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

Influence of Genetic Polymorphisms on Clinical Outcomes of Glatiramer Acetate in Multiple Sclerosis Patients

Multiple sclerosis (MS) is a chronic, inflammatory, demyelinating disease of autoimmune origin, in which inflammation and demyelination lead to neurodegeneration and progressive disability. Treatment is aimed at slowing down the course of the disease and mitigating its symptoms. One of the first-line treatments used in patients with MS is glatiramer acetate (GA). However, in clinical practice, a response rate of between 30% and 55% is observed. This variability in the effectiveness of the medication may be influenced by genetic factors such as polymorphisms in the genes involved in the pathogenesis of MS. Therefore, this review assesses the impact of genetic variants on the response to GA therapy in patients diagnosed with MS. The results suggest that a relationship exists between the effectiveness of the treatment with GA and the presence of polymorphisms in the following genes: CD86, CLEC16A, CTSS, EOMES, MBP, FAS, TRBC1, IL1R1, IL12RB2, IL22RA2, PTPRT, PVT1, ALOX5AP, MAGI2, ZAK, RFPL3, UVRAG, SLC1A4, and HLA-DRB1*1501. Consequently, the identification of polymorphisms in these genes can be used in the future as a predictive marker of the response to GA treatment in patients diagnosed with MS. Nevertheless, there is a lack of evidence for this and more validation studies need to be conducted to apply this information to clinical practice.

Gene expression studies in multiple sclerosis

Multiple sclerosis (MS) is a serious neurological disorder affecting young Caucasian individuals, usually with an age of onset at 18 to 40 years old. Females account for approximately 60x of MS cases and the manifestation and course of the disease is highly variable from patient to patient. The disorder is characterised by the development of plaques within the central nervous system (CNS). Many gene expression studies have been undertaken to look at the specific patterns of gene transcript levels in MS. Human tissues and experimental mice were used in these gene-profiling studies and a very valuable and interesting set of data has resulted from these various expression studies. In general, genes showing variable expression include mainly immunological and inflammatory genes, stress and antioxidant genes, as well as metabolic and central nervous system markers. Of particular interest are a number of genes localised to susceptible loci previously shown to be in linkage with MS. However due to the clinical complexity of the disease, the heterogeneity of the tissues used in expression studies, as well as the variable DNA chips/membranes used for the gene profiling, it is difficult to interpret the available information. Although this information is essential for the understanding of the pathogenesis of MS, it is difficult to decipher and define the gene pathways involved in the disorder. Experiments in gene expression profiling in MS have been numerous and lists of candidates are now available for analysis. Researchers have investigated gene expression in peripheral mononuclear white blood cells (PBMCs), in MS animal models Experimental Allergic Encephalomyelitis (EAE) and post mortem MS brain tissues. This review will focus on the results of these studies.

Revisiting the T-cell receptor alpha/delta locus and possible associations with multiple sclerosis

A role for T cells in the pathogenesis of multiple sclerosis (MS) is well supported, evidenced by myriad immunological studies, as well as the unequivocal genetic influence of the major histocompatibility complex (MHC). Despite many attempts, no convincing genetic associations have been made between T-cell receptor (TCR) gene loci and MS. However, these studies may not be definitive because of small sample sizes and under-representative marker coverage of the chromosomal regions being investigated. To explore potential roles between the TCR alpha locus and MS, we have genotyped a large family-based cohort, including 1360 affected individuals and 1659 of their unaffected first-degree relatives, at 40 single-nucleotide polymorphism (SNP) markers within the TCR alpha/delta locus. This represents the largest TCR alpha-MS study to date. From this screen, we identified three potential loci of interest in TCR alpha variable and constant gene regions using the transmission disequilibrium test. Although SNPs implicating each of these regions of interest will require genotyping in independent replication cohorts, these findings suggest a role for TCR gene polymorphisms in MS susceptibility. In the context of these findings we review the evidence.

Thinking about repairing thinking

The work of Sinden et al. suggests that it may be possible to produce improvement in the “highest” areas of brain function by transplanting brain tissue. What appears to be the limiting factor is not the complexity of the mental process under consideration but the discreteness of the lesion which causes the impairment and the appropriateness and accuracy of placement of the grafted tissue.

