A study of the HLA-DR region in clinical subgroups of multiple sclerosis and its influence on prognosis

Human Leukocyte Antigen Genotype as a Marker of Multiple Sclerosis Prognosis

OBJECTIVE

In a previous pilot monocentric study, we investigated the relation between human leukocyte antigen (HLA) genotype and multiple sclerosis (MS) disease progression over 2 years. HLA-A*02 allele was correlated with better outcomes, whereas HLA-B*07 and HLA-B*44 were correlated with worse outcomes. The objective of this extension study was to further investigate the possible association of HLA genotype with disease status and progression in MS as measured by sensitive and complex clinical and imaging parameters.

METHODS

Hundred and forty-six MS patients underwent HLA typing. Over a 4-year period of follow-up, we performed three clinical and magnetic resonance imaging (MRI) assessments per patient, which respectively included Expanded Disability Status Scale, Multiple Sclerosis Severity Scale, Timed-25-Foot-Walk, 9-Hole Peg Test, Symbol Digit Modalities Test, Brief Visual Memory Test, California Verbal Learning Test-II, and whole-brain atrophy, fluid-attenuated inversion recovery (FLAIR) lesion volume change and number of new FLAIR lesions using icobrain. We then compared the clinical and MRI outcomes between predefined HLA patient groups.

RESULTS

Results of this larger study with a longer follow-up are in line with what we have previously shown. HLA-A*02 allele is associated with potentially better MS outcomes, whereas HLA-B*07, HLA-B*44, HLA-B*08, and HLA-DQB1*06 with a potential negative effect. Results for HLA-DRB1*15 are inconclusive.

CONCLUSION

In the era of MS treatment abundance, HLA genotype might serve as an early biomarker for MS outcomes to inform individualized treatment decisions.

HLA genotype as a marker of multiple sclerosis prognosis: A pilot study

OBJECTIVE

The identification of a biomarker with prognostic value is an unmet need in multiple sclerosis (MS). The objective of this study was to investigate a possible association of HLA genotype with disease status and progression in MS, based on comprehensive and sensitive clinical and magnetic resonance imaging (MRI) parameters to measure disease effects.

METHOD

A total of 118 MS patients (79 females, 39 males) underwent HLA typing. Patient MS status was assessed at two time points in a 2-year interval, based on clinical scores (including EDSS, MSSS, T25FW, 9-HPT, SDMT, BVMT, CVLT-II) and MRI evaluations. Quantitative brain MRI values were obtained for whole brain atrophy, FLAIR lesion volume change and number of new lesions using MSmetrix. Predefined HLA patient groups were compared as of disease status and progression. Global assessment was achieved by an overall t-statistic and assessment per measurement by a Welch test and/or Mann Whitney U test. The effects of multiple covariates, including age, gender and disease duration as well as scan parameters, were also evaluated using a regression analysis.

RESULTS

The HLA-A*02 allele was associated with better outcomes in terms of MSSS, EDSS and new lesion count (Welch test p-value<0.05). The HLA-B*07 and HLA-B*44 alleles showed a global negative effect on disease status, although none of the measurements reached significance (p-value<0.05). Results for the HLA-DRB1*15, HLA-DQB1*06 and HLA-B*08 alleles were inconclusive. The influence of the confounding variables on the statistical analysis was limited.

[Primary-progressive multiple sclerosis as an atypical demyelinating process]

This article presents an overview of current data on primary-progressive multiple sclerosis (MS). In this aspect, the authors consider its characteristics in comparison to other MS forms as well as possible markers of the disease, criteria of diagnosis and therapeutic options in the present and the future times.

Vitamin D receptor biochemical and genetic profiling and HLA-class II genotyping among Lebanese with multiple sclerosis - A pilot study

BACKGROUND

Multiple sclerosis (MS) is an autoimmune demyelinating disease affecting mostly young adult females with multifactorial etiology. Recent studies suggested that adequate vitamin D levels may lower the risk of developing MS.

OBJECTIVES

Our aim was to explore the relationship between vitamin D receptor (VDR) polymorphism, HLA-DR locus genotype, and serum vitamins D and A levels in the Lebanese population.

METHODS

Fifty MS patients were recruited for this study. The control group consisted of 48 healthy and 51 patients with other neurological disorders (non-MS). Biochemical analysis included serum 25 hydroxyvitamin D (25OHD) and vitamin A. Molecular analysis targeted VDR genotypes (ApaI, TaqI and BsmI) and low resolution HLA typing for DRB1 locus.

RESULTS

Healthy and non-MS groups had comparable parameters and were combined into one control group. No significant differences were found between MS and control groups for VDR genotypes. The frequency of HLA-DRB1*15 was significantly higher in MS patients (22%) compared to controls (8%) (p=0.018). Odds ratio for MS in the presence of DRB1*15 allele was 3.21 (p=0.018). Cosegregation with A (ApaI) and b (BsmI) alleles did not influence the risk for MS. 25OHD levels were significantly higher in MS patients compared to controls (p=0.002), due to more frequent oral supplementation (p=0.005). Vitamin A levels were comparable between the two groups. When all parameters were included in a logistic regression model adjusted for supplementation, only HLA-DRB1*15 (OR=3.42; p=0.027) contributed significantly to MS risk.

CONCLUSION

There was no association between serum vitamin D or A or VDR genotypes and MS. HLA-DRB1*15 was the major factor imposing more than 3 folds greater risk for developing MS among Lebanese.

The Role of HLA in MS Susceptibility and Phenotype

One of the most consistent findings in multiple sclerosis (MS) is that development of MS is linked with carriage of the class II human leucocyte antigen (HLA) molecule HLA-DRB1*15:01; around 60 % of Caucasian MS patients carry this allele compared to 25-30 % of ethnically matched healthy individuals. However, other HLA molecules have also been linked to the development of MS. In this chapter, the association between different HLA types and susceptibility to MS will be reviewed, and other linkages between the carriage of specific HLA molecules and clinical and experimental findings in MS will be considered.

