle biopsy, which includes intracellular microelectrode studies; electron microscopy of the NMJ and immunohistochemistry; as well as conventional and novel techniques for DNA analysis. The second specific aim of the project is to conduct expression studies in mammalian cell lines to characterize the effects of the discovered mutations. The long term goal of the project is to gain a better understating of the pathogenesis of CMS which may lead to effective forms of treatment for these neuromuscular disorders.