Therapeutic uses for neural grafts: Progress slowed but not abandoned

In spite of Stein and Glasier's justifiable conclusion that initial optimism concerning the immediate clinical applicability of neural transplantation was premature, there exists much experimental evidence to support the potential for incorporating this procedure into a therapeutic arsenal in the future. To realize this potential will require continued evolution of our knowledge at multiple levels of the clinical and basic neurosciences.

The structure, operation, and functionality of intracerebral grafts

The concept of structure, operation, and functionality, as they may be understood by clinicians or researchers using neural transplantation techniques, are briefly defined. Following Stein & Glasier, we emphasize that the question of whether an intracerebral graft is really functional should be addressed not only in terms of what such a graft does in a given brain structure, but also in terms of what it does at the level of the organism.

The NGF superfamily of neurotrophins: Potential treatment for Alzheimer's and Parkinson's disease

Stein & Glasier suggest embryonic neural tissue grafts as a potential treatment strategy for Alzheimer's and Parkinson's disease. As an alternative, we suggest that the family of nerve growth factor-related neurotrophins and their trk (tyrosine kinase) receptors underlie cholinergic basal forebrain (CBF) and dopaminergic substantia nigra neuron degeneration in these diseases, respectively. Therefore, treatment approaches for these disorders could utilize neurotrophins.

Some practical and theoretical issues concerning fetal brain tissue grafts as therapy for brain dysfunctions

Grafts of embryonic neural tissue into the brains of adult patients are currently being used to treat Parkinson's disease and are under serious consideration as therapy for a variety of other degenerative and traumatic disorders. This target article evaluates the use of transplants to promote recovery from brain injury and highlights the kinds of questions and problems that must be addressed before this form of therapy is routinely applied. It has been argued that neural transplantation can promote functional recovery through the replacement of damaged nerve cells, the reestablishment of specific nerve pathways lost as a result of injury, the release of specific neurotransmitters, or the production of factors that promote neuronal growth. The latter two mechanisms, which need not rely on anatomical connections to the host brain, are open to examination for nonsurgical, less intrusive therapeutic use. Certain subjective judgments used to select patients who will receive grafts and in assessment of the outcome of graft therapy make it difficult to evaluate the procedure. In addition, little long-term assessment of transplant efficacy and effect has been done in nonhuman primates. Carefully controlled human studies, with multiple testing paradigms, are also needed to establish the efficacy of transplant therapy.

Models of neurological defects and defects in neurological models

The transition from research to patient following advances in transplantation research is likely to be disappointing unless it includes a better understanding of critically relevant characteristics of the neurological disorder and improvements in the animal models, particularly the behavioral features. The appropriateness of the model has less to do with the species than with how the species is used.

Effects of infectious mononucleosis and HLA-DRB1*15 in multiple sclerosis

BACKGROUND

Both human leukocyte antigen (HLA)-DRB1*15 and Epstein-Barr virus infection presenting as infectious mononucleosis (IM) are recognized as risk factors for multiple sclerosis (MS). However, their combined effect and possible interaction on MS risk is not known.

OBJECTIVE

To assess the association between HLA-DRB1*15 and risk of MS in persons with and without IM.

METHODS

We compared the prevalence of DRB1*15 in MS patients with (n = 76) and without (n = 1,836) IM with the corresponding distributions in blood donors with (n = 62) and without (n = 484) IM histories. This allowed us to estimate the relative risk of MS associated with DRB1*15 in the presence and absence, respectively, of previous IM. We then estimated the interaction between DRB1*15 and IM as the ratio of the two individual odds ratios.

RESULTS

In IM-naïve individuals, DRB1*15 carried a 2.4-fold (95% confidence interval [CI], 2.0-3.0) increased MS risk. In contrast, among persons with IM history, DRB1*15 was associated with a 7.0-fold (95% CI, 3.3-15.4) increased MS risk. Thus, the MS risk conferred by HLA-DRB1*15 was 2.9 (95% CI, 1.3-6.5)-fold stronger in the presence than in the absence of IM. Combined with previous results, this result indicates that DRB1*15-positive persons with a history of IM may be at a 10.0-fold (95% CI, 6.0-17.9) increased risk of MS compared with persons who are DRB1*15 and IM-naïve.

CONCLUSION

DRB1*15 and IM may act in synergy causing MS.