Genetics of primary progressive multiple sclerosis

Multiple sclerosis (MS) patients are classified as either having relapsing onset or progressive onset disease, also known as primary progressive MS (PPMS). Relative to relapsing onset patients, PPMS patients are older at disease onset, are equally likely to be men or women, and have more rapid accumulation of disability that does not respond well to treatments used in relapsing onset MS. Although estimates vary, 5-15% of all MS patients have a PPMS disease course. Genetic variance is a proposed determinant of MS disease course. If distinct genes associated with PPMS were identified study of these genes might lead to an understanding of the biology underlying disease progression and neural degeneration that are the hallmarks of PPMS. These genes and their biological pathways might also represent therapeutic targets. This chapter systematically reviews the PPMS genetic literature. Despite the intuitively appealing notion that differences between PPMS and relapsing onset MS are due to genetics, definite differences associated with these phenotypes at the major histocompatibility complex or elsewhere in the genome have not been found. Recent large-scale genome wide screens identified multiple genes associated with MS susceptibility outside the MHC. The genetic variants identified thus far make only weak individual contributions to MS susceptibility. If the genetic effects that contribute to the differences between PPMS and relapsing MS are similar in magnitude to those that distinguish MS from healthy controls then, given the relative scarcity of the PPMS phenotype, very large datasets will be needed to identify PPMS associated genes. International collaborative efforts could provide the means to identify such genes. Alternately, it is possible that factors other than genetics underlie the differences between these clinical phenotypes.

Association between multiple sclerosis risk-associated SNPs and relapse and disability--a prospective cohort study

BACKGROUND

The modulating effects of the multiple sclerosis (MS) risk-associated single-nucleotide polymorphisms (SNPs) on MS clinical course are not well established.

OBJECTIVES

The objective of this paper is to investigate whether known MS risk-associated SNPs were associated with clinical course, and whether these SNPs modified the 25(OH)D-relapse association.

METHODS

Using a prospective cohort of 141 participants with relapsing-remitting MS and genotype data followed between 2002 and 2005, genotype-vitamin D interactions and the genetic predictors of relapse were assessed using survival analysis, and genetic predictors of 25(OH)D and disability progression were evaluated by multilevel mixed-effects linear regression.

RESULTS

While no SNP reached statistical significance after multiple testing, five SNPs were associated with relapse, with significant cumulative genotype risk effects and two demonstrated significant allele dose-response. Two SNPs altered the 25(OH)D-relapse association with significant allele dose-response. Five SNPs modified levels of 25(OH)D, with significant cumulative genotype 'risk' effect, and three demonstrated significant allele dose-response. We found no consistent evidence for an association between any SNPs and disability.

CONCLUSIONS

Our study provides evidence for an association between known MS risk-associated SNPs and relapse. Our findings indicate gene-environment interactions may be an important mechanism on MS clinical course, and provide support for the role of vitamin D in MS relapse.

A genome-wide association study in progressive multiple sclerosis

Background: The role played by genetic factors in influencing the clinical course of multiple sclerosis (MS) is not yet well established.

Objective: We aimed to identify genetic variants associated with progressive MS (PrMS).

Methods: We conducted a genome-wide association study (GWAS) in 197 patients with PrMS and 234 controls of Italian origin. We tested the top 20 single nucleotide polymorphisms (SNPs) with suggestive evidence of association ( p-value<10−4) in two independent sets of primary progressive MS cases and controls.

Results: We identified a risk-associated SNP in the HLA region in linkage disequilibrium (LD) with DRB1*1501 and DQB*0602 loci, with genome-wide significance (rs3129934T, pcombined=6.7×10-16, OR=2.34, 95% CI=1.90–2.87), and a novel locus on chromosome 7q35 with suggestive evidence of association (rs996343G, pcombined=2.4×10-5, OR=0.70, 95% CI=0.59–0.83) which maps within a human endogenous retroviral (HERV) element. The new locus did not have a ‘ cis’ effect on RNA expression in lymphoblastic cell lines, but pathway analyses of ‘ trans’ effects point to an expression regulation of genes involved in neurodegeneration, including glutamate metabolism ( p<0.01) and axonal guidance signalling ( p<0.02).

Conclusions: We have confirmed the established association with the HLA region and, despite the low statistical power of the study, we found suggestive evidence for association with a novel locus on chromosome 7, with a putative regulatory role.

HFE gene polymorphisms and severity in Portuguese patients with multiple sclerosis

BACKGROUND

High iron concentrations have been reported in oligodendrocytes, myelin and macrophages in multiple sclerosis (MS) lesions. It has been proposed that HFE gene polymorphisms could have a role in MS.

METHODS

The C282Y and H63D HFE variants frequencies were determined in 373 patients with MS and compared with a normal population.

RESULTS

No significant association was found between HFE polymorphisms and disease susceptibility. An analysis of the association of genotypes with disease severity was performed, and the C282Y allele was more frequent in the aggressive group.

CONCLUSIONS

Patients carrying the C282Y variant seem to have a worse prognosis.

Demographic, genetic, and environmental factors that modify disease course

As with susceptibility to disease, it is likely that multiple factors interact to influence the phenotype of multiple sclerosis and long-term disease outcomes. Such factors may include genetic factors, socioeconomic status, comorbid diseases, and health behaviors, as well as environmental exposures. An improved understanding of the influence of these factors on disease course may reap several benefits, such as improved prognostication, allowing us to tailor disease management with respect to intensity of disease-modifying therapies and changes in specific health behaviors, in the broad context of coexisting health issues. Such information can facilitate appropriately adjusted comparisons within and between populations. Elucidation of these factors will require careful study of well-characterized populations in which the roles of multiple factors are considered simultaneously.

HLA associations with multiple sclerosis in Greece

BACKGROUND

Multiple sclerosis (MS) is a demyelinating inflammatory disease of the central nervous system originated by a complex interplay of environmental and genetic factors. The association of MS with the human leukocyte antigen (HLA) class II alleles was investigated in MS patients in northwest Greece, in the geographical region of Epirus.

OBJECTIVE

Our aim was to estimate the prevalence of the HLA-DRB1*1501, HLA-DQB1*0602 and HLA-DQA1*0102 alleles, consisting the most common susceptibility haplotype in North European and North American Caucasians.

METHODS

We studied 126 MS patients and 93 age and sex matched healthy controls. HLA typing was performed by a polymerase chain reaction (PCR) amplification with sequence-specific primers (PCR-SSP) method.

RESULTS

We found that HLA-DRB1*1501, HLA-DQB1*0602 and HLA-DQA1*0102 alleles were significantly more frequent among patients (34% versus 11%, p=0.00015; 69% versus 51%, p=0.01; 76% versus 55%, p=0.002, respectively). HLA-DRB1*1501, HLA-DQB1*0602, HLA-DQA1*0102 haplotype was significantly more common among patients (p=0.00067). HLA-DRB1*1501 and HLA-DQB1*0602 alleles were more frequently detected in patients with initial symptoms from the brainstem or the cerebellum (p=0.024). No significant correlation was observed among these alleles with sex, disease clinical course, or age at onset.

