Further localization of a multiple sclerosis susceptibility gene on chromosome 7q using a new T cell receptor beta-chain DNA polymorphism

Reduced expression of human endogenous retrovirus (HERV)-W GAG protein in the cingulate gyrus and hippocampus in schizophrenia, bipolar disorder, and depression

The human endogenous retrovirus (HERV)-W multicopy family was identified in human DNA from the previously characterized multiple sclerosis associated retroviral element (MSRV). Upregulation of the HERV-W POL has been reported in cerebrospinal fluid of patients with schizophrenia. The expression of capsid (GAG) protein of HERV-W was studied by immunohistochemistry and western blotting in postmortem brain tissue of the anterior cingulate cortex and hippocampal formation of normal controls and of patients with schizophrenia, bipolar disorder and major depression. A physiological expression of GAG protein was detected in neurons as well as astroglial cells in normal brain both in the anterior cingulate cortex and in the hippocampal formation. There was a statistically significant reduction of this expression in neurons and astroglial cells in brains from individuals with schizophrenia, major depression, and bipolar disorder. The results from the present study confirm that GAG protein encoded by the HERV-W multicopy gene family is expressed in cells of the central nervous system under normal conditions. Our findings of a cell type-, brain region- and disease-specific reduced expression in schizophrenia, major depression, and bipolar disorder are compatible with a pathophysiological role of HERVs in human brain disorders. The causes and biological consequences of this differential regulation will be the subject of further investigations.

Human endogenous retrovirus (HERV)-W ENV and GAG proteins: Physiological expression in human brain and pathophysiological modulation in multiple sclerosis lesions

Antigen expression of a human endogenous retrovirus family, HERV-W, in normal human brain and multiple sclerosis lesions was studied by immunohistochemistry by three independent groups. The HERV-W multicopy family was identified in human DNA from the previously characterized multiple sclerosis-associated retroviral element (MSRV). A panel of antibodies against envelope (ENV) and capsid (GAG) antigens was tested. A physiological expression of GAG proteins in neuronal cells was observed in normal brain, whereas there was a striking accumulation of GAG antigen in axonal structures in demyelinated white matter from patients with MS. Prominent HERV-W GAG expression was also detected in endothelial cells of MS lesions from acute or actively demyelinating cases, a pattern not found in any control. A physiological expression of ENV proteins was detected in microglia in normal brain; however,a specific expression in macrophages was apparently restricted to early MS lesions. Thus, converging results from three groups confirm that GAG and ENV proteins encoded by the HERV-W multicopy gene family are expressed in cells of the central nervous system under normal conditions. Similar to HERV-W7q ENV (Syncitin), which is expressed in placenta and has been shown to have a physiological function in syncytio-trophoblast fusion, HERV-W GAG may thus also have a physiological function in human brain. This expression differs in MS lesions, which may either reflect differential regulation of inherited HERV-W copies, or expression of "infectious" MSRV copies. This is compatible with a pathophysiological role in MS, but also illustrates the ambivalence of such HERV antigens, which can be expressed in cell-specific patterns, under physiological or pathological conditions.

Expression of the human endogenous retrovirus HERV-W family in various human tissues and cancer cells

We examined the structural genes (gag, pol and env) of the human endogenous retrovirus (HERV-W) family from 12 normal human tissues and 18 human cancer cell lines using RT-PCR. For the gag and pol genes, their expression patterns showed tissue or cell specificity, depending on the samples, whereas the env gene was expressed in all tissues and cancer cells examined. To identify active HERV-W elements in tissues and cancer cells, the RT-PCR products were cloned and sequenced. Ninety-five clones for the env gene, 55 clones for the pol gene and 17 clones for the gag gene of the HERV-W family were isolated from human tissues and sequenced, while 85 clones for the env gene, 61 clones for the pol gene and no clones for the gag gene of the HERV-W family were isolated and sequenced from cancer cells. Among these clones, 50 clones from tissues and 44 from cancer cells showed putative amino acids of the HERV-W env gene, while only two clones from cancer cells showed putative amino acids of the HERV-W pol gene. Phylogenetic analysis indicated that several clones identified previously from human monochromosomes had sister relationships with the clones from the different tissues and cancer cells. These data suggest that HERV-W elements are actively expressed in human tissues and cancer cells. These active HERV-W elements deserve further investigation as potential causative agents of various human diseases including cancers.