HLA-DR15 haplotype and multiple sclerosis: a HuGE review

An association between multiple sclerosis (MS) and the human leukocyte antigen (HLA) complex, a dense cluster of genes on the short arm of chromosome 6, was first noted over 30 years ago. In Caucasian populations of Northern European descent, the DR15 haplotype (DRB1*1501-DQA1*0102-DQB1*0602) has been hypothesized to be the primary HLA genetic susceptibility factor for MS. However, studies of other populations have produced varying results. Thus, the authors reviewed the literature for articles on the association between the DR15 haplotype and MS. They identified 72 papers meeting the inclusion criteria: human genetic studies written in English that were published between 1993 and 2004 and that reported allele frequencies for HLA-DRB1*1501, HLA-DQA1*0102, or HLA-DQB1*0602 or the frequency of the DRB1*1501-DQA1*0102-DQB1*0602 haplotype. Most of the studies identified used a case-control design (n = 60), while the remainder used a family-based design (n = 22). In most of these papers, investigators reported a higher frequency of the DR15 haplotype and/or its component alleles among MS cases than among controls. However, the authors' confidence in these results is tempered by factors related to study design that may have biased the outcomes.

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.

Genetics of multiple sclerosis

Multiple sclerosis (MS) is probably aetiologically heterogeneous. Systematic genetic epidemiological and molecular genetic studies have provided important insights. Both genetic and non-genetic (environment, stochastic) factors may be involved in susceptibility as well as outcome, but we have yet to understand their relative roles. Any environmental factor is likely to be ubiquitous and act on a population-basis rather than within the family microenvironment. Taken together, the results of genome screening studies provide strong evidence for exclusion of a major locus in MS. There are, however, many genes that seem to be associated with MS. These include, but are in no way limited to, HLA classes I and II, T-cell receptor beta, CTLA4, ICAM1, and SH2D2A. The future of MS genetics, as for most common complex disorders, will be dependent on the resources available, ranging from biological samples and comprehensive databases of clinical and epidemiological information to the development of new technologies and statistical methods.

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.

The genetics of multiple sclerosis. A review

Multiple sclerosis (MS) is characterized by chronic inflammation and demyelination in the central nervous system (CNS). Although the etiology of MS is unknown, both genetic and environmental contributions to the pathogenesis are inferred from epidemiologic studies. Geographic distributions and epidemics of MS and data from migration studies provide evidence for some, thus far unidentified, environmental effects. The co-occurrence of MS with high and low frequencies in ethnic groups often sharing an environment, the increased recurrence rate in families, and the high concordance rate among identical twins point to inheritable determinants of susceptibility. Based on the autoimmune hypothesis of demyelination, genetic studies sought associations between MS and polymorphic alleles of candidate genes which regulate either the immune response or myelin production. The most consistent finding in case-control studies was the association with the major histocompatibility complex (MHC) (also called human leukocyte antigen--HLA) class II, DR15, DQ6, Dw2 haplotype. Studies on other gene products encoded within or close to the MHC complex on chromosome 6p21.3 (e.g., HLA DP, complement components, transporter proteins, tumor necrosis factor, and myelin-oligodendrocyte glycoprotein) resulted in conflicting observations in different patient populations. The potential contribution of polymorphic alleles within the genes of the T-cell receptor alpha beta chains, immunoglobulins, cytokines, and oligodendrocyte growth factors or their receptors to MS susceptibility either remains equivocal or is rejected. Studies on families with multiple affected members have revealed that MS is a complex trait, that the contribution of individual genes to susceptibility is probably small, and that differences are possible between familial and sporadic forms. The development of molecular and computer technologies have facilitated the performance of comprehensive genomic scans in multiplex families, which have confirmed the possible linkage of multiple loci to susceptibility, each with a minor contribution. Several provisional sites were reported, but only 6p21 (MHC complex), 5p14, and 17q22 were positive in more than one study. The British update demonstrated segregation among regions of interest depending on DR15 sharing, and excluded a gene of major effect from 95%, and one with a moderate effect from 65% of the genome. The extended study by the US collaboration group revealed that the MHC linkage was limited to families segregating HLA DR2 alleles, which suggested that linkage to the MHC is related to the HLA DR2 association, and that sporadic and familial MS share at least one common susceptibility marker. Further identification of MS susceptibility loci may involve additional family sets, more polymorphic markers, and the exploration of telomeric chromosomal regions. Data from these studies may further elucidate pathogenic mechanisms of MS.

