Rare and Novel Genetic Variation in the Pathogenesis of Cerebellar Ataxia

描述（由申请人提供）： 小脑的退化会导致共济失调，这是一种平衡和协调的障碍，可以严重致残，并使患者无法行走，说话或进行协调运动。遗传性共济失调影响着全世界50万人，但目前的测试只确定了大约50%的相关基因。更好的诊断将导致更好的治疗，发现新的疾病基因可以为小脑的工作提供新的见解，并提出对抗其退化的方法。新技术被称为下一代测序，是一种具有成本效益的方法，可以检查整个人类基因组或编码蛋白质的关键部分，称为外显子组，并可用于全面调查患者的新基因突变。加州大学洛杉矶分校共济失调和神经遗传学项目拥有独特的资源来研究这种遗传变异，拥有来自数百名患有小脑共济失调的个人和家庭的大量DNA样本，所有这些都具有精确详细的临床信息。 1)我们将检查20个具有显性（10）或隐性（10）遗传的共济失调家族的外显子组，所有这些家族都对最常见的已知遗传性共济失调呈阴性筛选。我们将首先确认先证者在罕见（<1%）共济失调基因中没有变异，然后继续鉴定新的致病变异。我们已经开发了一种排除良性多态性的管道，只分离那些导致神经系统疾病的可能性最高的变异。对于在此分析后仍未确定的患者和家庭，我们将检查其基因组中可能改变基因表达和/或调控的致病变异。我们将估计我们在共济失调患者人群中发现的基因突变的发生率，并确认它们在正常个体中没有发现。 2)尽管家庭检查对于识别新疾病基因至关重要，但在共济失调诊所就诊的大多数未确诊患者缺乏明确的疾病家族史。为了解决这些个体，我们将检查具有类似详细临床表现的患者亚组，因为他们最有可能共享共同的遗传原因。我们将首先将我们的分析管道应用于一个特定的明确定义的纯小脑共济失调亚型，以分离潜在的致病基因和突变。 3)最后，我们将使用人类神经元在细胞培养系统中筛选已识别的变体，并进行各种测试，旨在量化突变对基本细胞功能的严重性。该信息将用于表征和优先考虑具有未知临床意义的变体，以进行进一步详细分析。 总之，这项研究将提供一个 全面了解小脑性共济失调背后的遗传病因，定义对小脑正常功能重要的新分子途径，有助于临床诊断的进步，并有助于阐明引起退行性共济失调的机制。

DESCRIPTION (provided by applicant): Degeneration of the cerebellum causes ataxia, a disorder of balance and coordination which can be severely disabling and render afflicted individuals unable to walk, speak, or make coordinated movements. Genetic ataxia affects half a million people worldwide, but current testing only identifies roughly 50% of the responsible genes. Better diagnosis will lead to better treatment and uncovering novel disease genes could provide new insight into the workings of the cerebellum and suggest ways to combat its degeneration. New technology, termed next-generation sequencing, is a cost-effective means of examining either the entire human genome or the key portion that codes for protein, known as the exome, and can be used to comprehensively investigate patients for novel genetic mutations. The UCLA Ataxia and Neurogenetics Program possesses a unique resource for studying this genetic variation with a large bank of DNA samples from hundreds of individuals and families with cerebellar ataxia, all with precisely detailed clinical information. 1) We will examine the exomes of 20 ataxic families with dominant (10) or recessive (10) inheritance, all screened negative for the most common known genetic ataxias. We will initially confirm probands possess no variants in rare (<1% worldwide) ataxia genes and then proceed to identifying novel causative variants. We have developed a pipeline for excluding benign polymorphisms and isolating only those variants with the highest probability of causing neurologic disease. For patients and families remaining unidentified following this analysis, we will examine their genomes for disease-causing variants potentially altering gene expression and/or regulation. We will estimate the occurrence of mutations in genes we discover within our ataxia patient population and confirm that they are not found in normal individuals. 2) Although examination of families is essential to the identification of new disease genes, the majority of undiagnosed patients seen in ataxia clinics lack a clearly defined family history of disease. To address these individuals, we will examine subgroups of patients with similar detailed clinical presentations as they will be most likely to share common genetic causes. We will initially apply our analysis pipeline across a specific well- defined subtype of pure cerebellar ataxia to isolate potential disease-causing genes and mutations. 3) Lastly, we will screen identified variants in a cell culture system using human neurons with a variety of tests designed to quantitate the severity of the mutations on basic cellular functioning. This information will be used to characterize and prioritize variants of unknown clinical significance for further detailed analysis. In summary, this study will provide a comprehensive view of the genetic etiologies behind cerebellar ataxia, define new molecular pathways important to the normal function of the cerebellum, contribute to advancements in clinical diagnosis, and help elucidate the mechanisms causing degenerative ataxia.