Multiple sclerosis (MS) is a common and severe disorder of the central nervous system characterized by chronic inflammation, myelin loss, gliosis, varying degrees of axonal and oligodendrocyte pathology, and progressive neurological dysfunction. MS pathogenesis includes a complex genetic component. In spite of intensive long-standing efforts by many research groups, the knowledge of MS genetics remains incomplete. Our overall objective is to characterize the repertoire of genes that predispose to MS and modulate its presentation. Their identification is now possible as a result of rapid progress in defining the landscape of genetic organization and cataloging variation across the human genome. We are using rigorous clinical criteria to ascertain 2000 MS patients and matched controls of African-American descent. The African American U.S. population is considered at moderate risk when compared to white Americans, perhaps reflecting the fact that MS is virtually absent in native African populations. Based on the hypothesis that genetic heterogeneity is inherent to MS, and the understanding that patterns of genomic disequilibrium are shaped by the history of each population, we propose a comprehensive genetic study of African Americans with MS to identify recombination events and minimal genomic regions harboring disease genes. Specific Aim 1 will test the hypothesis that there is an HLA-class I effect on susceptibility independent from class II genes, and test for evidence of association with combinations of HLA and KIR alleles. Specific Aim 2 describes a large high-resolution genome-wide association screen, together with a multi-analytical approach to map unambiguous association signals from sequence and copy number polymorphisms, leading to testable hypotheses as to which are the specific allelic variants conferring susceptibility. Specific Aim 3 takes advantage of the unique clinical features of African American MS patients and proposes a detailed analysis of phenotypic variables and their relationship to gene variants. This aim directly addresses the question of clinical heterogeneity in MS and the correlation between different phenotypes and genotypes. The availability of a unique, large, and well-characterized dataset provides an unprecedented opportunity to map MS-related genes. In addition, the generated whole- genome data in African American controls linked to precise assessment of admixture will serve as an important resource for the scientific community. Multiple sclerosis (MS), the prototypic demyelinating disease in humans, is a common cause of neurological dysfunction arising from early to middle adulthood. No curative therapy is currently available and approximately 90% of afflicted individuals are ultimately disabled. 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. We aim to map genes that code for products involved in MS pathogenesis. We anticipate that there may be several genes involved in MS. These genes may work independently or together and affect susceptibility in concert with environmental factors. Particular combinations of inherited genetic variations 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.