Association of HLA and T-cell receptor gene polymorphisms with Semple rabies vaccine-induced autoimmune encephalomyelitis

Semple rabies vaccine is derived from brain tissue infected with rabies virus that is subsequently inactivated with phenol. Semple rabies vaccine-induced autoimmune encephalomyelitis (SAE) occurs in 1 in 220 immunized individuals. The immune response to myelin basic protein and pathological changes of demyelination in SAE suggest that this disease is the human homologue of experimental autoimmune encephalomyelitis (EAE). SAE and EAE are frequently studied as models for the human demyelinating disease multiple sclerosis. Major histocompatibility complex (MHC) class II and T-cell receptor (TCR) gene polymorphisms play important roles in rodent susceptibility to EAE and were analyzed to determine if the same was true in humans with SAE. HLA-DRB1, HLA-DQB1, and TCRBV gene polymorphisms were studied in Thai individuals with SAE (n = 18), with vaccination without neurological complications (n = 43), and without vaccination (n = 140). The allele frequencies of HLA-DR9 (DRB1*0901) and HLA-DR17 (DRB1*0301) were increased in SAE patients (DR9 = 22%, DR17 = 14%) compared with vaccinated controls (DR9 = 13%, DR17 = 6%) and with unvaccinated controls (DR9 = 9%, DR17 = 4%). The allele frequency of HLA-DQ7 (DQB1*0301) was decreased in SAE patients (8%) compared with vaccinated controls (15%) and with unvaccinated controls (25%). These susceptibilities are distinct from those associated with multiple sclerosis. The frequencies of TCRBV alleles and haplotypes were similar in SAE patients and vaccinated controls. These data suggest that genetic susceptibility associated with MHC class II alleles may have a role in the pathogenesis of SAE and its mechanism may be different from those involved in multiple sclerosis.

Neurotrophic ACTH4-9 analogue therapy normalizes electroencephalographic alterations in chronic experimental allergic encephalomyelitis

Chronic experimental allergic encephalomyelitis (CEAE) is an established experimental model for multiple sclerosis (MS). The demyelinating lesions in the white matter of the central nervous system observed in CEAE and in MS are accompanied by various neurophysiological alterations. Among the best defined electrophysiological abnormalities are the changes in event-related potentials, in particular evoked potentials involving the spinal cord, i.e. motor and sensory evoked potentials. Less familiar are the changes observed in the electroencephalogram of CEAE-affected animals, which are also encountered in the human equivalent, MS. In the present experiment we evaluated the therapeutic value of a neurotrophic peptide treatment [H-Met(O2)-Glu-His-Phe-D-Lys-Phe-OH, an ACTH4-9 analogue] and its effect on the delayed flash visual evoked potentials (VEP) and power spectra of the electroencephalogram, during a 17-week follow-up of CEAE. CEAE animals treated with the neurotrophic peptide were protected against the development of neurological symptoms during the course of the demyelinating syndrome. VEPs of animals suffering from CEAE showed a delay of the latencies of the late components which was significantly counteracted by peptide treatment. The peak-to-peak amplitude of the VEP afterdischarge recorded from CEAE animals was significantly increased during the course of CEAE and correlated closely with the progression of the myelinopathy. Furthermore, CEAE animals showed an increase of electroencephalogram (EEG) beta activity of up to 500% as compared with the age-matched control group. This increase in beta power mainly consisted of a prevailing 20-21 Hz peak, a frequency that normally is not dominant in control EEG recordings of the rat during passive wakefulness. All these electrophysiological phenomena were absent in ACTH4-9 analogue-treated animals. The present findings underscore the potential importance of a neurotrophic peptide treatment in the pharmacotherapy of central demyelinating syndromes, and possibly of MS.

Molecular analysis of HLA class I (HLA-A and -B) and HLA class II (HLA-DRB1) genes in Japanese patients with multiple sclerosis (Western type and Asian type)

The types of HLA-A, -B and -DRB1 genes were studied in 146 Japanese patients with multiple sclerosis (MS) using polymerase chain reaction-sequence-specific oligonucleotide probe analysis. Fifty-seven patients who displayed selective clinical involvement of the optic nerve and spinal cord were classified as having Asian type MS. The other 89 patients had disseminated central nervous system involvement and were classified as having Western type MS. The frequency of HLA-B*5101 was increased in both types of MS patients compared with controls. The frequency of HLA-DRB1*1501 was increased in Western type MS and the frequency of HLA-DRB1*0802 was increased in Asian type MS compared to controls. After correction of P values, the association of Western type MS patients with HLA-DRB1*1501 was statistically significant (Pc=0.0003) whereas other HLA alleles showed no significant association. These results suggest that HLA class I (HLA-A and -B) alleles may not contribute to a strong susceptibility to MS in Japanese compared to HLA class II (HLA-DRB1) alleles.