CONCLUSION

This is the first study to investigate genetic susceptibility to MS in Greece. Our results are in line with previous reports in North European and North American patients.

HLA-DRB1: genetic susceptibility and disability progression in a Spanish multiple sclerosis population

BACKGROUND AND OBJECTIVE

The association of HLA-DRB1*15 with susceptibility to multiple sclerosis (MS) has been consistently reported although its effect on the clinical phenotype is still controversial. The objectives of this study are to investigate the influence of the HLA-DRB1 alleles on the genetic susceptibility to MS and to study their impact on disability progression in a Spanish population.

METHODS

HLA-DRB1 typing was performed by PCR-SSP in 380 patients with sporadic MS and 1088 unrelated healthy controls. Allelic frequencies were compared between groups. We studied the correlation between the different alleles and the progression of MS.

RESULTS

The HLA-DRB1*15 allele in patients with MS had a statistically significant higher frequency when compared with controls (18.9% in patients vs. 10.1% in controls, Odds ratio (OR)=2.07, 95% CI=1.64-2.60, P<0.001). In the univariate analysis, the DRB1*01 and DRB1*04 alleles were associated with a worse prognosis when considering the time to reach an EDSS of 6, whereas the DRB1*03 was correlated with a better outcome. In the multivariate analysis, the alleles*01 and *04 were demonstrated to be independent factors to have a worse prognosis.

CONCLUSIONS

HLA-DRB1*15 is associated with MS when comparing patients with unrelated healthy controls in a Spanish population. The HLA-DRB1*01 and HLA-DRB1*04 alleles are related to a worse prognosis when considering the time taken to reach severe disability.

Relationship between HLA-DRB1 polymorphism and susceptibility or resistance to multiple sclerosis in Caucasians: a meta-analysis of non-family-based studies

OBJECTIVE

To identify the contribution of HLA-DRB1 alleles to susceptibility or resistance to multiple sclerosis (MS) in Caucasians through a meta-analysis of non-family-based studies.

METHODS

A systematic review of case-control studies in Caucasians was performed. Studies examining allele or phenotype frequencies were analyzed separately. Odds ratio (OR) and 95% confidence intervals (CIs) were used. We also used the relatively predispositional effect (RPE) method to analyze several allele frequency studies to avoid skewed results due to some strongly associated alleles.

RESULTS

A total of 5464 cases and 7809 controls from 14 allele frequency studies and a total of 5401 cases and 7538 controls from 23 phenotype frequency studies were analyzed. DRB1*15 was definitely the strongest risk factor for MS (allele group, Pc<0.00013, OR 2.59, 95%CI 2.34-2.87; phenotype group, Pc<0.00013, OR 3.35, 95%CI 2.95-3.80). DRB1*03 frequencies were significantly increased among MS cases in the phenotype group (Pc= 0.0013, OR 1.21, 95%CI 1.09-1.33) but not in the allele group. DRB1*14 and DRB1*07 showed protective effects against MS in both groups (DRB1*14, allele group, Pc<0.00013, OR 0.53, 95%CI 0.42-0.66; phenotype group, Pc<0.00013, OR 0.57, 95%CI 0.45-0.71; DRB1*07, allele group, Pc<0.0026, OR 0.75, 95%CI 0.64-0.87; phenotype group, Pc<0.00013, OR 0.67, 95%CI 0.61-0.73). By RPE method, DRB1*14, and DRB1*07 showed protective effects after excluding DRB1*15 from the analysis. DRB1*03 was significantly higher in MS cases than controls after removing both DRB1*15 and DRB1*14.

CONCLUSIONS

In Caucasians, we highlighted the definite protective role of HLA-DRB1*14 and DRB1*07 for MS. DRB1*03 is probably the only risk factor for MS besides DRB1*15 and a common genetic foundation for autoimmune disease. Targeting to these alleles may have potential values in prevention or therapy for MS in the specific population.

Heterogeneity at the HLA-DRB1 allelic variation locus does not influence multiple sclerosis disease severity, brain atrophy or cognition

BACKGROUND

HLA-DRB1*1501 (DR15) and other HLA class II alleles increase the risk of developing multiple sclerosis (MS). However, the contribution of genetic heterogeneity to the clinical course of MS remains controversial. We examined the influence of DR15 and other common DRB1 alleles (DRB1*01 (DR1), DRB1*03 (DR3) and DRB1*04 (DR4) on MS severity in a large, Australian, population-based cohort.

METHODS

We studied the association between common HLA-DRB1 alleles and genotypes and age of onset as well as three clinical disease severity descriptors: Multiple Sclerosis Severity Score, progression index), and the interval between the first and second attack in 978 patients with relapsing remitting MS and secondary progressive MS. We assessed cognition using the Symbol Digit Modalities Test in 811 patients and brain atrophy using the linear magnetic resonance imaging marker, the intercaudate ratio, in 745 patients.

RESULTS

Carrying DR15 significantly decreased the age of MS onset by 3.2 years in homozygotes and 1.3 years in heterozygotes. Carrying the HLA-DR15, -DR1, -DR3 or -DR4 alone or in combination did not affect clinical disease severity, cognition or cerebral atrophy.

CONCLUSIONS

This study confirms that heterogeneity of HLA-DRB1 does not influence disease outcome in relapsing MS patients, with the exception of a younger age of onset in HLA-DR15 carriers.

A polymorphism in the HLA-DPB1 gene is associated with susceptibility to multiple sclerosis

We conducted an association study across the human leukocyte antigen (HLA) complex to identify loci associated with multiple sclerosis (MS). Comparing 1927 SNPs in 1618 MS cases and 3413 controls of European ancestry, we identified seven SNPs that were independently associated with MS conditional on the others (each P ≤ 4 x 10(-6)). All associations were significant in an independent replication cohort of 2212 cases and 2251 controls (P ≤ 0.001) and were highly significant in the combined dataset (P ≤ 6 x 10(-8)). The associated SNPs included proxies for HLA-DRB1*15:01 and HLA-DRB1*03:01, and SNPs in moderate linkage disequilibrium (LD) with HLA-A*02:01, HLA-DRB1*04:01 and HLA-DRB1*13:03. We also found a strong association with rs9277535 in the class II gene HLA-DPB1 (discovery set P = 9 x 10(-9), replication set P = 7 x 10(-4), combined P = 2 x 10(-10)). HLA-DPB1 is located centromeric of the more commonly typed class II genes HLA-DRB1, -DQA1 and -DQB1. It is separated from these genes by a recombination hotspot, and the association is not affected by conditioning on genotypes at DRB1, DQA1 and DQB1. Hence rs9277535 represents an independent MS-susceptibility locus of genome-wide significance. It is correlated with the HLA-DPB1*03:01 allele, which has been implicated previously in MS in smaller studies. Further genotyping in large datasets is required to confirm and resolve this association.