T cell receptor beta chain genotyping in Australian relapsing-remitting multiple sclerosis patients

This study focused on susceptibility to MS within the beta-chain of the T-cell antigen receptor (TCRB locus, 7q35) in a cohort of 122 RR-MS patients compared with 96 normal individuals using biallelic polymorphisms across the bv8s1(Vbeta8.1) to bv11s1 (Vbeta11) TCRB subregion. The markers bv6s5, bv8s1, bv10s1, bv15s1 and bv3s1 were studied for allele and genotype frequencies; haplotypes were assigned with combinations of two of these markers and stratification for HLA-DR15 was also performed. Linkage disequilibrium was found between alleles of the bv8s1, bv10s1/bv15s1 and bv3s1 loci in both patients and controls. An increase among RR-MS patients in the allele frequency of bv8s1*2 (P=0.03) and the haplotype bv8s1*2/bv3s1*1 (P=0.006) was noted and both were found to be statistically significant. In the DR15-positive group, the association between TCRB and MS was seen with the bv8s1*2 allele (Puc=0.05) and the bv8s1*2/bv10s1 haplotypes (Puc=0.048), while the haplotype associations seen among DR15-negative RR-MS patients included the bv3s1*1 allele (bv10s1*1/ bv3s1*1, Puc=0.022; bv8s1*2/bv3s1*1, Puc=0.048). These results support the involvement of the TCRB region in MS susceptibility and encourage further study of the variable gene segments in this region.

Genome-Wide Linkage Analysis of Chronic Relapsing Experimental Autoimmune Encephalomyelitis in the Rat Identifies a Major Susceptibility Locus on Chromosome 9

The immunization of inbred Dark Agouti (DA) rats with an emulsion containing homogenized spinal cord and CFA induces chronic relapsing experimental autoimmune encephalomyelitis (EAE), a disease with many similarities to multiple sclerosis. We report here the first genome-wide search for quantitative trait loci regulating EAE in the rat using this model. We identified one quantitative trait locus on chromosome 9, Eae4, in a [DA(RT1av1) × BN(RT1n)]F2 intercross showing linkage to disease susceptibility and expression of mRNA for the proinflammatory cytokine IFN-γ in the spinal cord. Eae4 had a larger influence on disease incidence among rats that were homozygous for the RT1av1 MHC haplotype (RT1av1 rats) compared with RT1n/av1 rats, suggesting an interaction between Eae4 and the MHC. Homozygosity for the DA allele at markers in Eae4 and in the MHC was sufficient for EAE. Thus, Eae4 is a major genetic factor determining susceptibility to EAE in this cross of DA rats. In addition, there was support for linkage to phenotypes of EAE on chromosomes 1, 2, 5, 7, 8, 12, and 15. The chromosome 12 region has been shown previously to predispose DA rats to arthritis, and the chromosome 2 region is syntenic to Eae3 in mice. We conclude that Eae4 and probably the other identified genome regions harbor genes regulating susceptibility to neuroinflammatory disease. The identification and functional characterization of these genes may disclose critical events in the pathogenesis of multiple sclerosis; understanding these events could be essential for the development of new therapies against the disease.

Inheritance of susceptibility to multiple sclerosis

In recent years, epidemiological evidence supporting the genetic basis of multiple sclerosis has been extended and whole-genome linkage screening has advanced the mapping of the involved genes. Understanding of the known HLA associations has also improved and many candidate genes have been studied.

Quantitative trait loci disposing for both experimental arthritis and encephalomyelitis in the DA rat; impact on severity of myelin oligodendrocyte glycoprotein-induced experimental autoimmune encephalomyelitis and antibody isotype pattern