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.

HLA associations with multiple sclerosis in the Canary Islands

The study of small island populations has proved informative with respect to the epidemiology and genetics of many complex traits including multiple sclerosis. The class II major histocompatibility antigen DR15 is associated with multiple sclerosis in all groups except Sardinians, where the primary association is with DR4. We compared HLA-DR and -DQ allele frequencies in a representative sample of patients with multiple sclerosis from the Canary Islands with appropriate controls. There was a significant association with DR15 (patients 21/53: 40%: controls 11/55; 20%: chi2=4.09; pc=0.04; relative risk [RR]=1.98). DRB1*1501-DRB5*0101 was present in 17/53 (32%) patients in whom sub-types could be identified compared with 6/55 (11%) controls (chi2=7.21; pc=< 0.01; RR=2.94). All DR15 positive controls carried the DQA1*0102, DQB1*0602 haplotype whereas this was only present in 26/30 patients, suggesting that the primary association is with HLA-DR and not -DQ. We also found a significant increase in HLA-DR4 (16/53 [30%] in patients compared with 7/55 [13%] in controls; pc=0.05). This study contributes a new point on the immunogenetic map of multiple sclerosis in Europe, confirming the primary DR15 association with multiple sclerosis in a previously unstudied population but again highlighting the importance of DR4 in Mediterranean peoples.

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.

The CCR5 deletion mutation fails to protect against multiple sclerosis

Recent advances in the understanding and identification of chemokines and their receptors have provided evidence for their consideration as candidate loci with respect to genetic susceptibility/resistance to MS. Increased levels of the chemokine, macrophage inflammatory protein (MIP)-1 alpha, have been demonstrated in the cerebrospinal fluid of both patients with MS and mice with EAE, and anti-MIP-1 alpha antibodies have been shown to prevent EAE. Recently, a common deletion mutation in the gene for the major receptor for MIP-1 alpha, chemokine receptor 5 (CCR5) has been described. Homozygotes for the mutation fail to express this receptor. Moreover, homozygotes are highly protected against HIV infection this has potential implications for the cell entry of infectious agents in other multifactorial disease where a viral component may be involved. In view of these aspects, a group of 120 unrelated Australian relapsing remitting MS and 168 unrelated control subjects were screened for the CCR5 delta 32 mutation. There was no significant difference in the allele frequency of CCR5 delta 32 gene between the MS patients (0.1125) and the control population (0.0921). The presence of two CCR5 delta 32 homozygotes in the MS patients indicates that the absence of CCR5 is not protective against MS. These data suggest that CCR5 is not an essential component in MS expression, though this may be due to redundancy in the chemokine system where different chemokine receptors may substitute for CCR5 when it is absent.

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.

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.

Limited junctional diversity of V delta 5-J delta 1 rearrangement in multiple sclerosis patients

T-cell receptor (TCR) delta gene repertoire, as assessed by V delta-J delta rearrangements, has been analyzed in nine multiple sclerosis (MS) cases and in 30 healthy individuals by seminested PCR technique. Among the V delta-J delta junctional diversities studied, the most striking result has been observed in V delta 5-J delta 1 rearrangement. The detection of repeated V delta 5-J delta 1 nucleotide sequences in all analyzed clones from seven out of nine patients studied proved the monoclonal nature of gamma delta T-cells with V delta 5-J delta 1 rearrangement. The clonal nature of this rearrangement proved by PAGE and sequencing analysis may suggest an antigen-driven expansion of gamma delta T cells and argues for a significant role of gamma delta T-cells with V delta 5-J delta 1 rearrangement in MS pathogenesis. However, it cannot be excluded that clonal expansion of these lymphocytes may represent secondary change to central nervous system damage.

