Updated results of the United Kingdom linkage-based genome screen in multiple sclerosis

Multiple sclerosis genetics

Familial aggregation and the studies of twins indicate that heredity contributes to multiple sclerosis (MS) risk. Immunologic studies of leukocyte antigens subsequently followed by gene-mapping techniques identified the primary MS susceptibility locus to be within the major histocompatibility complex (MHC). The primary risk allele is HLA-DRB1*15, although other alleles of this gene also influence MS susceptibility. Other genes within the MHC also contribute to MS susceptibility. Genome-wide association studies have identified over 50 additional common variants of genes across the genome. Estimates suggest that there may be as many as 200 genes involved in MS susceptibility. In addition to these common polymorphisms, studies have identified several rare risk alleles in some families. Interestingly, the majority of the genes identified have known immunologic functions and many contribute to the risk of inheriting other autoimmune diseases. Genetic variants in the vitamin D metabolic pathway have also been identified. That vitamin D contributes to MS susceptibility as both an environmental as well as genetic risk factor underscores the importance of this metabolic pathway in disease pathogenesis. Current efforts are focused on understanding how the myriad of genetic risk alleles interact within networks to influence MS risk at family level as well as within populations.

The genetic aspects of multiple sclerosis

The epidemiology of multiple sclerosis has been extensively investigated and two features have consistently emerged: marked geographical variation in prevalence and substantial familial clustering. At first sight, geographic variation would seem to imply an environmental cause for the disease, while familial clustering would seem to suggest that genetic factors have the predominant etiological effect. However, given that geographic variation in prevalence could result from variation in the frequency of genetic risk alleles and that familial clustering might result from shared environmental exposure rather than shared genetic risk alleles, it is clear that these crude inferences are unreliable. Epidemiologists have been resourceful in their attempts to resolve this apparent conflict between “nurture and nature” and have employed a whole variety of sophisticated methods to try and untangle the etiology of multiple sclerosis. The body of evidence that has emerged from these efforts has formed the foundation for decades of research seeking to identify relevant genes and this is the obvious place to start any consideration of the genetics of multiple sclerosis.

Follow-up examination of linkage and association to chromosome 1q43 in multiple sclerosis

Multiple sclerosis is a debilitating neuroimmunological and neurodegenerative disease affecting more than 400,000 individuals in the United States. Population and family-based studies have suggested that there is a strong genetic component. Numerous genomic linkage screens have identified regions of interest for MS loci. Our own second-generation genome-wide linkage study identified a handful of non-MHC regions with suggestive linkage. Several of these regions were further examined using single-nucleotide polymorphisms (SNPs) with average spacing between SNPs of approximately 1.0 Mb in a dataset of 173 multiplex families. The results of that study provided further evidence for the involvement of the chromosome 1q43 region. This region is of particular interest given linkage evidence in studies of other autoimmune and inflammatory diseases including rheumatoid arthritis and systemic lupus erythematosus. In this follow-up study, we saturated the region with ~700 SNPs (average spacing of 10kb per SNP) in search of disease associated variation within this region. We found preliminary evidence to suggest that common variation within the RGS7 locus may be involved in disease susceptibility.

The complex genetics of multiple sclerosis: pitfalls and prospects

The genetics of complex disease is entering a new and exciting era. The exponentially growing knowledge and technological capabilities emerging from the human genome project have finally reached the point where relevant genes can be readily and affordably identified. As a result, the last 12 months has seen a virtual explosion in new knowledge with reports of unequivocal association to relevant genes appearing almost weekly. The impact of these new discoveries in Neuroscience is incalculable at this stage but potentially revolutionary. In this review, an attempt is made to illuminate some of the mysteries surrounding complex genetics. Although focused almost exclusively on multiple sclerosis all the points made are essentially generic and apply equally well, with relatively minor addendums, to any other complex trait, neurological or otherwise.