Quantitative trait loci (QTL) controlling inflammatory diseases with different organ specificity may hypothetically either be unique for one disease or shared among different diseases. We have investigated whether five non-MHC QTL controlling susceptibility to experimental arthritis in the DA rat also influence myelin oligodendrocyte glycoprotein (MOG)-induced experimental autoimmune encephalomyelitis (EAE) in an F2 intercross between inbred DA and PVG.RT1a rats. Two of the five chromosome regions affecting arthritis in the DA rat also regulate phenotypes of EAE. The DA allele at markers in Cia3 (collagen-induced arthritis QTL) on chromosome 4 is associated with more severe EAE and high levels of anti-MOG antibodies of the IgG2c subclass. Since production of antibodies of the IgG2c subclass may be stimulated by Th1 cells, and there is previous evidence that such cells promote EAE, it is possible that both of the studied phenotypes are controlled by the same gene or genes regulating Th1/Th2 cell differentiation. Furthermore, we show that Oia2 (oil-induced arthritis QTL) on chromosome 4 regulates levels of anti-MOG antibodies of the IgG1 subclass and of anti-MOG IgE, but that this gene region does not affect clinical disease severity in our study. Since production of IgE and IgG1 may be stimulated by Th2 cells, this QTL may also control Th1/Th2 bias. We conclude that Cia3 and Oia2 regulate MOG-induced EAE in rats. Furthermore, since both EAE and arthritis phenotypes co-localize to these gene regions, they may harbor genes which are key regulators of pathogenic immune responses.

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.

Identification of multiple sclerosis-associated genes

Multiple sclerosis (MS) is a complex genetic trait. Analyses to identify genetic variants that increase susceptibility to MS have primarily focused on candidate genes, either in family linkage investigations or in association (linkage disequilibrium) studies in sporadic cases and control subjects. Most of the candidate genes considered to date either influence immune function or encode structural myelin proteins. Recently, three preliminary whole genomic surveys were completed, and they reveal multiple loci of possible genetic linkage that are worthy of further study. No convincing evidence for a single strong locus has emerged from analysis of the three studies. Linkage promises to focus the future choice of candidate genes for further investigation.

Evolution and selection of primate T cell antigen receptor BV8 gene subfamily

The set of potential T cell receptor specificities is highly diverse. The relative contributions of T cell receptor (TCR) V beta gene segment polymorphisms, duplications, deletions, and gene conversions to this final T cell receptor protein diversity are unknown. To study these mechanisms, we sequenced and compared closely related primate TCR gene segments from BV8S1, S2, and S5. Interspecies comparisons show that these gene segments have sustained multiple duplication, gene conversion, and deletion events during the last 35 million years of anthropoid primate evolution. BV8 coding sequences are generally conserved with respect to their flanking noncoding sequences, but we find no evidence for positive or negative selection in sequences coding for the first two putative complementarity-determining (ligand-binding) regions. Sequences of TCRBV8 gene segments from unrelated humans demonstrate no nonsynonymous substitutions in nonleader regions of either the BV8S1 or S2 gene segments. We conclude that gene duplication, deletion, and conversion mechanism contribute in a substantial way to the overall diversity of the TCRBV8 gene segment repertoire in primate evolution and that germline substitutions and consequent polymorphisms in CDRs 1 and 2 of these gene segments probably do not play an active role in generating TCR beta chain protein variation.

The genetic analysis of multiple sclerosis

Although monogenic diseases often show extreme clinical phenotypes, the major burden of genetic ill health lies in the more prevalent polygenic disorders, such as diabetes, hypertension and multiple sclerosis. These conditions affect many thousands of individuals and their management consumes vast amounts of health care resources: in the UK some 80,000 people have multiple sclerosis; the estimated financial cost to society of introducing treatments, such as beta interferon, could be as high as 250 million pounds per year. Knowledge on the genetics of these common diseases is poor, but has potentially received a considerable boost with the arrival of whole genome screening. The genome screen in insulin-dependent diabetes mellitus (IDDM) reported in 1994 was the first in a human polygenic disease. Since this publication, whole genome screening has been performed in a variety of human polygenic diseases, including schizophrenia, bipolar affective disorder, non-insulin-dependent diabetes mellitus (NIDDM), inflammatory bowel disease, asthma and multiple sclerosis.