Analysis of germline and expressed T cell receptor variable region genes in Crohn's disease

A possible role of the T cell receptor genes in the pathogenesis of Crohn's disease was investigated by 1) comparison of restriction fragment length polymorphisms at the T cell receptor beta chain locus in 64 Crohn's patients and 64 normal controls; 2) semi-quantitative polymerase chain reaction analysis of T cell receptor beta and alpha chain variable region gene expression by lamina propria lymphocytes from resected segments of diseased terminal ileum. We found no association between any of the restriction fragment length polymorphisms and Crohn's disease using polymorphic markers spanning the T cell receptor beta chain locus. Analysis of T cell receptor V beta and V alpha gene expression showed that expression of T cell receptor V region families in terminal ileum lymphocytes from patients with active Crohn's disease was indistinguishable from the lymphocytes found in normal terminal ileum. These data fail to support susceptibility to Crohn's disease being associated with the T cell beta chain antigen receptor genotype. No restricted or dominant T cell receptor variable region gene expression was found in Crohn's disease tissue, compared to normal terminal ileum.

Characterization of the mitochondrial DNA in patients with multiple sclerosis

Mitochondrial DNA (mtDNA) abnormalities with primary pathogenic significance for optic nerve atrophy have been detected in inflammatory demyelinating conditions indistinguishable from multiple sclerosis (MS). However, the degree of involvement of mtDNA alterations in the pathogenesis of MS is not clear. To further clarify this question, we sequenced the entire mtDNA in three MS patients. A number of nucleotide alterations were defined relative to the standard mtDNA sequence in each patient. After excluding the silent mutations and common polymorphisms, eight unusual mtDNA variants within the ribosomal (r) RNA, transfer (t) RNA or protein encoding regions were identified and characterized. Two mutations remained as putative MS related alterations after screening a population of 49 patients and 63 controls for the presence of these mutations. An A to G transition at nucleotide (nt) 13966 causing a threonine to phenylalanine exchange in a non-conserved region of the ND-5 was detected in two independent MS patients and in none of the sixty-three controls or in any of the large control population in the literature. The second mutation of interest at 14798 is a T to C transition changing a phenylalanine to leucine in a relatively conserved domain of the cytochrome b. Although it is a known polymorphism, a tendency for prominent optic nerve involvement was observed among patients carrying this mutation. As we have performed the first complete mtDNA sequence analysis on MS patients, we conclude that MS may occur without mtDNA abnormalities of primary pathogenic significance. However, contribution of the mtDNA to genetic susceptibility or phenotypic presentation of MS is possible in certain subgroups of patients, and merits further investigation.

A genome screen in multiple sclerosis reveals susceptibility loci on chromosome 6p21 and 17q22

The population prevalence of multiple sclerosis is 0.1%; however, the risk of the disease in the siblings of affected individuals is very much higher at 3-5%. The importance of genetic factors in accounting for this increased risk is confirmed by the results of twin and adoption studies. Despite the evidence for a strong genetic effect, a weak major histocompatibility complex (MHC) association is the only consistently observed feature in the genetics of multiple sclerosis. Other candidates have been proposed, including genes encoding the immunoglobulin heavy chain, T cell receptor beta chain and APOC2, but none has yet been confirmed. Evidence for linkage and association to the myelin basic protein gene has been reported in a genetically isolated Finnish population, but it has not been possible to reproduce these results in other populations. We used a two-stage approach to search the human genome for the genes causing susceptibility to multiple sclerosis. Two principal regions of linkage are identified, chromosomes 17q22 and 6p21 (MHC). Our results are compatible with genetic models involving epistatic interaction between these and several additional genes.

