The contribution of common and rare variants to autoimmunity in African Americans

描述(申请人提供)：多发性硬化症(MS)是一种常见而严重的中枢神经系统疾病，以髓鞘丢失、慢性炎症、轴突和少突胶质细胞病理以及进行性神经功能障碍为特征。虽然MS的确切原因尚不清楚，但在其发病机制中存在明确的、尽管是部分的遗传因素。尽管进行了长期密集的努力，但对多发性硬化症遗传学的了解仍然不完整。我们的总体目标是通过对非裔美国人的遗传学研究来帮助理解MS的发病机制。这一人群独特的遗传结构，以及非裔美国人和欧洲人之间多发性硬化症风险(和表型)的差异，为获得对疾病易感性和病因学的宝贵见解提供了独特的机会。这一建议建立在大量最近获得的数据的基础上，这些数据导致了一种假设，即罕见的基因组变异有助于疾病风险。它包括三个主要的研究目标，将基因组筛选与功能研究联系起来：在特定目标1中，我们将为具有代表性的非裔美国人多发性硬化症和对照基因组中具有强烈相关性的基因产生和分析高覆盖率的序列信息(调节区、外显子和外显子侧翼区)。从这个数据集中，大约500个变异将在验证队列中进行基因分型，以全面描述等位基因的异质性并发现特定于群体的相关稀有变异。在具体目标2中，我们建议以40倍的分辨率对一个多世代、多病例家族的基因组进行测序，并搜索按血统相同的DNA片段(IBD)，目的是识别与这个特定家族中疾病表达相关的罕见等位变异。此外，我们将使用高覆盖率的RNAseq来综合分析患病和未患病家庭成员的CD4+、CD8+和B细胞的MS转录组。最后，EVI5(ch.1p22.1)是一个经过充分验证的易感基因，在非裔美国人中显示出与MHC以外的最强关联。在具体目标3中，我们的目标是确定EVI5的等位基因差异如何有助于免疫突触的改变形成，从而促进MS的易感性。这里描述的大量和特征良好的样本集的可用性，再加上强大的实验室技术的帮助，为识别和表征MS相关基因提供了一个绝佳的机会。这些信息可能转化为临床有用的遗传生物标记物，并揭示治疗的新靶点。 公共卫生相关性：多发性硬化症(MS)是由中枢神经系统有髓神经束中断引起的严重神经功能障碍的常见原因。MS是仅次于创伤的年轻人神经功能障碍的第二大原因，全球约有200万人受到影响，美国有40多万人受到影响。值得注意的是，多发性硬化症的发病率在上个世纪似乎有相当大的增加，而且这种增加可能主要发生在女性身上。这种长期疾病的社会经济后果令人震惊，因为75%-85%的患者最终失业，处于社会孤立的高风险中。保守估计表明，仅在美国，这种慢性病每年导致的医疗费用就超过2000亿美元。因此，多发性硬化症是仅次于阿尔茨海默病的第二昂贵的神经疾病。尽管在治疗方面取得了重要进展，但目前可用的疾病修改药物中没有一种能令人信服地改变疾病的长期预后。临床表现非常多样，但对这种变异的潜在原因知之甚少。它可能是一种良性疾病，也可能是一种迅速演变和丧失能力的疾病。发病可能是突然或隐匿的，早期症状可能很严重，或者看起来很轻微，以至于患者可能几个月或几年都不去看医生。大多数患者最终会经历进行性残疾，在发病25年后，大约80%的受影响个人将需要帮助进行行走。因此，从长期来看，多发性硬化症通常是一种严重的疾病，需要对患者及其家人进行深刻的生活方式调整。我们的目标是识别编码与多发性硬化症易感性有关的产物的基因和基因特异性变体。为了实现我们的目标，我们将采集血液样本，从高、中、低MS风险人群中招募大量个体提取DNA。通过分析他们的遗传组成，我们将能够了解MS的遗传性规律。我们预计可能有几个基因参与了多发性硬化症的风险。这些基因可能独立发挥作用，也可能共同作用，并与环境因素共同影响易感性。遗传基因变异的特定组合也可能决定症状何时发展，或疾病如何进展。他们的识别将有助于确定MS的基本病因，改进风险评估，并影响治疗。

DESCRIPTION (provided by applicant): Multiple sclerosis (MS) is a common and severe CNS disorder that is characterized by myelin loss, chronic inflammation, axonal and oligodendrocyte pathology, and progressive neurological dysfunction. While the exact cause of MS is unknown, there is an unequivocal, albeit partial, genetic contribution to its pathogenesis. In spite of intensive long-standing efforts, the knowledge of MS genetics remains incomplete. Our overall goal is to contribute to the understanding of MS pathogenesis by means of genetic research in African Americans. The distinct genetic architecture of this population, together with the differences in MS risk (and phenotypes) between African Americans and Europeans, provide a unique opportunity to gain valuable insights into disease susceptibility and etiology. This proposal builds on a large body of recently acquired data leading to the hypothesis that rare genomic variants contribute to disease risk. It includes three main research goals that bridge genomic screens with functional research: In Specific Aim 1 we will generate and analyze high-coverage sequence information (regulatory regions, exons, and exon-flanking regions) for genes with strong evidence of association in representative African American MS and control genomes. From this dataset, approximately 500 variants will be genotyped in a validation cohort for the full description of allelic heterogeneity and the discovery of population-specific associated rare variants. In Specific Aim 2 we propose to sequence the genome of a multi-generational, multi-case family at 40x resolution and search for DNA segments identical by descent (IBD) with the goal of identifying rare allelic variants linked to disease