Association studies in multiple sclerosis

The genetics of clinical outcome in multiple sclerosis

Multiple sclerosis (MS) is a common inflammatory disease of the central nervous system (CNS), the clinical course of which varies considerably between patients. Genetic complexity and interactions with as yet unknown environmental factors have hindered researchers from fully elucidating the aetiology of the disease. In addition to influencing disease susceptibility, epidemiological evidence suggests that genetic factors may affect phenotypic expression of the disease. Genes that affect clinical outcome may be more effective therapeutic targets than those which determine susceptibility. We present in this review a comprehensive survey of the genes (both MHC- and non-MHC-related) that have been investigated for their role in disease outcome in MS. Recent studies implicating the role of the genotype and epistatic interactions in the MHC in determining outcome are highlighted.

HLA DR and DQ interaction in myelin oligodendrocyte glycoprotein-induced experimental autoimmune encephalomyelitis in HLA class II transgenic mice

Multiple sclerosis (MS) is shown to be associated with the HLA class II genes. The presence of strong linkage disequilibrium between HLA DR and DQ molecules in humans makes it difficult to identify the individual roles of HLA DR and HLA DQ molecule in MS pathogenesis. To address this problem, we used HLA class II transgenic mice and the experimental autoimmune encephalitis (EAE) model. Administration of recombinant MOG (rMOG) induced severe inflammation and demyelination in the central nervous system (CNS) of HLA DRB1*1502 mice (60%), whereas no disease was observed in HLA DQB1*0601(0%) and mild disease was observed in DQB1*0302 mice (13%). Lymphocyte proliferation was blocked by anti HLA antibodies, confirming that the rMOG was functionally presented by the HLA molecules. Introduction of DQB1*0302 into DRB1*1502 mice resulted in the development of chronic progressive clinical disease characterized by severe inflammation and demyelination (90%) in response to immunization with rMOG, whereas mild disease was observed when DQB1*0601 was introduced in DRB1*1502 mice (30%). This would suggest that the presence of more than one susceptible allele, namely HLA DRB1*1502 and DQB1*0302 resulted in enhanced severity of disease in the DRB1*1502/DQB1*0302 mice, possibly due to the additional selection and expansion of potential autoreactive T cells. The use of defined single and double HLA transgenic mice may reveal the intricate interactions between class II molecules in human disease.

Treatment of multiple sclerosis: beyond the NICE guidelines

Multiple sclerosis (MS) is a common, disabling neurological condition whose pathogenesis is not clearly understood. Although current treatment recommendations assume an immunopathogenic disease mechanism, MS may not be an autoimmune disorder. Long-term immunological therapy for MS is in our view an untested approach, guided by uncritical acceptance of data from drug trials. We do not believe that there is convincing evidence that any of these immune-based treatments prevents long-term disease progression, or has much effect on common disabilities such as fatigue, pain, depression and cognitive impairment. The recent recommendations of the National Institute of Clinical Excellence did not address important issues regarding disease modification, management of paroxysmal symptoms and the likely therapeutic candidates for future treatment trials. We discuss treatment options for MS beyond the NICE guidelines.

Why we should offer routine vitamin D supplementation in pregnancy and childhood to prevent multiple sclerosis

Multiple sclerosis (MS) is a demyelinating disease of the central nervous system that runs a chronic course and disables young people. The disease is more prevalent in the geographic areas that are farthest from the equator. No form of treatment is known to be effective in preventing MS or its disabling complications. A number of epidemiological studies have shown a protective effect of exposure to sunlight during early life and a recent longitudinal study confirmed that vitamin D supplementation reduced life-time prevalence of MS in women. Very little is known regarding the role of vitamin D on the developing brain but experimental data suggest that cerebral white matter is vitamin D responsive and oligodendrocytes in the brain and spinal cord and express vitamin D receptors. It is possible that differentiation and axonal adhesion of oligodendrocytes are influenced by vitamin D level during brain development and a relative lack of vitamin D may increase oligodendroglial apoptosis. The age effect of migration on susceptibility to develop MS could be explained by a role of vitamin D on brain development. In areas of high MS prevalence, dietary supplementation of vitamin D in early life may reduce the incidence of MS. In addition, like folic acid, vitamin D supplementation should also be routinely recommended in pregnancy. Prevention of MS by modifying an important environmental factor (sunlight exposure and vitamin D level) offers a practical and cost-effective way to reduce the burden of the disease in the future generations.