Association of susceptibility to multiple sclerosis in Southern Han Chinese with HLA-DRB1, -DPB1 alleles and DRB1-DPB1 haplotypes: distinct from other populations

Association of HLA class II with multiple sclerosis (MS) has been widely studied in both Western and Oriental populations. However, such an association is not well documented in Chinese. The objective of this study was to examine the association between the susceptibility to conventional MS in Southern Chinese with HLA-DRB1,-DPB1 alleles and putative DRB1-DPB1 haplotypes. Genotyping of HLA-DRB1 and -DPB1 alleles was performed in 60 patients with conventional MS and 95 controls. Allele frequencies were compared between patients and controls to identify MSassociated alleles. Relative predisposing effect method was used to compare haplotype frequencies in patients and controls and to identify possible predisposing DRB1-DPB1 haplotypes, which were further examined for differences in haplotype carriage rates between the two groups. We found that the allele frequency of DRB1*1501 was not different between patients (18.3%) and controls (21.1%) ( p = 0.837). In contrast, frequency of the DPB1*0501 allele was significantly higher in patients (90%) than in controls (67.4%) (odds ratio = 4.36, p = 0.0013, pcorr = 0.025). DRB1-DPB1 linkage haplotype in patients (8.33%) was significantly higher than in controls (0%) ( p < 0.0001) and the carriage rate of this haplotype was significantly increased in patients (15%) as compared with controls (0%) ( p = 0.00013, pcorr = 0.003). Combined, these results suggest that HLA-DRB1*1501 is not associated with susceptibility to conventional MS in Southern Chinese. Instead, both the DPB1*0501 allele and the DRB1*1602- DPB1*0501 haplotype are strong predisposing factors for conventional MS in this population. Our results establish that the HLA profiles of MS in Southern Chinese are distinct from other populations.

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.

The genetics of multiple sclerosis: SNPs to pathways to pathogenesis

Multiple sclerosis (MS) is an autoimmune demyelinating disease and a common cause of neurological disability in young adults. The modest heritability of MS reflects complex genetic effects and multifaceted gene-environment interactions. The human leukocyte antigen (HLA) region is the strongest susceptibility locus for MS, but a genome-wide association study recently identified new susceptibility genes. Progress in high-throughput genotyping and sequencing technologies and a better understanding of the structural organization of the human genome, together with powerful brain-imaging techniques that refine the phenotype, suggest that the tools could finally exist to identify the full set of genes influencing the pathogenesis of MS.

The immunogenetics of multiple sclerosis

The discoveries in the 1970s of strong associations between various diseases and certain human leukocyte antigen (HLA) factors were a revolution within genetic epidemiology in the last century by demonstrating for the first time how genetic markers can help unravel the genetics of disorders with complex genetic backgrounds. HLA controls immune response genes and HLA associations indicate the involvement of autoimmunity. Multiple sclerosis (MS) was one of the first conditions proven to be HLA associated involving primarily HLA class II factors. We review how HLA studies give fundamental information on the genetics of the susceptibility to MS, on the importance of linkage disequilibrium in association studies, and on the pathogenesis of MS. The HLA-DRB1*1501 molecule may explain about 50% of MS cases and its role in the pathogenesis is supported by studies of transgenic mice. Studies of polymorphic non-HLA genetic markers are discussed based on linkage studies and candidate gene approaches including complete genome scans. No other markers have so far rivaled the importance of HLA in the genetic susceptibility to MS. Recently, large international collaborations provided strong evidence for the involvement of polymorphism of two cytokine receptor genes in the pathogenesis of MS: the interleukin 7 receptor alpha chain gene (IL7RA) on chromosome 5p13 and the interleukin 2 receptor alpha chain gene (IL2RA (=CD25)) on chromosome 10p15. It is estimated that the C allele of a single nucleotide polymorphism, rs6897932, within the alternative spliced exon 6 of IL7RA is involved in about 30% of MS cases.

An extremes of outcome strategy provides evidence that multiple sclerosis severity is determined by alleles at the HLA-DRB1 locus

Multiple sclerosis (MS) is a common inflammatory disease of the central nervous system unsurpassed for variability in disease outcome. A cohort of sporadic MS cases (n = 163), taken from opposite extremes of the distribution of long-term outcome, was used to determine the role of the HLA-DRB1 locus on MS disease severity. Genotyping sets of benign and malignant MS patients showed that HLA-DRB1*01 was significantly underrepresented in malignant compared with benign cases. This allele appears to attenuate the progressive disability that characterizes MS in the long term. The observation was doubly replicated in (i) Sardinian benign and malignant patients and (ii) a cohort of affected sibling pairs discordant for HLA-DRB1*01. Among the latter, mean disability progression indices were significantly lower in those carrying the HLA-DRB1*01 allele compared with their disease-concordant siblings who did not. The findings were additionally supported by similar transmission distortion of HLA-DRB1*04 subtypes closely related to HLA-DRB1*01. The protective effect of HLA-DRB1*01 in sibling pairs may result from a specific epistatic interaction with the susceptibility allele HLA-DRB1*1501. A high-density (>700) SNP examination of the MHC region in the benign and malignant patients could not identify variants differing significantly between the two groups, suggesting that HLA-DRB1 may itself be the disease-modifying locus. We conclude that HLA-DRB1*01, previously implicated in disease resistance, acts as an independent modifier of disease progression. These results closely link susceptibility to long-term outcome in MS, suggesting that shared quantitative MHC-based mechanisms are common to both, emphasizing the central role of this region in pathogenesis.