Genetic predisposition to multiple sclerosis as revealed by immunoprinting

This study was designed to examine the immunogenetic background predisposing to multiple sclerosis (MS). Three hundred fifty-eight clinically well-characterized MS patients from Germany were investigated and compared to 395 healthy control subjects. Each individual was genotyped for 22 polymorphic markers located within or close to immunorelevant candidate genes including HLA-DRB1*, T-cell receptor (TCR), cell interaction molecules, cytokines, and cytokine receptor genes. Altogether, approximately 17,000 genetic analyses were performed. Patients were grouped according to the course of MS-relapsing-remitting or chronic progressive. Most of the genetic markers were not associated with increased risk or their exact contribution was not clear (e.g., tumor necrosis factor). The relative risks for HLA-DRB1*15+ and DRB1*03+ individuals were 3.64 and 1.42, respectively. In both groups of patients, certain TCRB gene polymorphisms were risk factors. In DRB1*03+ individuals the relative risk was increased (> 22) when a specific TCRBV6S3 allele was also inherited. Furthermore, distinct linkage disequilibria of TCRBV6S1/TCRBV6S3 elements in patients and control subjects strongly suggested an additional risk factor in the TCRBV region for DRB1*15+ individuals. These findings are discussed with respect to the pathogenesis and rational approaches to the therapy of MS.

No linkage or association between multiple sclerosis and the myelin basic protein gene in affected sibling pairs

Myelin basic protein was examined as a candidate gene for susceptibility to multiple sclerosis using two adjacent amplification fragment length polymorphisms (AmpFLPs), containing seven and six highly informative alleles respectively. No allelic association was found with multiple sclerosis, comparing 77 cases and 88 controls, and there was no evidence for linkage in 73 affected sibling pairs, using the methods of identity by descent and identity by state.

The role of genetic factors in multiple sclerosis susceptibility

There has been increasing evidence that genetic factors have a role in determining susceptibility to MS. Re-examination of results from prevalence and migration surveys reveals that there remains considerable ambiguity in interpretation. Some patterns previously thought to decisively support environmental determination may still be explained, at least in part, on a genetic basis. It seems inescapable that MS is probably due to an interaction of genetic and environmental factors. It remains undetermined whether or not genes exist which are truly necessary for the development of the disease. Existing data are consistent with the notion that the study of MS susceptibility will parallel the findings in experimental models of spontaneous autoimmunity and that at very least, two genes and almost certainly several genes will be found to influence susceptibility and interact in as yet unknown ways. One of these loci appears to be the Class II MHC, although its role may be minor at the germ line level. Roles for the T-cell receptor alpha and beta loci appear to be minor and may even be non-existent in contributing to heritable susceptibility. We predict that additional loci will be identified which influence both susceptibility and outcome and will be more important. Furthermore, it is clear that the understanding of the contribution of individual susceptibility loci will continue to be difficult because of the constraints of human pedigree data. It is likely that further resolution of the questions posed above related to genetic susceptibility in MS will require multicenter collaboration.

Association studies in multiple sclerosis

In the search for candidate loci having a role in susceptibility to common diseases such as multiple sclerosis (MS), studies often look for an 'association' between one allele at a putative candidate susceptibility locus and the disease, e.g. MS. However, reproducibility of results from association studies has been difficult. In MS, despite numerous studies, association has been reproducibly confirmed only for the major histocompatibility complex, the MHC. The present paper is designed to review the allelic associations which have been reported in MS and suggest possible reasons for the difficulties in replicating these studies. We also outline some suggestions for improving the validity of future association studies in MS and in other complex traits.

The germline repertoire of T cell receptor beta-chain genes in multiple sclerosis patients from Spain

Recently several reports have described contradictory results after studying the association between restriction fragments length polymorphisms (RFLP) of T cell receptor (TcR) beta-chain genes and multiple sclerosis (MS). We studied the allelic, genotypic and haplotypic distribution of RFLPs of TcR beta chain gene segments C beta, V beta 8 and V beta 11 in 97 unrelated multiple sclerosis (MS) patients, 11 with chronic progressive MS and 86 with relapsing/remitting (R/R) MS. We found the distribution of the TcR haplotypes defined by the alleles of the three loci studied in the MS patients was significantly different from that found in control individuals. The distribution of TcR haplotypes in R/R MS patients was also different from that observed in controls. Our data suggest that the TcR beta chain gene complex contains one or more genes involved in genetic susceptibility to develop MS.