TCR β polymorphisms and multiple sclerosis

A total of 267 families with two or more siblings with multiple sclerosis (MS) were genotyped with 14 restriction fragment length polymorphisms at the TCR beta locus. A nonparametric linkage analysis of the data showed no evidence for linkage to this locus (mlod=0.11). No significant allelic or haplotype transmissions were observed in the total sample of 565 patients. After stratification for the presence of HLA DRB1*15, an association was observed between the BV25S1*1-BV26S1*1-BV2S1*1 haplotype and MS (P=0.00089). This was not significant upon correction for multiple comparisons. It was also not significant when the haplotype frequency in affected individuals was compared to a normal control sample (P=0.77). Furthermore, the associated haplotype was followed-up in an independent sample of 97 nuclear families with a single DRB1*15-positive child with MS. The BV25S1*1-BV26S1*1-BV2S1*1 haplotype did not show significant evidence for transmission distortion but the same trend was seen (P=0.21). There were no significant associations observed in the DRB1*15-negative patients and no detectable difference was seen in the DRB1*15-positive BV25S1*1-BV26S1*1-BV2S1*1 association when comparing different subgroups based on clinical course of MS. These results show no evidence for linkage and fail to establish an association between MS susceptibility and the TCR beta locus.

Cytokine profile in patients with multiple sclerosis following vitamin D supplementation

Multiple sclerosis (MS) patients were randomized, in a double blind design, and placed into either a vitamin D supplemented group or a placebo control group. As expected, serum 25-hydroxyvitamin D levels increased significantly following 6 month vitamin D supplementation (17+/-6 ng/ml at baseline to 28+/-8 ng/ml at 6 months). Vitamin D supplementation also significantly increased serum transforming growth factor (TGF)-beta 1 levels from 230+/-21 pg/ml at baseline to 295+/-40 pg/ml 6 months later. Placebo treatment had no effect on serum TGF-beta 1 levels. Tumor necrosis factor (TNF)-alpha, interferon (IFN)-gamma, and interleukin (IL)-13 were not different following vitamin D supplementation. IL-2 mRNA levels decreased following vitamin D supplementation but the differences did not reach significance. Vitamin D supplementation of MS patients for 6 months was associated with increased vitamin D status and serum TGF-beta 1.

Bridging genetics and genomics in neurology

The Human Genome Project has stimulated a change in the ways human diseases are studied genetically. The field is moving towards a genome-wide approach to identifying susceptibility genes and to understanding the molecular basis of diseases. In this article, we review the emerging technologies and discuss results from studies that have used genomic approaches.

Multiple sclerosis: genomic rewards

A large body of immunologic, epidemiologic, and genetic data indicate that tissue injury in multiple sclerosis (MS) results from an abnormal immune response to one or more myelin antigens that develops in genetically susceptible individuals after exposure to an as-yet undefined causal agent. The genetic component of MS etiology is believed to result from the action of several genes of moderate effect. The incomplete penetrance of MS susceptibility alleles probably reflects interactions with other genes, post transcriptional regulatory mechanisms, and significant nutritional and environmental influences. Equally significant, it is also likely that genetic heterogeneity exists, meaning that specific genes influence susceptibility and pathogenesis in some affects but not in others. Results in multiplex MS families confirm the genetic importance of the MHC region in conferring susceptibility of MS. Susceptibility may be mediated by the class II genes themselves (DR, DQ or both), related to the known function of these molecules in the normal immune response, e.g. antigen binding and presentation and T cell repertoire determination. The possibility that other genes in the MHC or the telomeric region of the MHC are responsible for the observed genetic effect cannot be excluded. The data also indicate that although the MHC region plays a significant role in MS susceptibility, much of the genetic effect in MS remains to be explained. Some loci may be involved in the initial pathogenic events, while others could influence the development and progression of the disease. The past few years have seen real progress in the development of laboratory and analytical approaches to study non-Mendelian complex genetic disorders and in defining the pathological basis of demyelination, setting the stage for the final characterization of the genes involved in MS susceptibility and pathogenesis. Their identification and characterization is likely to define the basic etiology of the disease, improve risk assessment and influence therapeutics.

Complementation between specific HLA-DR and HLA-DQ genes in transgenic mice determines susceptibility to experimental autoimmune encephalomyelitis

To investigate the contribution of human leukocyte antigen (HLA) class II molecules in susceptibility to inflammatory demyelination, we induced experimental autoimmune encephalomyelitis (EAE) in transgenic (tg) mice expressing the HLA-DR3, HLA-DQ8 and HLA-DQ6 molecules in the absence of endogenous class II (Ab(o)). Following immunization with mouse myelin, HLA-DR3 tg mice mounted strong T-cell proliferative responses, and developed inflammatory lesions and demyelination in the central nervous system with mild to moderate clinical symptoms of EAE. HLA-DQ8 and HLA-DQ6 tg mice elicited weak T-cell proliferative responses and did not develop clinical symptoms of EAE. HLA-DR3/DQ6 double tg mice immunized with mouse myelin experienced clinical disease similar to the single tg HLA-DR3 tg mice, indicating that expression of DQ6 in this line had no effect on disease. In contrast, HLA-DR3/DQ8 double tg mice developed severe inflammatory lesions and clinical disease in response to immunization with mouse myelin. Our data suggest that in the presence of two susceptible class II alleles, namely HLA-DR3 and DQ8, there is additional selection and expansion of potential autoreactive T cells, resulting in enhanced severity of disease.