expression in this particular family. In addition, we will use high coverage RNAseq to comprehensive analyze the MS transcriptome of CD4+, CD8+ and B cells in affected and unaffected family members. Finally, EVI5 (ch.1p22.1) is a well-validated susceptibility gene, and showed the strongest association outside the MHC in African Americans. In Specific Aim 3 our goal is to determine how allelic differences in EVI5 contribute to altered formation of the immunological synapse, thus contributing to MS susceptibility. The availability of a large and well characterized sample-set as described here, coupled with the aid of high-powered laboratory technologies, provide an outstanding opportunity to identify and characterize MS-related genes. This information may translate into clinically useful genetic biomarkers and reveal novel targets for therapy. PUBLIC HEALTH RELEVANCE: Multiple sclerosis (MS) is a common cause of severe neurological disability resulting from the interruption of myelinated tracts in the central nervous system. MS is second only to trauma as a cause of neurologic disability in young adults, affecting approximately 2 million people worldwide and more than 400,000 individuals in the US. Remarkably, the incidence of MS seems to have increased considerably over the last century, and this increase may have occurred primarily in women. The socioeconomic consequences of this long-lasting disease are staggering as 75- 85% of patients are eventually unemployed and at high risk for social isolation. Conservative estimates indicate that this chronic illness results in healthcare costs exceeding $200 billion annually in the United States alone. Thus, MS is the second most costly neurological disorder after Alzheimer's disease. Despite important advances in therapeutics, none of the currently available disease-modifying drugs convincingly alter the long-term prognosis of the disease. Clinical manifestations are extremely diverse, but very little is known about the underlying cause of this variability. It can vary from a benign illness to a rapidly evolving and incapacitating disease. Onset may be abrupt or insidious, and early symptoms may be severe or seem so trivial that a patient may not seek medical attention for months or years. Most patients ultimately experience progressive disability and twenty-five years after onset approximately 80% of affected individuals will require assistance with ambulation. Thus over the long-term, MS is most often a severe disease requiring profound lifestyle adjustments to the affected and their families. We aim to identify the genes and the gene-specific variants that code for products involved in MS susceptibility. To achieve our goals, we will collect blood samples to extract DNA from a large number of individuals recruited from populations at high, intermediate and low MS risk. By analyzing their genetic makeup, we will be able to understand the rules of MS heritability. We anticipate that there may be several genes involved in MS risk. These genes may work independently or together, and affect susceptibility in concert with environmental factors. Particular combinations of inherited genetic variants may also determine when symptoms develop, or how the disease progresses. Their identification will help to define the basic etiology of MS, improve risk assessment, and influence therapeutics.