Follow-up investigation of 12 proposed linkage regions in multiple sclerosis

Effect of Vitamin D on Experimental Autoimmune Neuroinflammation Is Dependent on Haplotypes Comprising Naturally Occurring Allelic Variants of CIITA (Mhc2ta)

An increasing body of evidence associates low vitamin D levels with increased risk of multiple sclerosis (MS), suggesting the possibility of a gene-environment interaction for this environmental factor in MS pathogenesis. Moreover, it has been shown that vitamin D downregulates major histocompatibility complex (MHC) class II expression in experimental autoimmune encephalomyelitis (EAE), an animal model of MS. We here report about the impact of a dietary vitamin D supplementation on EAE in the rat strains having functionally relevant allelic variations in the CIITA (Mhc2ta) gene, a master regulator of MHC class II expression. Full length myelin oligodendrocyte glycoprotein (MOG)-EAE was induced in DA.PVG^av1-Vra4 congenic rats harboring the Vra4 locus from PVG strain in the EAE- susceptible DA background, and compared to the parental strains. The congenic rats fed with either vitamin D supplemented, deprived or regular diet developed an intermediate clinical EAE phenotype, in contrast to DA and PVG strains. Immunopathological studies revealed vitamin D dose-dependent effect on demyelination and inflammatory infiltration of the central nervous system (CNS), expression of MHC class II and CIITA, as well as downregulation of a range of pro-inflammatory genes. Taken together, our findings demonstrate an impact of vitamin D on the target tissue pathology and peripheral immune response during EAE in DA.PVG^av1-Vra4 congenic strain. Thereby, our data provide evidence of a modulatory effect of vitamin D in context of genetic variances in the Vra4 locus/Mhc2ta gene in MS-like neuroinflammation, with potential relevance for the human demyelinating disease.

Multiple loci comprising immune-related genes regulate experimental neuroinflammation

A 58 Mb region on rat chromosome 4 known to regulate experimental autoimmune encephalomyelitis (EAE) was genetically dissected. High-resolution linkage analysis in an advanced intercross line (AIL) revealed four quantitative trait loci (QTLs), Eae24-Eae27. Both Eae24 and Eae25 regulated susceptibility and severity phenotypes, whereas Eae26 regulated severity and Eae27 regulated susceptibility. Analyses of the humoral immune response revealed that the levels of serum anti-myelin oligodendrocyte glycoprotein (MOG) immunoglobin G1 (IgG1) antibodies are linked to Eae24 and anti-MOG IgG2b antibodies are linked to both Eae24 and Eae26. We tested the parental DA strain and six recombinant congenic strains that include overlapping fragments of this region in MOG-EAE. Eae24 and Eae25 showed significant protection during the acute phase of EAE, whereas Eae25 and Eae26 significantly modified severity but not susceptibility. The smallest congenic fragment, which carries Eae25 alone, influenced both susceptibility and severity, and protected from the chronic phase of disease. These results support the multiple QTLs identified in the AIL. By demonstrating several QTLs comprising immune-related genes, which potentially interact, we provide a significant step toward elucidation of the polygenically regulated pathogenesis of MOG-EAE and possibly multiple sclerosis (MS), and opportunities for comparative genetics and testing in MS case-control cohorts.

Variants in ST8SIA1 do not play a major role in susceptibility to multiple sclerosis in Canadian families

Multiple sclerosis (MS) is a complex trait with a significant genetic component. Recent work has implicated the ST8SIA1 gene, encoding a ganglioside synthase, in susceptibility to the disease, perhaps with a parent-of-origin effect. In this investigation of 1318 MS patients from 756 Canadian families, we analysed the transmission of the four single nucleotide polymorphisms in ST8SIA previously shown to be associated with MS. No significant association was found in the entire sample or when stratifying by transmitting parent, indicating that this gene plays little or no role in susceptibility to MS in the Canadian population.

