Multiple Sclerosis Families Research Articles

Familial Mediterranean fever-associated mutation pyrin E148Q as a potential risk factor for multiple sclerosis

Background: Familial Mediterranean fever (FMF) is an inherited autoinflammatory disease caused by mutations in the MEFV gene and characterized by recurrent febrile polyserositis. A possible association of FMF and multiple sclerosis (MS) has been suggested in cohorts from Turkey and Israel. Objective: The objective of this study was to investigate the prevalence of MEFV mutations in subjects with MS and in controls in Germany. Methods: One-hundred and fifty seven MS patients with at least one symptom or without symptoms suggestive of FMF from our outpatient clinic were investigated for mutations in exons 2, 3, and 10 of the MEFV gene (group 1). 260 independent MS patients (group 2) and 400 unrelated Caucasian controls (group 3) were screened selectively for the low-penetrance pyrin mutations E148Q and K695R Results: In group 1, 19 MS patients (12.1%) tested positive for a mutation in the MEFV gene, mainly the E148Q (n=7) substitution. Fifteen of the 19 mutation-positive individuals reported at least one symptom suggestive of FMF. In three cases, we could identify additional family members with MS. In these pedigrees, the E148Q exchange co-segregated with MS (p=0.026). Frequencies of the pyrin E148Q and K695R mutations were not statistically different between MS group 2 and controls but they occurred with a surprisingly high frequency in the German population. Conclusion: The MEFV gene appears to be another immunologically relevant gene locus which contributes to MS susceptibility. In particular, the pyrin E148Q mutation, which co-segregated with disease in three MS families, is a promising candidate risk factor for MS that should be further explored in larger studies.

Cortical Pathology in RRMS: Taking a Cue from Four Sisters

Background. Although grey matter pathology is a relevant aspect of multiple sclerosis (MS) both with physical and cognitive rebounds, its pathogenesis is still under investigation. To what extent the familial and sporadic cases of MS differ in cortical pathology has not been elucidated yet. Here we present a multiple case report of four sisters affected by MS, all of them having a very high burden of cortical pathology. Methods. The clinical and grey matter MRI parameters of the patients were compared with those of twenty-five-aged matched healthy women and 25 women affected by sporadic MS (matched for age, disease duration, EDSS, and white matter lesion load). Results. Despite their short disease duration (<5 years), the four sisters showed a significant cortical thinning compared to healthy controls (P = 0.003) and sporadic MS (P = 0.041) and higher CLs number (P < 0.001) and volume (P < 0.001) compared to sporadic MS. Discussion. Although limited to a single family, our observation is worth of interest since it suggests that familial factors may account for a peculiar involvement of the cortex in MS pathology. This hypothesis should be further evaluated in a large number of multiplex MS families.

TCRBV20S1 polymorphism does not influence the susceptibility to type 1 diabetes and multiple sclerosis in the Sardinian population

Among the different T-cell receptor (TCR) BV20S1 polymorphisms, nucleotide substitution at position 524 results in the introduction of a stop codon, whose potential functional relevance is still unknown. We have recently showed in Sardinian subjects the most elevated allele frequency ever reported worldwide for this "null allele" (0.44). As this variant generates a gap in the TCR repertoire, this preliminary finding prompted us to further analyze the role of this polymorphism in the susceptibility to type 1 diabetes (T1D) and multiple sclerosis (MS), which are extremely common in this population. With this aim, we evaluated the influence of the TCRBV20S1 polymorphism by assessing it with the transmission disequilibirum test (TDT) in 652 T1D and 616 MS families, without detecting any significant difference. We conclude that the high frequency of this null allele in Sardinia is not directly related to the high incidence of these autoimmune diseases observed in this founder population.

MHC transmission

Major histocompatibility complex (MHC) genes dominate genetic susceptibility factors in multiple sclerosis (MS). Given the general consensus that incidence and prevalence of MS has been rising and specifically in women, we evaluated MHC-gender interactions. In a large family-based cohort consisting of 7,093 individuals (2,127 affected individuals) from 1,055 MS families, we examined MHC transmission by family structure and gender stratified by genetic distance of affected relatives from the MS proband. We found that affected individuals with HLA-DRB1*15-positive genotypes have higher female-to-male ratios as compared with affected individuals with HLA-DRB1*15-negative genotypes (χ(2) = 9.97, p = 0.0015) with the exception of multiplex families with 3 or more affected across 2 generations. Transmission disequilibrium test results show that HLA-DRB1*15 transmission was more distorted in collateral families vs nuclear families (χ(2) = 8.030, p = 0.0046), exclusively in affected female-female pairs (χ(2) = 7.81, p = 0.0051), but not in mixed gender pairs (χ(2) = 1.58, p = 0.21) or matched male pairs (Fisher p = 0.21). These observations implicate the MHC as the site of interactions and modifications mediating the female-to-male gender ratio in MS and its progressive increase. They further suggest this occurs via gene-environment interactions and epigenetic modifications in this region. The difference between collateral and nuclear families provides some insight into the inheritance, decay, and gender specificity of putative epigenetic marks.