Primary-progressive multiple sclerosis

About 10-15% of patients with multiple sclerosis (MS) present with gradually increasing neurological disability, a disorder known as primary-progressive multiple sclerosis (PPMS). Compared with relapse-onset multiple sclerosis, people with PPMS are older at onset and a higher proportion are men. Inflammatory white-matter lesions are less evident but diffuse axonal loss and microglial activation are seen in healthy-looking white matter, in addition to cortical demyelination, and quantitative MRI shows atrophy and intrinsic abnormalities in the grey matter and the white matter. Spinal cord atrophy corresponds to the usual clinical presentation of progressive spastic paraplegia. Although neuroaxonal degeneration seems to underlie PPMS, the pathogenesis and the extent to which immune-mediated mechanisms operate is unclear. MRI of the brain and spinal cord, and examination of the CSF, are important investigations for diagnosis; conventional immunomodulatory therapies, such as interferon beta and glatiramer acetate, are ineffective. Future research should focus on the clarification of the mechanisms of axonal loss, improvements to the design of clinical trials, and the development of effective neuroprotective treatments.

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.

The role of HLA-DRB1 alleles on susceptibility and outcome of a Portuguese Multiple Sclerosis population

BACKGROUND

The association between susceptibility to multiple sclerosis (MS) and HLA-DRB1*15 has been reported in various European populations.

OBJECTIVE

To investigate the relationship between MS, HLA-DRB1*15 and other DRB1 alleles in a Portuguese population and their association with clinical course of MS.

METHODS

The HLA-DRB1 alleles were analyzed by PCR-SSP in 248 MS patients and 282 healthy controls. In order to relate HLA-DRB1 alleles to disease aggressiveness, patients with relapsing remitting MS and secondary progressive MS were subdivided into 3 groups: 'benign' MS patients who maintain an Extended Disability Status Scale (EDSS) score of <or=3 at least 10 years after disease onset; non-benign MS patients with EDSS>3 after the same period and 'aggressive' MS those with EDSS>or=6 within 15 years of disease onset.

RESULTS

As expected, a higher frequency of HLA-DRB1*15 was found in MS patients (29.8% vs 19.9%, odds ratio (OR)=1.72, 95% CI=1.15-2.56, p=0.008). The HLA-DRB1*03 allele was positively associated with MS in the overall patient population (22.6% vs 15.6%, OR=1.58, 95% CI=1.02-2.45). Concerning disease aggressiveness, HLA-DRB1*15 occurred more frequently in the group with benign disease (42.6% vs 19.9%, OR=2.99, 95% CI=1.56-5.72) and in the group with non-benign disease (34.1% vs 19.9%, OR=2.09, 95% CI=1.05-4.16) compared with controls. When time to reach an EDSS=3 or EDSS=6 was considered as end point, HLA-DRB1*15 negative patients were found to have a worse prognosis.

CONCLUSIONS

In this population of Portuguese MS patients, the HLA-DRB1*15 allele is established as a genetic marker for susceptibility to MS and is also associated with a better outcome.

Interferon-beta1b treatment modulates cytokines in patients with primary progressive multiple sclerosis

OBJECTIVES

It is unknown whether the immunological effects of beta-interferon (IFN-beta) differ in primary progressive multiple sclerosis (PPMS) when compared with relapsing-remitting multiple sclerosis (RRMS). Therefore, we investigated the effects of IFN-beta1b treatment in PPMS on proliferation and cytokine pattern of peripheral blood mononuclear cells (PBMC) and interleukin-10 (IL-10) serum level.

METHODS

Eighteen patients were treated with IFN-beta1b for 12 months in an open-label trial. Serum and PBMC were collected longitudinally.

RESULTS

Interleukin-10 serum levels increased (P = 0.02) during treatment. Tumor necrosis factor-alpha was increased in anti CD3 (OKT3) antibody stimulated PBMC during treatment (P = 0.04), whereas secretion of IL-10 was decreased in OKT3 (P = 0.04), but increased in concavalin A stimulated PBMC (P = 0.02).

CONCLUSIONS

Interleukin-10 serum levels rose in IFN-beta1b-treated patients as has been observed in RRMS. The changes in cytokine patterns secreted by T-lymphocytes of PPMS patients, however, differ from effects observed in RRMS supporting the hypothesis that PPMS differs in some immunological aspects from RRMS.

Human leucocyte antigen class II polymorphism in Irish patients with multiple sclerosis

The contribution of human leucocyte antigen (HLA) to the genetic risk for multiple sclerosis (MS) in patients of Northern European Caucasoid ancestry has been known since the 1970s. The northern part of Ireland, including county Donegal, is known to be a high-risk area for the development of MS. Recorded prevalence rates for county Wexford in the south-east Ireland have been markedly lower and suggest the existence of a prevalence gradient within the island. To evaluate the association of HLA-DRB1 and -DQB1 haplotypes with MS in both Wexford and Donegal, we examined a total of 118 patients and 400 regionally matched controls. The aim of this exploratory study was to test the possibility of heterogeneity in HLA class II associations with MS and to identify potential predisposing or protective haplotypes, associated with MS risk in Ireland. We confirmed the association of DRB1*1501-DQB1*0602 haplotype carriage with MS in both Wexford [odds ratio (OR) = 2.95, P= 0.0020, P(cor)= 0.0220] and Donegal (OR = 2.29, P= 0.0030, P(cor)= 0.0420). A higher frequency and a significantly higher homozygosity rate of this haplotype in Donegal are likely contributing factors to the higher prevalence of MS in Donegal compared with Wexford. The distribution of HLA class II alleles among Irish MS patients and controls establishes that there is heterogeneity in HLA class II associations with MS within Ireland.

Heterogeneity at the HLA-DRB1 locus and risk for multiple sclerosis

Variation in major histocompatibility complex genes on chromosome 6p21.3, specifically the human leukocyte antigen HLA-DR2 or DRB1*1501-DQB1*0602 extended haplotype, confers risk for multiple sclerosis (MS). Previous studies of DRB1 variation and both MS susceptibility and phenotypic expression have lacked statistical power to detect modest genotypic influences, and have demonstrated conflicting results. Results derived from analyses of 1339 MS families indicate DRB1 variation influences MS susceptibility in a complex manner. DRB1*15 was strongly associated in families (P=7.8x10(-31)), and a dominant DRB1*15 dose effect was confirmed (OR=7.5, 95% CI=4.4-13.0, P<0.0001). A modest dose effect was also detected for DRB1*03; however, in contrast to DRB1*15, this risk was recessive (OR=1.8, 95% CI=1.1-2.9, P=0.03). Strong evidence for under-transmission of DRB1*14 (P=5.7x10(-6)) even after accounting for DRB1*15 (P=0.03) was present, confirming a protective effect. In addition, a high risk DRB1*15 genotype bearing DRB1*08 was identified (OR=7.7, 95% CI=4.1-14.4, P<0.0001), providing additional evidence for trans DRB1 allelic interactions in MS. Further, a significant DRB1*15 association observed in primary progressive MS families (P=0.0004), similar to relapsing-remitting MS families, suggests that DRB1-related mechanisms are contributing to both phenotypes. In contrast, results obtained from 2201 MS cases argue convincingly that DRB1*15 genotypes do not modulate age of onset, or significantly influence disease severity measured using expanded disease disability score and disease duration. These results contribute substantially to our understanding of the DRB1 locus and MS, and underscore the importance of using large sample sizes to detect modest genetic effects, particularly in studies of genotype-phenotype relationships.