Expression of the human histocompatibility leukocyte antigen DR3 transgene reduces the severity of demyelination in a murine model of multiple sclerosis

The role of various MHC genes in determining the progression of multiple sclerosis (MS) remains controversial. The HLA-DR3 gene has been associated with benign relapsing MS in some genetic epidemiologic studies, but with disease progression in others. We induced demyelination in highly susceptible B10.M and B10.Q mice expressing the DR3 (HLA-DRB1*0301) transgene to determine directly the effects of a human transgene by infecting them with Theiler's murine encephalomyelitis virus (TMEV). DR3+ mice experienced a dramatic reduction in the extent and severity of demyelination compared with DR3- littermate controls, whereas anti-TMEV antibody titers, delayed-type hypersensitivity responses, and levels of infectious virus, virus antigen, and virus RNA were similar in both groups. To address a possible mechanism of how the human transgene is reducing virus-induced demyelination, we analyzed cytokine expression in the lesions and also determined whether B10.M mice can respond to peptides derived from the DR3 molecule. Intense staining for IFN-gamma and IL-4, T helper (TH) 1 and TH2 cytokines, respectively, was found in the lesions of TMEV-infected DR3- mice but not in the DR3+ transgenic mice at day 21 after infection. DR3 peptides elicited strong proliferative responses in B10.M mice but not in B10.M (DR3+) mice. These experiments are the first to demonstrate that a human class II DR gene can alter the severity of demyelination in an animal model of MS without influencing viral load. These experiments are consistent with a mechanism by which DR3 reduces demyelination by altering the cytokine expression in the lesions, possibly by deleting T cells involved in virus-induced pathology.

Susceptibility to relapsing-progressive multiple sclerosis is associated with inheritance of genes linked to the variable region of the TcR beta locus: use of affected family-based controls

We tested the hypothesis that susceptibility to relapsing-progressive (RP) (but not to relapsing-remitting [RR]) multiple sclerosis (MS) is associated with a gene linked to the TcR beta-chain variable region delimited by the Vbeta8-BamHI and Vbeta11-BamHI RFLP alleles in DRw15+ MS patients, using a contingency-table test of patient data and affected family-based controls. Control alleles and haplotypes were composed of parental marker alleles and haplotypes not transmitted to the affected child, in 90 simplex and 31 multiplex families from British Columbia. A total of 6,164 alleles at 11 loci were segregated through families of probands with RP MS or RR MS. The Vbeta8-Vbeta11 subhaplotype frequencies in the DRw15+ RP MS (but not RR MS) patients differed from control frequencies, because of an increase of the 2-1 subhaplotype (P=.02). Vbeta8-BamHI and Vbeta11-BamHI allele frequencies (P=.05 and .009, respectively) in the DRw15+ RP MS (but not RR MS) patients differed from control frequencies. The Vbeta1-Vbeta8 subhaplotype frequencies in the DRw15- RP MS (but not RR MS) patients differed from control frequencies (P=.03), with a significantly increased frequency of the 1-1 subhaplotype (P=.01; RR=7.1) in RP MS versus RR MS patients. Susceptibility to RP MS is associated both with a recessive inheritance of a gene linked to the 3' (Vbeta11) end of the 2-1 subhaplotype defined by the Vbeta8-BamHI and Vbeta11-BamHI alleles in DRw15+ patients and with a gene, located on the 1-1 subhaplotype, defined by the Vbeta1-TaqI and Vbeta8-MspI alleles of the TcR beta-chain complex in DRw15- patients.

Update on management and genetics of multiple sclerosis

Although the exact etiology of multiple sclerosis (MS) remains uncertain, there is an increasing body of evidence to support the role of genetic factors in MS susceptibility in general and the familial aggregation of MS in particular. MS.management continues to be largely symptom-specific. MS relapses are now frequently treated with IV-methylprednisone. In recent years, MS treatment trials are being conducted throughout the world. Interferon beta-1b has been approved as the first ongoing therapy for relapsing/remitting MS, although some issues/concerns remain to be addressed. In summary, while much research is still needed, important progress is being made in unravelling the etiology of MS and in developing management protocols which are not symptom- or relapse-specific.