Linkage disequilibrium analyses within chromosome 19p in multiple sclerosis

OBJECTIVE

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

RESULTS

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

CONCLUSIONS

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

Multiple sclerosis genetics

Multiple sclerosis (MS) clusters with the so-called complex genetic diseases, a group of common disorders characterized by modest disease risk heritability and multifaceted gene-environment interactions. The major histocompatibility complex (MHC) is the only genomic region consistently associated with MS, and susceptible MHC haplotypes have been identified. Although the MHC does not account for all genetic contribution to MS, the other genetic contributors have been elusive. Microarray gene-expression studies, which also have not identified a major MS locus, have, however, been promising in elucidating some of the possible pathways involved in the disease. Yet, microarray studies thus far have been unable to separate the genetic causes of MS from the expression consequences of MS. The use of new methodologies and technologies to refine the phenotype, such as brain spectroscopy, PET and functional magnetic resonance imaging combined with novel computational tools and a better understanding of the human genome architecture, may help resolve the genetic causes of MS.

Multiple sclerosis susceptibility and the X chromosome

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

Recent advances in genetic analysis of multiple sclerosis: genetic associations and therapeutic implications

Epidemiological studies have confirmed that genetic factors are a key component in the pathogenesis of multiple sclerosis (MS) and that those determining MS susceptibility have been extensively studied. Many papers have been published regarding the heritable differences useful in genetic studies; these include variations in DNA, such as single-nucleotide polymorphisms, microsatellites and insertion/deletion polymorphisms. However, to date, among other regions, HLA is the only region confirmed to possess genes that determine MS susceptibility. In this article, we review the progress during the last 5 years in the studies on the susceptibility genes and the pharmacogenetics of MS. Newer techniques and methods of analysis will hopefully result in better screening of individuals who are at highest risk and novel treatments.

A follow-up study of Nordic multiple sclerosis candidate gene regions

In this study, the results from three Nordic linkage disequilibrium screens in multiple sclerosis (MS) were investigated, in a new sample set of 314 Nordic MS trios from Denmark, Norway, Sweden and Iceland. Among 30 non-HLA and two HLA microsatellite markers individually genotyped, eight markers displayed distorted transmission with uncorrected P-value <0.05, ranked in this order: D6S2443 (6p21.32, HLA class II) (P corrected =0.01), D2S2201 (2p24), D19S552 (19q13), D3S3584 (3q21), D17S975 (17q11), D1S2627 (1p22), D6S273 (6p21.33, HLA class III) and D12S1051 (12q23). These non-HLA regions need further investigation as possible MS candidate gene regions in our population. Multiple Sclerosis 2007; 13: 584-589. http://msj.sagepub.com

Meta-analysis of genome-wide linkage studies for multiple sclerosis, using an extended GSMA method

Many genome-wide linkage studies in multiple sclerosis (MS) have been performed, but results are disappointing, with linkage confirmed only in the HLA region. We combined results from all available, non-overlapping genome-wide linkage studies in MS using the Genome Search Meta-Analysis method (GSMA). The GSMA is a rank-based analysis, which assesses the strongest evidence for linkage within bins of traditionally 30 cM width on the autosomes and X chromosome. Genome-wide evidence for linkage was confirmed on chromosome 6p (HLA region; P=0.00004). Suggestive evidence for linkage was found on chromosomes 10q (P=0.0077), 18p (P=0.0054) and 20p (P=0.0079). To explore how these results could be affected by bin definition, we analysed the data using different bin widths (20 and 40 cM) and using a shifted 30 cM bin by moving bin boundaries by 15 cM. Consistently significant results were obtained for the 6p region. The regions on 10q and 18p provided suggestive evidence for linkage in some analyses, and, interestingly, a region on 6q, that showed only nominal significance in the original analysis, yielded increased, suggestive significance in two of the additional analyses. These regions may provide targets to focus candidate gene studies or to prioritise results from genome-wide association studies.