A full genome search in multiple sclerosis

The aetiology of multiple sclerosis (MS) is uncertain. There is strong circumstantial evidence to indicate it is an autoimmune complex trait. Risks for first degree relatives are increased some 20 fold over the general population. Twin studies have shown monozygotic concordance rates of 25-30% compared to 4% for dizygotic twins and siblings. Studies of adoptees and half sibs show that familial risk is determined by genes, but environmental factors strongly influence observed geographic differences. Studies of candidate genes have been largely unrewarding. We report a genome search using 257 microsatellite markers with average spacing of 15.2 cM in 100 sibling pairs (Table 1, data set 1 - DS1). A locus of lambda>3 was excluded from 88% of the genome. Five loci with maximum lod scores (MLS) of >1 were identified on chromosomes 2, 3, 5, 11 and X. Two additional data sets containing 44 (Table 1, DS2) and 78 sib pairs (Table 1, DS3) respectively, were used to further evaluate the HLA region on 6p21 and a locus on chromosome 5 with an MLS of 4.24. Markers within 6p21 gave MLS of 0.65 (non-significant, NS). However, D6S461, just outside the HLA region, showed significant evidence for linkage disequilibrium by the transmission disequilibrium test (TDT), in all three data sets (for DS1 chi2 = 10.8, adjusted P < 0.01)(DS2 and DS3 chi2 = 10.9, P < 0.0005), suggesting a modest susceptibility locus in this region. On chromosome 5p results from all three data sets (222 sib pairs) yielded a multipoint MLS of 1.6. The results support genetic epidemiological evidence that several genes interact epistatically to determine heritable susceptibility.

A complete genomic screen for multiple sclerosis underscores a role for the major histocompatability complex. The Multiple Sclerosis Genetics Group

Multiple sclerosis (MS), an inflammatory autoimmune demyelinating disorder of the central nervous system, is the most common cause of acquired neurological dysfunction arising in the second to fourth decades of life. A genetic component to MS is indicated by an increased relative risk of 20-40 to siblings compared to the general population (lambda s), and an increased concordance rate in monozygotic compared to dizygotic twins. Association and/or linkage studies to candidate genes have produced many reports of significant genetic effects including those for the major histocompatability complex (MHC; particularly the HLA-DR2 allele), immunoglobulin heavy chain (IgH), T-cell receptor (TCR) and myelin basic protein (MBP) loci. With the exception of the MHC, however, these results have been difficult to replicate and/or apply beyond isolated populations. We have therefore conducted a two-stage, multi-analytical genomic screen to identify genomic regions potentially harbouring MS susceptibility genes. We genotyped 443 markers and 19 such regions were identified. These included the MHC region on 6p, the only region with a consistently reported genetic effect. However, no single locus generated overwhelming evidence of linkage. Our results suggest that a multifactorial aetiology, including both environmental and multiple genetic factors of moderate effect, is more likely than an aetiology consisting of simple mendelian disease gene(s).

Genetics of demyelinating diseases

Multiple sclerosis (MS), the prototypic demyelinating disease in humans, is the most common cause of acquired neurological dysfunction arising between early to mid adulthood. MS is an inflammatory disorder and is believed to result from an autoimmune response, directed against myelin proteins and perhaps other antigens, resulting in demyelination and dense astrogliosis. A genetic component in MS is indicated by an increased relative risk to siblings compared to the general population (lambda s) of 20-40, and an increased concordance rate in monozygotic compared to dizygotic twins. Association and/or linkage studies to candidate genes have yielded a considerable number of reports showing significant genetic effects for the major histocompatibility complex (MHC), immunoglobulin heavy chain, T cell antigen receptor, and myelin basic protein loci. With the exception of the MHC, however, these results have been difficult to replicate or apply beyond isolated populations. Recently, a multi-analytical genomic screen effort was completed to identify genomic regions potentially harboring MS susceptibility genes. Nineteen such regions were identified. The data confirm the reported genetic effect of the MHC region. However, no single locus generated overwhelming evidence of linkage. These results suggest a multifactorial etiology, including both environmental and multiple genetic factors of moderate effect.

The evolutionary relationship among Caucasian MS patients and controls

Previous observations suggest that the mitochondrial (mt)DNA may confer susceptibility to multiple sclerosis (MS). However, the proportion of affected individuals and the range of contributing mtDNA abnormalities are unknown. To help clarify this question, we analyzed the first hypervariable D-loop sequences of the mtDNA in a group of randomly selected Caucasian MS patients, in MS patients with prominent optic neuritis (PON) and in controls. Phylogenetic analysis of these D-loop sequences revealed that individuals in both groups of patients are generally scattered in the Caucasian phylogeny. However, a small cluster of unrelated MS patients identified by this analysis suggests that a maternal lineage with MS relevant mtDNA sequences may exist, and merits a more comprehensive study.

