Genetic risk variants in African Americans with multiple sclerosis
ABSTRACT OBJECTIVES: To assess the association of established multiple sclerosis (MS) risk variants in 3,254 African Americans (1,162 cases and 2,092 controls). METHODS: Human leukocyte antigen (HLA)-DRB1, HLA-DQB1, and HLA-A alleles were typed by molecular techniques. Single nucleotide polymorphism (SNP) genotyping was conducted for 76 MS-associated SNPs and 52 ancestry informative marker SNPs selected throughout the genome. Self-declared ancestry was refined by principal component analysis of the ancestry informative marker SNPs. An ancestry-adjusted multivariate model was applied to assess genetic associations. RESULTS: The following major histocompatibility complex risk alleles were replicated: HLA-DRB1*15:01 (odds ratio [OR] = 2.02 [95% confidence interval: 1.54-2.63], p = 2.50e-07), HLA-DRB1*03:01 (OR = 1.58 [1.29-1.94], p = 1.11e-05), as well as HLA-DRB1*04:05 (OR = 2.35 [1.26-4.37], p = 0.007) and the African-specific risk allele of HLA-DRB1*15:03 (OR = 1.26 [1.05-1.51], p = 0.012). The protective association of HLA-A*02:01 was confirmed (OR = 0.72 [0.55-0.93], p = 0.013). None of the HLA-DQB1 alleles were associated with MS. Using a significance threshold of p < 0.01, outside the major histocompatibility complex region, 8 MS SNPs were also found to be associated with MS in African Americans. CONCLUSION: MS genetic risk in African Americans only partially overlaps with that of Europeans and could explain the difference of MS prevalence between populations.
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ABSTRACT: A wealth of data confirms that genetic variation is an important determinant of multiple sclerosis (MS) risk. Population, family and molecular studies provide strong empirical support for a polygenic model of inheritance, driven primarily by allelic variants relatively common in the general population. The major histocompatibility complex (MHC) in chromosome 6p21.3 represents by far the strongest MS susceptibility locus genome-wide and was unambiguously identified in all studied populations. The primary signal arises from the HLA-DRB1 gene in the Class II segment of the locus, with hierarchical allelic and haplotypic effects. Independent protective signals in the telomeric Class I region of the locus have been described as well. Over the last 6 years, large multicenter DNA collections have thrived and the development of new laboratory and analytical approaches has matured at a remarkable pace, allowing pursuit of comprehensive 'agnostic' genome-wide association studies to identify and characterise the non-MHC genetic component of MS. Taken together, the results have provided unambiguous evidence for the association of over 100 non-MHC loci with disease susceptibility. Follow-up experiments refined some of the association signals (IL2RA and CD58), identified gene-gene interactions (HLA-DRB1/EVI5) and revealed mechanistic insights into the functional consequences of the identified gene variants, most notably an increase in the soluble to membrane-bound ratio for IL-7, IL-2 and TNF receptors and a tyrosine-protein kinase 2-mediated immune deviation. These results significantly broaden our understanding of disease pathogenesis and permit, for the first time, modeling an individual's disease risk within the context of his or her familial history. Progress in identifying additional risk alleles is likely to be rapid in the near future. Although the effect of any given predisposing variant is modest, the possibility exists that multifaceted gene-gene and/or gene-environment interactions could substantially increase the contribution of some variants to the overall genetic risk. In addition, susceptibility genes may be subject to epigenetic modifications, which greatly increase the complexity of MS inheritance. Despite these remarkable advances, the knowledge of MS genetics remains incomplete. For example, a key but unresolved question is whether genetic variants influence disease trajectory. Ongoing efforts to fully characterize the repertoire of genes that predispose to MS and modulate its presentation is discussed. Functional characterization of even a moderate genetic effect on MS pathogenesis by a known gene or group of genes can assist in elucidating fundamental mechanisms of disease expression and yield important therapeutic opportunities.Expert Review of Neurotherapeutics 12/2013; 13(12 Suppl):11-9. DOI:10.1586/14737175.2013.865867 · 2.83 Impact Factor
- 12/2013; 4(s1). DOI:10.1111/cen3.12054
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ABSTRACT: Multiple sclerosis (MS) pathogenesis results from both genetic and environmental factors. Genome-wide association studies (GWAS) have contributed considerably to our understanding of MS susceptibility through identification of genetic variants influencing risk and quantitation of their effect sizes. Immunologically relevant genes, including genes in the major histocompatibility complex region, are the primary genetic contributors to MS susceptibility. MS prevalence differs according to population, and most GWAS carried out to date have used datasets from people of European descent. Interpretation and application of GWAS results from Europeans to other populations require a good understanding of the genetic characteristics of each population, such as linkage disequilibrium patterns. The heterogeneity in global MS prevalence is partially explained by differences in risk allele frequencies in populations, which are due to the effects of migration, adaptation to new environments and genetic heterogeneity. Genetic studies of different populations can be expected to narrow down the putative causative regions and improve our understanding of MS pathogenesis. The literature record of genetic studies of neuromyelitis optica is much shorter than that of MS. Genes associated with neuromyelitis optica have been reported in the major histocompatibility complex region, as well as at other genetic loci, but only the susceptibility associated with the HLA-DPB1*05:01 and HLA-DRB1*03 alleles, and the association of a CYP7A single nucleotide polymorphism have been replicated. Here, we describe important genetic studies of MS and neuromyelitis optica in Europeans, African Americans, and Asians, and discuss the implications for disease incidence and future directions for genetic research.02/2014; DOI:10.1111/cen3.12078