A new era in the genetic analysis of multiple sclerosis

PURPOSE OF REVIEW

This review covers the latest developments in the genetic analysis of multiple sclerosis in the context of advancing knowledge about the nature of complex disease. This year has seen rapid progress dominated by early applications of high-throughput single-nucleotide polymorphism typing technology.

RECENT FINDINGS

The last 12 months have seen the completion of what is probably a definitive screen for linkage, together with the beginnings of indirect full-genome screens for association with common variants. Alongside this the first ever systematic admixture mapping effort has also been completed, suggesting a possible explanation for the apparent excess of the condition in Europeans and implicating a novel susceptibility locus on chromosome 1.

SUMMARY

It is now clear that association-based studies in large cohorts will be needed to unravel the genetic basis of susceptibility to multiple sclerosis. Importantly it is also clear that the necessary tools have now arrived and that the next few years are likely to see exciting developments.

HLA‐DRB1*1501, ‐DQB1*0301, ‐DQB1*0302, ‐DQB1*0602, and ‐DQB1*0603 Alleles are Associated With More Severe Disease Outcome on Mri in Patients With Multiple Sclerosis

The most important confirmed genetic factor of susceptibility to multiple sclerosis (MS) has been identified in the HLA class II region. The hypothesis that several genes, including HLA class II, may influence the prognosis of patients with MS has been proposed. In a recent study, using low intermediate resolution typing, we found that some HLA alleles may predict disease severity as assessed by magnetic resonance imaging (MRI) measures. The aim of this study was to examine the relationship between high-resolution typing of HLA alleles and disease severity as measured by brain MRI quantitative markers of demyelinating and destructive pathology in patients with MS. In 41 MS patients (27 relapsing-remitting, 7 secondary progressive, and 7 primary progressive), we performed high-resolution typing of alleles HLA-DRB1*04, -DQB1*03, -DRB1*15, -DQB1*06, and of haplotypes -DRB1*04-DQB1*03 and -DRB1*15-DQB1*06. These alleles and haplotypes were associated with higher susceptibility to MS in a recently published case-control study conducted in the Friuli-Venezia-Giulia region, Italy. Of 41 included patients, 13 were men and 28 were women. Mean age was 43.3 (SD 11.4) years, mean disease duration 10.3 (SD 7.8) years, and mean EDSS 2.3. DNA extraction and genomic typing were obtained with the sequence-specific primers method using primer pairs that amplified the HLA alleles. All patients underwent a 1.5-T MRI examination of the brain. Disease severity was assessed by clinical measures [Expanded Disability Status Scale (EDSS)] and MRI measures. T2- and T1-lesion volumes (LVs) and brain atrophy measures [fractions of brain parenchyma (BPF), gray matter (GMF), and white matter (WMF)] were calculated. We used general linear model analysis (GML), controlled for age, disease duration, and treatment status, to compare the MRI measures according to allele and haplotype status. The following significant results were found: HLA-DRB1*1501 positive patients had significantly lower GMF (0.493 vs 0.526, p < 0.001), lower BPF (0.784 vs 0.815, p = 0.018), and higher T1-LV (2.8 vs 0.7ml, p = 0.036); -DQB1*0301 positive patients had significantly higher T2-LV (34.1 vs 0.7 ml, p = 0.041), and showed a trend for lower BPF (0.790 vs 0.846, p = 0.064); -DQB1*0302 positive patients had significantly lower T1-LV (2.4 vs 0.9 ml, p = 0.016); and -DQB1*0602 positive patients had significantly lower GMF (0.492 vs 0.521, p = 0.007) and lower BPF (0.781 vs 0.811, p = 0.023). No differences were found in the indices of MRI disease severity according to HLA haplotype associations. Both in correlation and in regression analyses, we observed significant associations between HLA-DRB1*1501 and lower GMF and BPF and higher T1-LV, between -DQB1*0301 and higher T2-LV and disease duration, between -DQB1*0302 and lower GMF and higher T1- and T2-LV, between -DQB1*0602 and lower GMF and BPF, and between -DQB1*0603 and higher T1-LV and EDSS. High-resolution HLA genotyping analysis revealed a robust relationship between alleles HLA-DRB1*1501, -DQB1*0301, -DQB1*0302, -DQB1*0602, and -DQB1*0603, and more severe damage on inflammatory and neurodegenerative MRI measures.

