Congenital Myasthenic Syndromes: Pathogenic Mechanisms

描述（由申请人提供）：先天性肌无力综合征（CMS）是一组异质性先天性疾病，其特征在于神经肌肉接头（NMJ）处电脉冲传递受损，由参与NMJ功能的多个基因之一的缺陷引起。在上个世纪，编码成人乙酰胆碱受体（AChR）亚基基因（CHRNA 1，CHRNB 1，CHRND，CHRNE）和乙酰胆碱酯酶（AChE）胶原尾（COLQ）的基因缺陷被证明会导致几种形式的CMS。在过去的十年中，编码其他六种分子靶点的基因，包括胆碱乙酰转移酶（CHAT），rapsyn（RAPSN），电压门控肌肉钠通道（SCN 4A），肌肉特异性激酶（MUSK），Dok-7（DOK 7）和AChR的胎儿亚基（CHRNG），已被证明与其他类型CMS的发病机制有关。我们最近报告了导致CMS的突变的另一个靶点，即编码层粘连蛋白β 2（LAMB 2）的基因，使与CMS相关的基因数量达到总共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，在上述基因中未发现异常。这项研究的假设是，NMJ的任何必需蛋白质的先天缺陷（没有有效的替代分子）都可能导致CMS。然而，检测引起CMS的遗传缺陷和预防这些疾病复发的特别具有挑战性的问题是，在CMS表型中存在非常大量的可能的候选基因，并且只有非常少的线索可以帮助寻找致病突变。为了应对这一挑战，该项目的第一个具体目标是利用传统和新的方法，利用临床数据识别各种类型的CMS及其潜在的遗传缺陷;一种特殊类型的肌肉活检，包括细胞内微电极研究; NMJ和免疫组织化学的电子显微镜;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，以表征所发现的突变的影响。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.