Intravenous synthetic peptide MBP8298 delayed disease progression in an HLA Class II-defined cohort of patients with progressive multiple sclerosis: results of a 24-month double-blind placebo-controlled clinical trial and 5 years of follow-up treatment

MBP8298 is a synthetic peptide with a sequence corresponding to amino acid residues 82-98 of human myelin basic protein (DENPVVHFFKNIVTPRT). It represents the immunodominant target for both B cells and T cells in multiple sclerosis (MS) patients with HLA haplotype DR2. Its administration in accordance with the principle of high dose tolerance results in long-term suppression of anti-myelin basic protein (MBP) autoantibody levels in the cerebrospinal fluid (CSF) of a large fraction of progressive MS patients. MBP8298 was evaluated in a 24-month placebo-controlled double-blinded Phase II clinical trial in 32 patients with progressive MS. The objective was to assess the clinical efficacy of 500 mg of MBP8298 administered intravenously every 6 months, as measured by changes in Expanded Disability Status Scale (EDSS) scores. Contingency analysis for all patients at 24 months showed no significant difference between MBP8298 and placebo-treatments (n = 32, P = 0.29). Contingency analysis in an HLA Class II defined subgroup showed a statistically significant benefit of MBP8298 treatment compared with placebo in patients with HLA haplotypes DR2 and/or DR4 (n = 20, P = 0.01). Long-term follow-up treatment and assessment of patients in this responder group showed a median time to progression of 78 months for MBP8298 treated patients compared with 18 months for placebo-treatment (Kaplan-Meier analysis, P = 0.004; relative rate of progression = 0.23). Anti-MBP autoantibody levels in the CSF of most MBP8298 treated patients were suppressed, but antibody suppression was not predictive of clinical benefit. Anti-MBP autoantibodies that reappeared in the CSF of one patient at 36 months, whilst under treatment with MBP8298, were not reactive with the MBP8298 peptide in vitro. The identification of a responder subgroup (62.5% of the patients in this study) enables a more efficient design of a large confirmatory clinical trial of MBP8298. The probability that patients with other less common HLA-DR haplotypes will respond to this treatment should not be ignored.

Benign course in multiple sclerosis: a review

Since the 1950s, it has been recognized that a subgroup of multiple sclerosis (MS) patients exists that shows little or no progression in the severity of the disease over time. This group is referred to as 'benign' MS. Although a substantial amount of research in MS indicates a multifactorial background in disease severity, to date it is still difficult to predict whether the course will be benign at onset and it is difficult to find factors that influence the course of the disease over time. Maintaining or restoring neural conduction inside a central nervous system lesion seems to be the essence of staying 'benign'.

Multiple sclerosis genetics: leaving no stone unturned

Compelling epidemiologic and molecular data indicate that genes play a primary role in determining who is at risk for developing multiple sclerosis (MS), how the disease progresses, and how someone responds to therapy. The genetic component of MS etiology is believed to result from the action of allelic variants in several genes. Their incomplete penetrance and moderate individual effect probably reflects epistatic interactions, post-transcriptional regulatory mechanisms, and significant environmental influences. Equally significant, it is also likely that locus heterogeneity exists, whereby specific genes influence susceptibility and pathogenesis in some individuals but not in others. With the aid of novel analytical algorithms, the combined study of genomic, transcriptional, proteomic, and phenotypic information in well-controlled study groups will define a useful conceptual model of pathogenesis and a framework for understanding the mechanisms of action of existing therapies for this disorder, as well as the rationale for novel curative strategies.

Population frequency of HLA haplotypes contributes to the prevalence difference of multiple sclerosis in Ireland

BACKGROUND

A recent epidemiological study of multiple sclerosis in County Donegal in the northwest of Ireland and County Wexford in the southeast found a significant prevalence difference of 63.9/100,000 (95% CI 49.3-82.7/100,000) between the two regions (Z = 3.94, p <or= 0.001). County Donegal had a higher prevalence rate than County Wexford (184.6/100,000 vs. 120.7/ 100,000). The aim of this paper is to examine whether the MS prevalence difference between the two counties is due to population differences in the genetic predisposition to MS.

METHODS

Seventy-three MS patients from County Donegal and 45 from County Wexford participated in the study and 200 control subjects were enrolled from each county. Blood samples from both MS populations and control populations were HLA typed for DRB1 and DQB1 alleles.

RESULTS

The strong association with the development of MS and the HLA DRB1*1501 and DQB1*0602 phenotypes was confirmed in both patient populations relative to controls. The Donegal sample control population also had a significantly higher carriage rate of the HLA DRB1*1501 - DQB1*0602 haplotype relative to the Wexford sample control population (chi(2) = 5.02, p <or= 0.05,OR = 1.616, CI 1.060-2.464, p = 0.05).

CONCLUSION

Although the numbers tested in this study were small the results suggest one of the factors accounting for the difference in MS prevalence across the island of Ireland is likely to be variation in the genetic predisposition to MS within the Irish population.

The presence of glutamic acid at positions 71 or 74 in pocket 4 of the HLA-DRbeta1 chain is associated with the clinical course of multiple sclerosis

BACKGROUND

Primary progressive multiple sclerosis (PP-MS) differs from relapsing-remitting or secondary progressive MS (RR/SP-MS) in ways suggesting differences in the pathogenic pathways. Susceptibility to both PP-MS and RR/SP-MS is linked to carriage of the HLA molecule DRB1*1501. Several serologically defined HLA-DR groups (DR1, DR4, DR6, and DR9) occur less often in RR/SP-MS than in controls. Some or all of the HLA-DR molecules encoded by alleles in these serologically defined groups have a negatively charged glutamic acid at residue 71 or 74 of the beta1 chain (beta1(71)/beta1(74)). Residues at these positions are important in the formation of pocket 4 in the antigen binding site of the HLA-DR molecule.