An investigation of polymorphisms in the 17q11.2-12 CC chemokine gene cluster for association with multiple sclerosis in Australians

Background

Multiple sclerosis (MS) is a disorder of the central nervous system (CNS) characterised by inflammation and neuronal degeneration. It is believed to result from the complex interaction of a number of genes, each with modest effect. Chemokines are vital to the migration of cells to sites of inflammation, including the CNS, and many are implicated in MS pathogenesis. Most of the CC chemokine genes are encoded in a cluster on chromosome 17q11.2-12, which has been identified in a number of genome wide screens as being potentially associated with MS.

Methods

We conducted a two-stage analysis to investigate the chemokine gene cluster for association with MS. After sequencing the chemokine genes in several DNA pools to identify common polymorphisms, 12 candidate single-nucleotide polymorphisms (SNPs) were genotyped in a cohort of Australian MS trio families.

Results

Marginally significant (uncorrected) transmission distortion was identified for four of the SNPs after stratification for several factors. We also identified marginally significant (uncorrected) transmission distortion for haplotypes encompassing the CCL2 and CCL11 genes, using two independent cohorts, which was consistent with recent reports from another group.

Conclusion

Our results implicate several chemokines as possibly being associated with MS susceptibility, and given that chemokines and their receptors are suitable targets for therapeutic agents, further investigation is warranted in this region.

Mapping candidate non-MHC susceptibility regions to multiple sclerosis

Understanding the genetic basis of multiple sclerosis (MS) remains a major challenge, despite decades of intensive research. In order to identify candidate non-MHC susceptibility regions to MS, the results of whole genome screens for linkage or association and follow-up studies in 18 different populations were superimposed together in a combined genomic map. Analysis of this map led to the prediction of at least 38 potential susceptibility regions, each showing linkage and/or association in several populations. Among these, 17 regions were the most reproducibly reported in these studies, thus representing top predicted candidates for MS. This non-formal approach to meta-analysis demonstrated the ability to verify results and retrieve lost information in an association study. Assessment of the map in a Northern Irish refined screen (n=415 cases, n=490 controls) revealed association in 15 regions (P<0.05), including 10 promising candidates on chromosomes 1p13, 2p13, 2q14, 3p23, 7q21, 13q14, 15q13, 17p13, 18q21 and 20p12 (P<0.0025). Seven of these regions were previously overlooked in the Northern Irish whole genome association study. Collating results from numerous studies, this draft map represents a tool that should facilitate the analysis of the genetic backgrounds of MS in many populations.

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

Multiple sclerosis (MS) is an autoimmune disease with overwhelming evidence for genetic determination, and for which a maternal parent-of-origin effect has been reported. As with many complex diseases, multiple suggestive linkage signals have been observed. However, the only unambiguous association and linkage identified to date is with alleles of the human lymphocyte antigen (HLA) class II region. We have now carried out high-density microsatellite genotyping for 12 of the most promising regions (1p, 1q, 2q, 4q, 5p, 9q, 10p, 11p, 12q, 17q, 18p, 19p) from a whole-genome scan in 552 affected sibling pairs. This has been carried out in 194 families containing avuncular pairs. These permit examination of parent-of-origin effects in non-colineal pairs when divided into likely maternal and paternal trait transmission. The results do not confirm any non-major histocompatibility complex linkage in the overall subset nor in the maternal, paternal or HLA-DRB1*1501 subsets. We were able to establish exclusion for a locus with lambda(AV) > or = 1.3 for all the previously suggested regions. These results again raise the possibility that the paradigm of multiple genes of small individual effect used to justify genome searches in MS is incorrect.

