The Contribution of Common and Rare Variants to Autoimmunity in African Americans

Investigator: Jorge Oksenberg, PhD
Sponsor: NIH National Institute of Neurological Disorders and Stroke

Location(s): United States


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.

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.