Aggregation of multiple sclerosis genetic risk variants in multiple and single case families

Multiple sclerosis (MS) is a multifactorial neurologic disease characterized by modest but tractable heritability. Genome-wide association studies have identified and/or validated multiple polymorphisms in approximately 16 genes associated with susceptibility. We aimed at investigating the aggregation of genetic MS risk markers in individuals by comparing multiple- and single-case families. A weighted log-additive integrative approach termed MS genetic burden (MSGB) was used to account for the well-established genetic variants from previous association studies and meta-analyses. The corresponding genetic burden and its transmission was analyzed in 1,213 independent MS families (810 sporadic and 403 multicase families). MSGB analysis demonstrated a higher aggregation of susceptibility variants in multicase compared to sporadic MS families. In addition, the aggregation of non-major histocompatibility complex single nucleotide polymorphisms depended neither on gender nor on the presence or absence of HLA-DRB1*15:01 alleles. Interestingly, although a greater MSGB in siblings of MS patients was associated with an increased risk of MS (odds ratio, 2.1; p = 0.001), receiver operating characteristic curves of MSGB differences between probands and sibs (area under the receiver operator curves, 0.57 [95% confidence interval, 0.53-0.61]) show that case-control status prediction of MS cannot be achieved with the currently available genetic data. The primary interest in the MSGB concept resides in its capacity to integrate cumulative genetic contributions to MS risk. This analysis underlines the high variability of family load with known common variants. This novel approach can be extended to other genetically complex diseases. Despite the emphasis on assembling large case-control datasets, multigenerational, multiaffected families remain an invaluable resource for advancing the understanding of the genetic architecture of complex traits.

Parent-of-origin effects at the major histocompatibility complex in multiple sclerosis

Multiple sclerosis (MS) susceptibility is characterized by maternal parent-of-origin effects and increased female penetrance. In 7796 individuals from 1797 MS families (affected individuals n = 2954), we further implicate epigenetic modifications within major histocompatibility complex (MHC) class II haplotypes as mediating these phenomena. Affected individuals with the main MS-associated allele HLA-DRB1*15 had a higher female-to-male ratio versus those lacking it (P = 0.00023). Distorted transmission of MHC haplotypes by both parent-of-origin and gender-of-affected-offspring was most evident in the maternal HLA-DRB1*15 transmission to affected female offspring (OR = 3.31, 95% CI = 2.59-4.24) contrasting with similarity among maternal transmission to affected male offspring (OR = 2.13, 95% CI = 1.44-3.14), paternal transmissions to affected female (OR = 2.14, 95% CI = 1.64-2.78) and male (OR = 2.16, 95% CI = 1.37-3.39) offspring. Significant parent-of-origin effects were observed in affected females (maternal: P = 9.33 x 10(-42); paternal: P = 1.12 x 10(-15); comparison: P = 0.0014), but not in affected males (maternal: P = 6.70 x 10(-8); paternal: P = 2.54 x 10(-6); comparison: P = 0.95). Conditional logistic regression analysis revealed further differential risk of HLA diplotypes. Risks for HLA-DRB1*15 and likely for other HLA-DRB1 haplotypes were restricted by (i) parent-of-origin, (ii) gender-of-offspring and (iii) trans epistasis in offspring. These findings may illuminate the gender bias characterizing autoimmunity overall. They raise questions about the concept of restricted antigen presentation in autoimmunity and suggest that gender-specific epigenetic interactions may be the driving forces behind the MHC haplotypic associations. Haplotype-specific epigenetic modifications at MHC class II and their decay appear to be at the heart of MS pathogenesis and inheritance of risk, providing the focus for gene-environment interactions that determine susceptibility and resistance.