Allelic association of sequence variants in the herpes virus entry mediator-B gene (PVRL2) with the severity of multiple sclerosis

Discrepant findings have been reported regarding an association of the apolipoprotein E (APOE) gene with the clinical course of multiple sclerosis (MS). To resolve these discrepancies, we examined common sequence variation in six candidate genes residing in a 380-kb genomic region surrounding and including the APOE locus for an association with MS severity. We genotyped at least three polymorphisms in each of six candidate genes in 1,540 Caucasian MS families (729 single-case and multiple-case families from the United States, 811 single-case families from the UK). By applying the quantitative transmission/disequilibrium test to a recently proposed MS severity score, the only statistically significant (P=0.003) association with MS severity was found for an intronic variant in the Herpes Virus Entry Mediator-B Gene PVRL2. Additional genotyping extended the association to a 16.6 kb block spanning intron 1 to intron 2 of the gene. Sequencing of PVRL2 failed to identify variants with an obvious functional role. In conclusion, the analysis of a very large data set suggests that genetic polymorphisms in PVRL2 may influence MS severity and supports the possibility that viral factors may contribute to the clinical course of MS, consistent with previous reports.

Evaluating the role of the 620W allele of protein tyrosine phosphatase PTPN22 in Crohn's disease and multiple sclerosis

The 620W allele of PTPN22 has been associated with susceptibility to several different forms of chronic inflammatory disease, including Type 1 diabetes (T1D), rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), and autoimmune thyroiditis (AIT). We set out to explore its possible role in two other inflammatory diseases: multiple sclerosis (MS) and Crohn's disease (CD). In our cohort of 496 MS trios from the United Kingdom, we observed reduced transmission of the PTPN22 620W allele. The CD sample consisted of 169 trios as well as 249 cases of CD with their 207 matched control subjects collected in the province of Québec, Canada; there was also no evidence of association between the PTPN22 620W allele and susceptibility for CD. Pooled analyses combining our data with published data assessed a total of 1496 cases of MS and 1019 cases of CD but demonstrated no evidence of association with either disease. Given the modest odds ratios of known risk alleles for inflammatory diseases, these analyses do not exclude a role for the PTPN22 allele in susceptibility to CD or MS, but they do suggest that such a putative role would probably be more modest than that reported so far in T1D, RA, SLE, and AIT.

Gender differences in neurological disease: role of estrogens and cytokines

Increasing evidence suggests that inflammatory response may be a critical component of different brain pathologies. However, the role played by this reaction is not fully understood. The present findings suggest that neuroinflammtory mediators such as cytokines may be involved in a number of key steps in the pathological cascade of events leading to neuronal injury. This hypothesis is strongly supported by experimental and clinical observations indicating that inhibition of the inflammatory reaction correlates with less neuronal damage. Estrogens are thought to play a role in the sex difference observed in many neurological diseases with inflammatory components including stroke, Alzheimer's and Parkinson's diseases, multiple sclerosis, or amyotrophic lateral sclerosis. Clinical and experimental studies have established estrogen as a neuroprotective hormone in these diseases. However, the exact mechanisms involved in the neuroprotective effects of estrogens are still unclear. It is possible that the beneficial effects of these hormones may be dependent on their inhibitory activity on the inflammatory reaction associated with the above-mentioned brain pathologies. Here, we review the current clinical and experimental evidence with respect to the inflammation-modulating effects of estrogens as one potential explanatory factor for sexual dimorzphism in the prevalence of numerous neurological diseases.