Susceptibility for multiple sclerosis is determined, in part, by inheritance of a 175-kb region of the TcR V beta chain locus and HLA class II genes

Genetic makeup thought to affect susceptibility to multiple sclerosis (MS) and current evidence suggests that multiple genes may be involved. We have mapped a potential susceptibility gene or genes in the germ-line T cell receptor (TcR) V beta region of multiple sclerosis (MS) patients. Six restriction fragment length polymorphisms (RFLPs) spanning approximately 600 kb of the TcR V beta region were used to define TcR haplotypes in 197 Caucasian controls and 83 Caucasian MS patients in the chronic progressive stage of the disease. The distribution of TcR subhaplotype frequencies was significantly different only in the approx. 175-kb region between RFLPs defined by V beta 8.1 and V beta 11. Stratification of the MS patients into HLA-DR2+ (n = 51) and HLA-DR2- (n = 32) populations demonstrated that the subhaplotype frequencies differed from the control population significantly only in the HLA-DR2+ (corrected P = 0.00007) and not in the HLA-Dr2- (corrected P = 0.46) population. Subhaplotypes which are rare in the normal population are overrepresented in the HLA-DR2+ MS patient population and confer a relative risk of 4.06. These results indicate the existence of an MS susceptibility gene within the TcR V beta region, and provide new evidence for gene complementation between a HLA class II gene and TcR V beta gene(s) in conferring susceptibility to MS.

Organization of human T-cell receptor beta-chain genes: clusters of V beta genes are present on chromosomes 7 and 9

To ascertain the extent and organization of the germ-line human T-cell receptor (TCR) beta-chain gene repertoire, beta-chain variable region (V beta) genes were mapped by pulsed-field gel electrophoresis, cosmid cloning, and in situ hybridization. Probes derived from the 24 known V beta families were mapped to a total of six Sfi I fragments in DNA samples from multiple individuals representing all possible haplotypes of TCR V- and C (constant)-region insertion/deletion-related polymorphisms. Four of the Sfi I fragments were linked to one another to develop an extended map of the TCR beta-chain gene complex previously localized to chromosome 7q35. The remaining two Sfi I fragments, containing 6 V beta genes, could not be linked to the TCR beta-chain gene complex. Using human-hamster somatic cell hybrids and in situ hybridization, these orphon genes were localized to chromosome 9p. Nucleotide sequences of the orphon V beta genes, derived from cosmid clones, were 93-97% identical to V beta genes in the TCR beta-chain gene complex. Open reading frames in three of the orphon V beta genes were intact as were the recombination signal sequences. As expected, based on their orphon status, none of the V beta genes of chromosome 9 was detected in transcripts containing C beta. These results indicate that the functional germ-line V beta repertoire in humans is substantially (10%) smaller than previously estimated.

Restriction fragment length polymorphism analysis of HLA-DR- and DQ-linked alleles in multiple sclerosis in Spain

HLA-DR allele subtypes in multiple sclerosis (MS) individuals in Spain were determined by restriction fragment length polymorphism (RFLP) analysis. The well-established association of DRw15, DQw6, Dw2 alleles and MS susceptibility was confirmed. The strength of its association, however, was relatively weak in our MS population and no involvement with any other DR allele was observed. DQw6 increase correlated with the elevation of the involved DR2 subtype. The hypothesis that MS-associated susceptibility genes may be more closely associated with the DQ than the DR region was not supported by our findings which, on the other hand, could be in concordance with the concept that multiple genes contribute to MS susceptibility.

Multiple sclerosis: an autoimmune disease of multifactorial etiology

The etiology of multiple sclerosis is linked to a variety of genetic and environmental factors. Both cell-mediated and humoral immune responses, triggered by extraneous or autoantigens, are likely to contribute to the pathogenesis of this disease. A greater insight into the fundamental cause of multiple sclerosis has been provided by the recognition that certain immune response genes are associated with an increased susceptibility to the disease. Such knowledge should provide new opportunities for selective therapeutic interventions.

Non-MHC-linked genes in autoimmune diseases

The gene responsible for the lpr mutation in MRL mice that are prone to systemic lupus erythematosus has been shown to encode the apoptosis-inducing Fas antigen, thus pointing to control of apoptosis as a major regulatory mechanism in autoimmunity. In the non-obese diabetic mouse model for insulin-dependent diabetes, four non-MHC-linked loci have been localized in the murine genome that were found to be associated with successive stages of the disease. These findings should soon have a major impact on our understanding of human autoimmune diseases.