Genome-wide Association Study in a High-Risk Isolate for Multiple Sclerosis Reveals Associated Variants in STAT3 Gene

Genetic risk for multiple sclerosis (MS) is thought to involve both common and rare risk alleles. Recent GWAS and subsequent meta-analysis have established the critical role of the HLA locus and identified new common variants associated to MS. These variants have small odds ratios (ORs) and explain only a fraction of the genetic risk. To expose potentially rare, high-impact alleles, we conducted a GWAS of 68 distantly related cases and 136 controls from a high-risk internal isolate of Finland with increased prevalence and familial occurrence of MS. The top 27 loci with p < 10(-4) were tested in 711 cases and 1029 controls from Finland, and the top two findings were validated in 3859 cases and 9110 controls from more heterogeneous populations. SNP (rs744166) within the STAT3 gene was associated to MS (p = 2.75 x 10(-10), OR 0.87, confidence interval 0.83-0.91). The protective haplotype for MS in STAT3 is a risk allele for Crohn disease, implying that STAT3 represents a shared risk locus for at least two autoimmune diseases. This study also demonstrates the potential of special isolated populations in search for variants contributing to complex traits.

The family of the multiple sclerosis patient: A psychosocial perspective

The present review addresses some of the issues pertaining to the family whose member suffers from multiple sclerosis (MS), the implications that arise, and the potential therapeutic interventions. The family role can be better conceptualized from a psychosocial view mainly in a systemic perspective. From this point of view, MS can be classified, in the context of chronic illnesses, according to several ‘non-medical’ characteristics of the disease, such as age at onset and course. Furthermore, MS challenges the individual roles, needs and coping styles of all members of the family, and establishes a frail balance in the relationships, which needs to be reset. Future research ought to focus on specific problems, such as the identification of members of MS families at risk of developing depression and anxiety, and application of the optimal psychotherapeutic interventions. Research on psychosocial and psycho-educational interventions that improve social support and decrease burden of illness would certainly ameliorate clinical practice.

Use of a genetic isolate to identify rare disease variants: C7 on 5p associated with MS

Large case-control genome-wide association studies primarily expose common variants contributing to disease pathogenesis with modest effects. Thus, alternative strategies are needed to tackle rare, possibly more penetrant alleles. One strategy is to use special populations with a founder effect and isolation, resulting in allelic enrichment. For multiple sclerosis such a unique setting is reported in Southern Ostrobothnia in Finland, where the prevalence and familial occurrence of multiple sclerosis (MS) are exceptionally high. Here, we have studied one of the best replicated MS loci, 5p, and monitored for haplotypes shared among 72 regional MS cases, the majority of which are genealogically distantly related. The haplotype analysis over the 45 Mb region, covering the linkage peak identified in Finnish MS families, revealed only modest association at IL7R (P = 0.04), recently implicated in MS, whereas most significant association was found with one haplotype covering the C7-FLJ40243 locus (P = 0.0001), 5.1 Mb centromeric of IL7R. The finding was validated in an independent sample from the isolate and resulted in an odds ratio of 2.73 (P = 0.000003) in the combined data set. The identified relatively rare risk haplotype contains C7 (complement component 7), an important player of the innate immune system. Suggestive association with alleles of the region was seen also in more heterogeneous populations. Interestingly, also the complement activity correlated with the identified risk haplotype. These results suggest that the MS predisposing locus on 5p is more complex than assumed and exemplify power of population isolates in the identification of rare disease alleles.

MYO9B polymorphisms in multiple sclerosis

Single-nucleotide polymorphisms (SNPs) in the 3' region of myosin IXB (MYO9B) gene have recently been reported to associate with different inflammatory or autoimmune diseases. We monitored for the association of MYO9B variants to multiple sclerosis (MS) in four Northern European populations. First, 18 SNPs including 6 SNPs with previous evidence for association to immune disorders, were tested in 730 Finnish MS families, but no linkage or family-based association was observed. To ensure the power to detect variants with a modest effect size, we further analyzed 10 variants in 899 Finnish cases and 1325 controls, and in a total of 1521 cases and 1476 controls from Denmark, Norway and Sweden, but found no association. Our results thereby do not support a major function of the tested MYO9B variants in MS.