Mapping gene activity in complex disorders: Integration of expression and genomic scans for multiple sclerosis

Genetic predisposition contributes to the pathogenesis of most common diseases. Genetic studies have been extremely successful in the identification of genes responsible for a number of Mendelian disorders. However, with a few exceptions, genes predisposing to diseases with complex inheritance remain unknown despite multiple efforts. In this article we collected detailed information for all genome-wide genetic screens performed to date in multiple sclerosis (MS) and in its animal model experimental autoimmune encephalomyelitis (EAE), and integrated these results with those from all high throughput gene expression studies in humans and mice. We analyzed a total of 55 studies. We found that differentially expressed genes (DEG) are not uniformly distributed in the genome, but rather appear in clusters. Furthermore, these clusters significantly differ from the known heterogeneous organization characteristic of eukaryotic gene distributions. We also identified regions of susceptibility that overlapped with clusters of DEG leading to the prioritization of candidate genes. Integration of genomic and transcriptional information is a powerful tool to dissect genetic susceptibility in complex multifactorial disorders like MS.

Fine mapping of the multiple sclerosis susceptibility locus on 5p14-p12

Linkage analyses have identified four major MS susceptibility loci in Finns. Here we have fine mapped the region on chromosome 5p in 28 Finnish MS families. Marker D5S416 provided the highest pairwise LOD score, and multipoint and haplotype analyses restrict the critical region to about 5.3 Mb on 5p15 between markers D5S1987 and D5S416. Ascertaining for HLA type and geographical origin indicated that families with and without the HLA DR15 risk haplotype, as well as families within and outside an internal high-risk region, contributed to the linkage to 5p, implying the general significance for this locus in Finnish MS families.

An investigation of NOS2A promoter polymorphisms in Australian multiple sclerosis patients

As with other major autoimmune diseases, susceptibility to multiple sclerosis (MS) is believed to result from the complex interaction of a number of genes, each with modest effect. Extensive research of experimental autoimmune encephalomyelitis in mice and several direct MS studies have implicated NOS2A, which encodes the inducible form of nitric oxide synthase, and the genetic region encoding NOS2A, 17q11.2, has been identified in a number of genome wide screens as being potentially associated with MS. We investigated four single nucleotide polymorphisms in the proximal promoter region of NOS2A, in a case-control group of 100 Australian MS patients and 100 controls and in 203 MS patients and their unaffected parents. We found a trend toward excess transmission of the -277A allele (tag for the AGCC haplotype) to HLA-DRB1*1501-positive MS patients (P (uncorrected)=0.05). We initially discovered a trend toward over-representation of the AGCC haplotype in HLA-DRB1*1501-positive compared to HLA-DRB1*1501-negative MS patients in the case-control cohort. However, when combined with the probands from the transmission disequilibrium analysis, this trend was nullified. Nonetheless, despite the lack of significant evidence of association for the NOS2A promoter polymorphisms with MS, the gene remains an interesting candidate for MS susceptibility, particularly with regard to the HLA-DRB1*1501 haplotype.

A high-density screen for linkage in multiple sclerosis

To provide a definitive linkage map for multiple sclerosis, we have genotyped the Illumina BeadArray linkage mapping panel (version 4) in a data set of 730 multiplex families of Northern European descent. After the application of stringent quality thresholds, data from 4,506 markers in 2,692 individuals were included in the analysis. Multipoint nonparametric linkage analysis revealed highly significant linkage in the major histocompatibility complex (MHC) on chromosome 6p21 (maximum LOD score [MLS] 11.66) and suggestive linkage on chromosomes 17q23 (MLS 2.45) and 5q33 (MLS 2.18). This set of markers achieved a mean information extraction of 79.3% across the genome, with a Mendelian inconsistency rate of only 0.002%. Stratification based on carriage of the multiple sclerosis-associated DRB1*1501 allele failed to identify any other region of linkage with genomewide significance. However, ordered-subset analysis suggested that there may be an additional locus on chromosome 19p13 that acts independent of the main MHC locus. These data illustrate the substantial increase in power that can be achieved with use of the latest tools emerging from the Human Genome Project and indicate that future attempts to systematically identify susceptibility genes for multiple sclerosis will have to involve large sample sizes and an association-based methodology.