Association of smoking behavior with an odorant receptor allele telomeric to the human major histocompatibility complex

Smoking behavior has been associated in two independent European cohorts with the most common Caucasian human leukocyte antigen (HLA) haplotype (A1-B8-DR3). We aimed to test whether polymorphic members of the two odorant receptor (OR) clusters within the extended HLA complex might be responsible for the observed association, by genotyping a cohort of Hungarian women in which the mentioned association had been found. One hundred and eighty HLA haplotypes from Centre d'Etude du Polymorphisme Humain families were analyzed in silico to identify single-nucleotide polymorphisms (SNPs) within OR genes that are in linkage disequilibrium with the A1-B8-DR3 haplotype, as well as with two other haplotypes indirectly linked to smoking behavior. A nonsynonymous SNP within the OR12D3 gene (rs3749971(T)) was found to be linked to the A1-B8-DR3 haplotype. This polymorphism leads to a (97)Thr --> Ile exchange that affects a putative ligand binding region of the OR12D3 protein. Smoking was found to be associated in the Hungarian cohort with the rs3749971(T) allele (p = 1.05 x 10(-2)), with higher significance than with A1-B8-DR3 (p = 2.38 x 10(-2)). Our results link smoking to a distinct OR allele, and demonstrate that the rs3749971(T) polymorphism is associated with the HLA haplotype-dependent differential recognition of cigarette smoke components, at least among Caucasian women.

Linkage disequilibrium analyses within chromosome 19p in multiple sclerosis

OBJECTIVE

The aim of this study was to determine if multiple sclerosis (MS) shows association with variants of single nucleotide polymorphisms (SNP) within chromosome 19p, where previous studies resulted in conflicting observations. Subjects and methods The transmissions of 569 SNP variants and 608 haplotypes from unaffected parents to their affected children were tested in 257 Caucasian families by using the pedigree disequilibrium test (PDT), the TRANSMIT version 2.5 program and the family- and haplotype-based association tests (FBAT and HBAT). The distribution of linkage disequilibrium (LD) among SNPs in 19p was assessed by ldmax and correlated with the location of MS-associated haplotypes.

RESULTS

Individual SNP alleles did not show association after correction for multiple testing in PDT. Several marker haplotypes within potential candidate genes of intracellular enzymes, transmembrane proteins and receptors and signaling and adhesion molecules appeared to be weakly associated with the disease in both TRANSMIT and HBAT. However, none of the associations was strong enough to survive correction for multiple testing.

CONCLUSIONS

The present study is in the line of previous studies with negative conclusions concerning the role of the 19p region in MS.

Multiple sclerosis susceptibility and the X chromosome

Multiple sclerosis (MS) is a chronic autoimmune complex trait with strong evidence for a genetic component. A female gender bias is clear but unexplained and a maternal parent-of-origin effect has been described. X-linked transmission of susceptibility has been previously proposed, based on pedigree, association and linkage studies. We genotyped 726 relative pairs including 552 affected sib-pairs for 22 X-chromosome microsatellite markers and a novel dataset of 195 aunt-uncle/niece-nephew (AUNN) affected pairs for 18 markers. Parent-of-origin effects were explored by dividing AUNN families into likely maternal and paternal trait transmission. For the sib-pair dataset we were able to establish exclusion at a lambda s = 1.9 for all markers using an exclusion threshold of LOD < or = -2. Similarly for the AUNN dataset, we established exclusion at lambdaAV = 1.9. For the combined dataset we estimate exclusion of lambda = 1.6. We did not identify significant linkage in either the sib-pairs or the AUNN dataset nor when datasets were stratified for the presence/absence of the HLA-DRB1*15 allele or for paternal or maternal transmission. This comprehensive scrutiny of the X-chromosome suggests that it is unlikely to harbour an independent susceptibility locus or one which interacts with the HLA. Complex interactions including epigenetic ones, and masking by balanced polymorphisms are mechanisms not excluded by the approach taken.

Multiple sclerosis: the environment and causation

PURPOSE OF REVIEW

We review current thinking on the aetiology of multiple sclerosis, how genetic susceptibility interacts with environmental risk factors at the population level, multiple sclerosis-associated risk factors and contemporary causation theory.

RECENT FINDINGS

Two large genomic studies have confirmed the unambiguous associations with the DRB1 and DQB alleles of the human leucocyte antigen class II region. No other region with genome-wide significance has been identified. Family-based genetic epidemiological approaches have found no evidence of nongenetic transmissibility. This indicates that the action of the environment in influencing multiple sclerosis risk is operative at a macroenvironmental or population level, and not within families or the microenvironment. Environmental factors receiving renewed attention include vitamin D status, Epstein-Barr virus infection and smoking. Bradford Hill's criteria for causation have been modified and should be adopted as a framework for demonstrating causation in relationship to multiple sclerosis.

SUMMARY

Multiple sclerosis is a complex disease because of interaction between genes and the environment. Any theory of causation for a specific agent will have to be congruent with the biology of the disease.