Evidence for genetic basis of multiple sclerosis. The Canadian Collaborative Study Group

BACKGROUND Increased familial risks in multiple sclerosis (MS) range from 300-fold for monozygotic twins to 20-40-fold for biological first-degree relatives, suggesting a genetic influence. Yet if one identical twin has MS the other usually will not. One way of sorting out the contributions of genes and environment is to study half-sibs. METHODS In a Canadian population-based sample of 16 000 MS cases seen at 14 regional MS clinics one half-sib (or more) was reported by 939 index cases. By interview we elicited information on family structure and an illness in half-sibs and any full brothers or sisters. FINDINGS The age-adjusted MS rate in the 1839 half-sibs of these index cases was 1.32 percent compared with 3.46 percent for the 1395 full sibs of the same cases (p<0.001; likelihood ratio test). There were no significant differences in risk for maternal versus paternal half-sibs (1.42 percent vs 1.19 percent) or for those raised together versus those raised apart from the index case (1.17 percent vs 1.47 percent). INTERPRETATION Besides demonstrating the power and the feasibility of using half-sib studies to throw light on the aetiology of complex disorders, our findings show that a shared environment does not account for familial risk in MS and that maternal effects (such as intrauterine and perinatal factors, breastfeeding, and genomic imprinting) have no demonstrable effect on familial risk. Halving the number of potentially contributory genes (by comparing full-sib and half-sib rates) lowers the risk of MS by a factor of 2.62, an observation consistent with a polygenic hypothesis.

Genetics of autoimmune disease

In the past year, the major advances in understanding the genetics of autoimmune disease in both man and mouse have been made as a result of using the positional cloning approach. Construction of congenic mouse strains, and, in humans, the exploitation of linkage disequilibrium between very closely linked markers and disease-predisposing loci, is enabling fine mapping of these loci.

A genetic basis for familial aggregation in multiple sclerosis. Canadian Collaborative Study Group

Genetic-environmental interactions probably underlie spontaneous human autoimmune disorders, a category of complex traits thought to include multiple sclerosis (MS). The geographical distribution and familial aggregation of this disease have often been ascribed to the role of infectious agents, but there is no consensus. Increased family risks range from 300-fold for monozygotic twins to 20-40-fold for biological first-degree relatives over the general population prevalence of 0.1% (ref. 6). We screened a population-based sample of 15,000 individuals with MS by using standardized, personally administered questionnaires to identify adopted index cases and/or those who had adopted relatives. The frequency of MS among first-degree non-biological relatives living with the index case was no greater than expected from Canadian population prevalence data and significantly less than for biological relatives. These findings indicate that familial aggregation of MS is genetically determined: no effect of shared environment was detectable.

Multiple sclerosis and the HLA-D region: linkage and association studies

Inheritance patterns of multiple sclerosis (MS) in multiplex families suggest a complex aetiology involving environmental and genetically determined components. The association between the HLA class II DR15, DQ6, Dw2 haplotype and MS has been well documented in patients with ancestral origins in Northern Europe. Conversely, linkage analysis of this region in multiplex families, derived from a population base, has generated negative results. Thus, given the Dw2 specificity association, evidence implicating this locus in disease susceptibility appears contradictory. We have collected and determined the HLA-DR and -DQ haplotypes of 115 sibling pairs with multiple sclerosis, and confirm a significant association with the Dw2-associated haplotype, both in index cases and their affected siblings compared with controls. However, using a sibling pair linkage analysis that restricts haplotype sharing probabilities to defined genetic models, we have not observed linkage of this region to susceptibility in MS. We discuss the basis for association and linkage and conclude that the DR15, DQ6, Dw2 haplotype does represent a susceptibility locus but its contribution to the pathogenesis is small; although it may interact epistatically with other susceptibility genes, this haplotype is not necessary for disease expression.

Reactivity of normal T-cell lines to MBP isolated from normal and multiple sclerosis white matter

T-cell reactivity to human myelin basic protein (MBP) has been extensively studied using T-cell lines and clones generated from both peripheral blood and cerebrospinal fluid, from normal controls and multiple sclerosis (MS) patients. These studies have largely utilized myelin basic protein isolated from control human adult white matter. In our study, we used MBP reactive T-cell lines as a probe to investigate antigenic differences in a series of MBP preparations isolated from either control human white matter or white matter from the central nervous system (CNS) of MS patients. Autologous peripheral blood derived mononuclear cells were used as antigen presenting cells (APC). Although the majority of T-cells were found to react equally well with all preparations of MBP isolated from both control and MS white matter, we were also able to identify T-cell lines which reacted well with all preparations of MBP isolated from controls but failed to react with MBP isolated from MS white matter. These differences were unlikely to reflect differences in degradation products or excess peptides present in the MS brain since SDS-PAGE and HPLC did not show any difference in the MS samples compared to the controls, and the concentration response curves for a human T-cell clone specific for the 84-102 region of MBP were similar for all the MBP preparations. We did not detect differences in amino acid content amongst MBP preparations although single amino acid substitutions cannot be ruled out. These results raise the possibility that MBP isolated from MS brain may differ in charge microheterogeneity which would affect antigenic determinants.(ABSTRACT TRUNCATED AT 250 WORDS)