OBJECTIVES

To investigate whether the presence of alleles encoding HLA-DR molecules containing glutamic acid at beta1(71)/beta1(74) correlates with the course of MS.

METHODS

HLA-DR and HLA-DQ alleles and genotypes were analysed in 121 MS patients (50 with PP-MS) and 109 controls by molecular typing.

RESULTS

Alleles encoding HLA-DR molecules containing a glutamic acid at beta1(71)/beta1(74) occurred less often in patients with RR/SP-MS than in those with PP-MS or controls. In subjects not carrying the DRB1*1501 allele, a much higher proportion of PP-MS patients carried alleles encoding HLA-DR molecules containing a glutamic acid at beta1(71)/beta1(74) than did RR/SP-MS patients or controls.

CONCLUSIONS

The amino acid residues involved in determining the shape and charge of pocket 4 of the HLA-DR beta1 chain could influence the clinical course of MS by determining protection against RR/SP-MS or susceptibility to the development of PP-MS.

Influence of CCR5 delta32 polymorphism on multiple sclerosis susceptibility and disease course

The CCR5 chemokine receptor has been implicated in the pathogenesis of multiple sclerosis (MS). We carried out an allelic association study using a deletion polymorphism in the coding region of the CCR5 gene in 331 relapsing-remitting (RR) and secondary progressive (SP) MS patients, 108 primary progressive (PP) MS patients and 230 healthy controls. Of the 331 RR and SPMS patients, 172 were recruited from specialist clinics and 159 from a population survey. Disease severity was assessed clinically using the Expanded Disability Status Scale (EDSS) and used to calculate a progression index for each patient (defined as EDSS divided by duration of disease). No significant difference in distribution of the CCR5 delta32 allele was observed between the 331 RR/SPMS patients and controls, between the 108 PPMS patients and controls or between the PPMS and RR/SPMS groups. Furthermore, no differences in rate of disease progression were detected between carriers and noncarriers of the delta32 allele. In the population-based group of RR/SPMS patients, carriage of the CCR5 delta32 polymorphism was associated with a lower age at disease onset (mean age 26.562 versus 31.065 years, P = 0.003). However, no significant differences in age of onset were present in the PPMS group or in a second RRMS population. These results suggest that the CCR5 delta32 polymorphism is not a major determinant of susceptibility to develop MS in the population under study, and conflict with a previously reported association between CCR5 delta32 carriage and a better prognosis.

A genome wide scan for association with multiple sclerosis in a N. Irish case control population

In order to screen the genome for linkage disequilibrium (LD) in multiple sclerosis (MS), we typed 2537 microsatellite markers in separately pooled DNA from 200 cases and 200 controls from N. Ireland. Twenty two markers showing significant evidence of association were identified including three from the HLA region on chromosome 6p21. Putative candidate genes mapping close to the 19 novel markers include the IL10RA and CD3E genes on 11q23 (which both lie close to the marker D11S1998). Individual typing of the marker D11S1998 confirmed its association.

Genetics of multiple sclerosis: linkage and association studies

Multiple sclerosis (MS) is a demyelinating autoimmune disease of the central nervous system caused by an interplay of environmental and genetic factors. The only genetic region that has been clearly demonstrated by linkage and association studies to contribute to MS genetic susceptibility is the human leukocyte antigen (HLA) system. The majority of HLA population studies in MS have focused on Caucasians of Northern European descent, where the predisposition to disease has been consistently associated with the class II DRB1*1501-DQA1*0102-DQB1*0602 haplotype. A positive association with DR4 was detected in Sardinians and in other Mediterranean populations. Moreover DR1, DR7, DR11 have been found to be protective in several populations. Systematic searches aimed at identifying non-HLA susceptibility genes were undertaken in several populations by means of linkage studies with microsatellite markers distributed across the whole genome. The conclusion of these studies was that there is no major MS locus, and genetic susceptibility to the disease is most likely explained by the presence of different genes each conferring a small contribution to the overall familial aggregation. The involvement of several candidate genes was tested by association studies, utilizing either a population-based (case control) or a family-based (transmission disequilibrium test) approach. Candidate genes were selected mainly on the basis of their involvement in the autoimmune pathogenesis and include immunorelevant molecules such as cytokines, cytokine receptors, immunoglobulin, T cell receptor subunits and myelin antigens. With the notable exception of HLA, association studies met only modest success. This failure may result from the small size of the tested samples and the small number of markers considered for each gene. New tools for large scale screening are needed to identify genetic determinants with a low phenotypic effect. Large collaborative studies are planned to screen several thousands of patients with MS with several thousands of genetic markers. The tests are increasingly based on the DNA pooling procedure.

Primary progressive multiple sclerosis: increasing clarity but many unanswered questions

Heterogeneity in the clinical course of multiple sclerosis (MS) is well recognised and patients following a primary progressive course, 10-15% of the MS population, have a distinct clinical and paraclinical phenotype. This review examines recent advances in our understanding of this subgroup of patients and examines the new criteria to be applied in diagnosis. It also highlights developments in genetic, immunological, magnetic resonance and pathological aspects of the disease, whilst also outlining the results of recent therapeutic trials.

Genetic dissection of the human leukocyte antigen region by use of haplotypes of Tasmanians with multiple sclerosis

Association of multiple sclerosis (MS) with the human leukocyte antigen (HLA) class II haplotype DRB1*1501-DQB1*0602 is the most consistently replicated finding of genetic studies of the disease. However, the high level of linkage disequilibrium (LD) in the HLA region has hindered the identification of other loci that single-marker tests for association are unlikely to resolve. In order to address this issue, we generated haplotypes spanning 14.754 Mb (5 cM) across the entire HLA region. The haplotypes, which were inferred by genotyping relatives of 152 patients with MS and 105 unaffected control subjects of Tasmanian ancestry, define a genomic segment from D6S276 to D6S291, including 13 microsatellite markers integrated with allele-typing data for DRB1 and DQB1. Association to the DRB1*1501-DQB1*0602 haplotype was replicated. In addition, we found that the class I/extended class I region, defined by a genomic segment of approximately 400 kb between MOGCA and D6S265, harbors genes that independently increase risk of, or provide protection from, MS. Log-linear modeling analysis of constituent haplotypes that represent genomic regions containing class I (MOGCA-D6S265), class III (TNFa-TNFd-D6S273), and class II (DRB1-DQB1) genes indicated that having class I and class II susceptibility variants on the same haplotype provides an additive effect on risk. Moreover, we found no evidence for a disease locus in the class III region defined by a 150-kb genomic segment containing the TNF locus and 14 other genes. A global overview of LD performed using GOLD identified two discrete blocks of LD in the HLA region that correspond well with previous findings. We propose that the analysis of haplotypes, by use of the types of approaches outlined in the present article, should make it possible to more accurately define the contribution of the HLA to MS.