Mitochondrial DNA mutations in multiple sclerosis

The presence of mitochondrial DNA mutations, including eight of those frequently associated with Leber's hereditary optic neuropathy (LHON), was investigated by sequencing and restriction endonuclease analysis in randomly selected patients with MS. Class I LHON mutations with primary pathogenic significance for blindness were not detected in any of the MS patients studied. A trend was observed for higher frequency of class II LHON mutations with unknown pathogenic significance in the MS patients than in the controls. Specifically, the mutation at position 4216 and its associated simultaneous mutations occurred with a higher frequency. Eleven of the 53 patients (20.8%) were positive for at least two (4216 and 4917 or 13,708) or three (4216, 13,708, 15,257) simultaneous class II LHON mutations, while 7 of the 74 controls (9.5%) carried simultaneous mutations (P = 0.036). Earlier studies reported the occurrence of either the 11,778 or 3460 LHON type mutations in MS patients with a positive LHON pedigree and/or with a disease course predominantly involving the optic nerves. The mutations we detected did not correlate with the severity of visual loss in either LHON or MS, rather they seemed to be present in randomly selected MS patients. We conclude that the mutations with primary pathogenic significance for blindness are not shared between LHON and randomly selected MS. However, the presence of further mitochondrial mutations cannot be excluded in MS. The increased incidence of the simultaneous class II LHON mutations in MS patients (and LHON) vs controls may indicate that certain sets of mitochrondrial DNA mutations/variants are associated with and predispose to MS, a possibility which needs to be investigated further. Alternatively, a biological disadvantage may be associated with the coexistence of the mutations detected.

The spinal cord as an alternative model for nerve tissue graft

The spinal cord provides an alternative model for nerve tissue grafting experiments. Anatomo-functional correlations are easier to make here than in any other region of the CNS because of a direct implication of spinal cord neurons in sensorimotor activities. Lesions can be easily performed to isolate spinal cord neurons from descending inputs. The anatomy of descending monoaminergic systems is well defined and these systems offer a favourable paradigm for lesion-graft experiments.

Multiple obstacles to gene therapy in the brain

Neuwelt et al. have proposed gene-transfer experiments utilizing an animal model that offers many important advantages for investigating the feasibility of gene therapy in the human brain. A variety of tissues concerning the viral vector and mode of delivery of the corrective genes need to be resolved, however, before such therapy is scientifically supportable.

Principles of brain tissue engineering

It is often presumed that effects of neural tissue transplants are due to release of neurotransmitter. In many cases, however, effects attributed to transplants may be related to phenomena such as trophic effects mediated by glial cells or even tissue reactions to injury. Any conclusion regarding causation of graft effects must be based on the control groups or other comparisons used. In human clinical studies, for example, comparing the same subject before and after transplantation allows for many interpretations of the causes of clinical changes.

Lessons on transplant survival from a successful model system

Studies on the snailMelampusreveal that connectivity is crucial to the survival of transplanted ganglia. Transplanted CNS ganglia can innervate targets or induce supernumerary structures. Neuron survival is optimized by the neural incorporation that occurs when a transplanted ganglion is substituted for an excised ganglion. Better provision for the trophic requirements of neurons will improve the success of mammalian fetal transplants.

Repairing the brain: Trophic factor or transplant?

Three experiments on neural grafting with adult rat hosts are described. Working memory impairments were produced by lesioning the hippocampus or severing its connections with the septum by ablating the fimbria-fornix. The results suggest that the survival and growth of a neural graft, whether an autograft or a xenograft, is not a necessary condition for functional recovery on a task tapping working memory.

Will brain tissue grafts become an important therapy to restore visual function in cerebrally blind patients?

Grafting embryonic brain tissue into the brain of patients with visual field loss due to cerebral lesions may become a method to restore visual function. This method is not without risk, however, and will only be considered in cases of complete blindness after bilateral occipital lesions, when other, risk-free neuropsychological methods fail.

Difficulties inherent in the restoration of dynamically reactive brain systems

The responses displayed by an injured or diseased nervous system are complex. Some of the responses may effect a functional reorganization of the affected neural circuitry. Strategies aimed at the restoration of function, whether or not these involve transplantation, need to recognize the innate reactive capacity of the nervous system to damage. More successful strategies will probably incorporate, rather than ignore, the adaptive responses of the compromised neural systems.

Elegant studies of transplant-derived repair of cognitive performance

Cholinergic-rich grafts have been shown to be effective in restoring maze-learning deficits in rats with lesions of the forebrain cholinergic projection system. However, the relevance of those studies to developing novel therapies for Alzheimer's disease is questioned.