Interaction of loci within the HLA region influences multiple sclerosis course in the Sardinian population

We examined the influence of alleles at the HLA loci, previously found to be associated with multiple sclerosis (MS) in Sardinia, on the clinical course of the disease in 835 relapsing (R) and 100 primary progressive (PP) patients. Multivariate analysis was carried out on predisposing 0301 or non-associated DPB1 alleles, susceptible or non-associated DRB1-DQB1 haplotypes, both predisposing and non-predisposing, and negatively and non-negatively associated D6S1683 alleles, taking interaction between them into account. Intra-patient analysis showed that the presence of the susceptible or protective D6S1683 allele interacting with predisposing DP 0301 modulated risk of PP disease. These findings suggest that a locus telomeric to HLA class I exerts an effect on alleles at the DPB1 locus in modulating disease course.

A second-generation genomic screen for multiple sclerosis

Multiple sclerosis (MS) is a debilitating neuroimmunological and neurodegenerative disorder. Despite substantial evidence for polygenic inheritance of the disease, the major histocompatibility complex is the only region that clearly and consistently demonstrates linkage and association in MS studies. The goal of this study was to identify additional chromosomal regions that harbor susceptibility genes for MS. With a panel of 390 microsatellite markers genotyped in 245 U.S. and French multiplex families (456 affected relative pairs), this is the largest genomic screen for MS conducted to date. Four regions met both of our primary criteria for further interest (heterogeneity LOD [HLOD] and Z scores >2.0): 1q (HLOD=2.17; Z=3.38), 6p (HLOD=4.21; Z=2.26), 9q (HLOD; Z=2.71), and 16p (HLOD=2.64; Z=2.05). Two additional regions met only the Z score criterion: 3q (Z=2.39) and 5q (Z=2.17). Further examination of the data by country (United States vs. France) identified one additional region demonstrating suggestive linkage in the U.S. subset (18p [HLOD=2.39]) and two additional regions generating suggestive linkage in the French subset (1p [HLOD=2.08] and 22q [HLOD=2.06]). Examination of the data by human leukocyte antigen (HLA)-DR2 stratification identified four additional regions demonstrating suggestive linkage: 2q (HLOD=3.09 in the U.S. DR2- families), 6q (HLOD=3.10 in the French DR2- families), 13q (HLOD=2.32 in all DR2+ families and HLOD=2.17 in the U.S. DR2+ families), and 16q (HLOD=2.32 in all DR2+ families and HLOD=2.13 in the U.S. DR2+ families). These data suggest several regions that warrant further investigation in the search for MS susceptibility genes.

A meta-analysis of whole genome linkage screens in multiple sclerosis

Linkage studies in complex diseases like multiple sclerosis, where the effects attributable to individual loci are modest, are critically dependent upon the number of families included. We have combined the raw genotyping data from all published genome linkage screens in multiple sclerosis and thereby performed a linkage analysis including 719 families studied with a weighted average of 359 microsatellite markers per family (range 257-453) providing an average marker separation of 10.2 cM. Linkage with genome-wide significance is confirmed in the HLA region on chromosome 6p21. In addition, two novel regions suggestive of linkage are seen (17q21 and 22q13). Our simulations would imply that the number of peaks with NPL scores >/=2.1 exceeds the number expected by chance alone.

Refining the linkage analysis on chromosome 10 in 449 sib-pairs with multiple sclerosis

Genome-wide screens for linkage in multiplex families with multiple sclerosis (MS) from United Kingdom, Sardinia, Italy and the Nordic countries (Denmark, Finland, Norway and Sweden) have each shown suggestive or potential linkage on chromosome 10. The partially overlapping regions identified by these studies encompass around 60 cM of the chromosome. In order to explore this region further, we typed 13 microsatellite markers in the same 449 families originally studied in the individual screens. This additional genotyping increased the information extraction in the region from 52% to 79% and revealed increased support for linkage (MLS 2.5) peaking at 10p15.