Identifying disease modifying genes in multiple sclerosis

Evidence is mounting that genetic variation influences not only susceptibility to multiple sclerosis (MS), but also its course and severity. Identification of disease modifying genes, however, poses unique challenges, especially on how to classify the course and outcome of the disease in ways that may be relevant to analysis of biological factors that might be influenced by genes. The power of the statistical approaches to detect small effects of individual genes in complex disorders such as MS is problematic, and approaches to estimate power must be appropriate for the data. Nonetheless, using contemporary schemes of classification, genetic variants that influence disease course have been found; in fact, a small number have been confirmed to influence disease course in two or more independent studies. This review addresses strategies relevant to identification of disease modifying genes in MS, and summarizes and critically evaluates the current state of knowledge in this area.

HLA-DR 15 is associated with female sex and younger age at diagnosis in multiple sclerosis

BACKGROUND

The association between multiple sclerosis and class II alleles of the major histocompatibility complex, in particular the DRB1*1501-DQB1*0602 haplotype, is well established but their role in determining specific features of this clinically heterogeneous disease is unknown as few studies involving large sample sizes have been performed.

METHODS

729 patients with multiple sclerosis were typed for the HLA DR15 phenotype. All patients underwent clinical assessment and a detailed evaluation of their clinical records was undertaken.

RESULTS

The presence of DR15 was associated with younger age at diagnosis and female sex but there was no association with disease course (relapsing-remitting or secondary progressive v primary progressive type), disease outcome, specific clinical features (opticospinal v disseminated form), diagnostic certainty (clinically and laboratory supported definite v clinically probable multiple sclerosis), and paraclinical investigations including the presence of oligoclonal bands in the CSF or characteristic abnormalities on MRI imaging of the central nervous system.

CONCLUSION

Even though DR15 carriers are more likely to be female and prone to an earlier disease onset, the results indicate that there is no association with other specific clinical outcomes or laboratory indices examined here. This suggests that DR15 exerts a susceptibility rather than disease modifying effect in multiple sclerosis.

Genetic basis for clinical expression in multiple sclerosis

Multiple sclerosis is a clinically heterogeneous demyelinating disease and an important cause of acquired neurological disability. An underlying complex genetic susceptibility plays an important role in multiple sclerosis aetiology; however, the role of genetic factors in determining clinical features of multiple sclerosis is unknown. We studied 184 stringently ascertained Caucasian multiple sclerosis families with multiple affected cases. A detailed evaluation of patient histories identified clinical variables including age of onset, initial clinical manifestations and disease severity. The concordance within families for continuous and categorical clinical variables was investigated using an intraclass correlation or Cohen's kappa coefficient, respectively. Genetic analyses included model-dependent, model-independent and association methodology. Linear and logistic regression models were used to evaluate the effect of human leucocyte antigen (HLA)-DR2 (DRB1*1501, DQB1*0602) on clinical outcome, taking account of correlation within families. Significant concordance for early clinical manifestations within families was observed for individuals with exclusive optic neuritis and/or spinal cord involvement as first and second multiple sclerosis attacks (P < 10(-6)). Linkage (LOD = 3.80, theta = 0.20) and association (P = 0.0002) to HLA-DR were present in the dataset; however, linkage was restricted to families in which the DR2 haplotype was present in at least one nuclear member. No evidence for linkage to HLA-DR in DR2-negative families was observed. When families were stratified by concordance of early clinical manifestations, a significant DR2 association was present in all subgroups. Concordance for early manifestations of multiple sclerosis was present in this familial dataset, but was not associated with HLA-DR2. The association of DR2 in families with different clinical presentations suggests that a common basis exists for susceptibility in multiple sclerosis. However, non-HLA genes or other epigenetic factors must modulate disease expression. Locus heterogeneity at the HLA region suggests a distinct immunopathogenesis in DR2 negative patients.

Additive effect of the HLA-DR15 haplotype on susceptibility to multiple sclerosis

Multiple sclerosis (MS) has been associated with the human leukocyte antigen DR15 allele in Caucasians of North and Central European origin. However, the relative effect of the DR15 homozygous and the DR15 heterozygous genotypes on the disease susceptibility is unclear. Based upon results from three North European studies we have examined this by meta-analysis. Our results suggested that the effect of the DRB1*1501,DQA1*0102,DQB1*0602 haplotype on the susceptibility to MS is additive, perhaps reflecting that development of the disease is facilitated by a high density surface expression of the antigen presenting molecules encoded by this haplotype. Possible implications of our finding to future studies of the genetic background of MS is discussed.

Polymorphism and distribution of HLA-DR2 alleles in Mexican populations

DRB1*15/16 nucleotide polymorphism was analyzed in 68 DR2 positive individuals (18 Mexican Mestizos, 30 Mazatecans and 20 Nahuas), carrying a total of 75 DR2 haplotypes. HLA-DR2 was one of the most frequent specificities detected in Mazatecans and Nahuas with gene frequency (gf) of 0.232 and 0.141, respectively. In these populations DRB1*16 was the most frequent DR2 split (gf = 0.183 in Mazatecans and gf = 0.135 in Nahuas), whereas in Mexican Mestizos the most frequent was DRB1*15 (gf = 0.065). Four DRB1-DQB1 combinations in Mexican Mestizos, two in Mazatecans and one in Nahuas were in linkage disequilibrium. In spite of the restricted polymorphism, there were differences on DRB1*15/16 alleles found in Mexicans. DRB1*1501 a Caucasian allele was predominant in Mexican Mestizos, whereas DRB1*1602 an Amerindian allele was characteristic on Indian populations. An important difference was detected among the Amerindian populations studied since DRB1*1502 was only present in Mazatecans. This data corroborates the restricted polymorphism of DRB1*15/16 and the high frequency of DRB1*16 subtype in autochthonous American populations and suggest that the differences in gene frequencies of DRB1*15/16 alleles could be helpful in distinguishing each of these population.

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.