HLA class I alleles tag HLA-DRB1 * 1501 haplotypes for differential risk in multiple sclerosis susceptibility

The major locus for multiple sclerosis (MS) susceptibility is located within the class II region of the Major Histocompatibility Complex (MHC). HLA-DRB1 alleles, constituting the strongest MS susceptibility factors, have been widely exploited in research including construction of transgenic animal models of MS. Many studies have concluded that HLA-DRB1*15 allele itself determines MS-associated susceptibility. If this were true, haplotypes bearing this allele would confer equal risk. If HLA-DRB1*15 bearing haplotypes differed for risk, roles for other loci in this region would be implied and further study of the fine structure of this locus would be compelling. We have tested the hypothesis comparing haplotypes stratified by HLA class I tagging. We show here that HLA-DRB1*15-bearing-haplotypes in 1970 individuals from 494 MS families are indeed heterogeneous. Some HLA-DRB1*15 haplotypes determine susceptibility while others do not. Three groups of class I tagged HLA-DRB1*15 haplotypes were not over-transmitted: (i) HLA-DRB1*15-HLA-B*08 (TR = 25, NT = 23, Odds Ratio = 1.09), (ii) -HLA-B*27 (TR = 18, NT = 17, Odds Ratio = 1.06), and (iii) rare HLA-DRB1*15 haplotypes (frequency <0.02). Rare haplotypes were significantly different from common haplotypes, and transmissions were remarkably similar to those for class-I-matched non-HLA-DRB1*15 haplotypes. These results unambiguously indicate that HLA-DRB1*15 is part of a susceptibility haplotype but cannot be the susceptibility allele itself, requiring either epistatic interactions, epigenetic modifications on some haplotypes, or nearby structural variation. These findings strongly imply that differences among HLA-DRB1*15 haplotypes will furnish the basis for MHC-associated susceptibility in MS and raise the possibility that the MHC haplotype is the fundamental unit of genetic control of immune response.

Genetic variation in nitric oxide synthase 2A (NOS2A) and risk for multiple sclerosis

Multiple sclerosis (MS) is a chronic inflammatory disorder of the central nervous system with a strong genetic component. Variation in the major histocompatibility complex on chromosome 6p21, specifically the HLA-DRB1*15 haplotype, is the strongest genetic factor for MS, yet it is estimated to account for only a portion of risk for the disease. Previous evidence has implicated the nitric oxide synthase gene (NOS2A) encoding inducible NOS on chromosome 17q11 as a potential MS susceptibility gene. To determine whether variation in the NOS2A gene contributes to MS risk, we investigated a total of 50 polymorphisms within or flanking the locus for evidence of association using a comprehensive analytical strategy. A total of 6265 members from 1858 well-characterized MS families were utilized. No evidence for overtransmission of any individual single-nucleotide polymorphism allele or haplotype to the MS-affected individuals was observed. Furthermore, different transmission rates were not observed in either DRB1*15-positive or DRB1*15-negative family subgroups, or when extreme clinical outcomes characterizing disease progression were examined. The very largest study of NOS2A variation in MS, to date, excludes even a modest role for this locus in susceptibility.

Parent-of-origin effects in MS

Multiple sclerosis (MS) is a complex neurologic disease of unknown etiology and inheritance pattern, but with increasing incidence among females. The study of aunt/uncle-niece/nephew (AUNN) pairs has potential to shed light on the on complex trait inheritance as this group can be divided into eight different pair types by gender, MS status, and parent of origin. Using a cohort of 807 avuncular MS families with 938 affected AUNN pairs ascertained from a longitudinal, population-based Canadian database, we examined differential MS transmission by separating affected pairs into likely maternal and paternal trait origin. We observed an increased number of avuncular pairs connected through unaffected mothers compared to unaffected fathers (p = 0.008). To restrict confounders introduced by families with multiple pairs the overall number of maternal and paternal families were compared, to reveal a significantly higher number of maternal families (p = 0.038). Female-to-male sex ratios were higher among affected nieces/nephews when compared to the sex ratio for aunts/uncles (0.00042). This observation independently confirms previous findings of a "maternal parent-of-origin" effect in multiple sclerosis (MS) susceptibility. These findings highlight the special contribution that can be derived from avuncular pairs. These underutilized pairings can compare transmission by the gender of affected aunt-uncle, the unaffected transmitting parent, and by that of the affected offspring. This strategy may be especially profitable in diseases where parent-of-origin effects are being sought. These findings also independently confirm the increasing rate of MS in females, demonstrating that familial cases are influenced by the same environmental factors as the general MS population.

Parental non-inherited HLA resistance alleles do not confer protection against multiple sclerosis

Multiple sclerosis (MS) is a complex trait in which alleles at or near the class II loci HLA-DRB1 and HLA-DQB1 contribute significantly to genetic risk. HLA-DRB1⁎14 and DRB1⁎11 bearing haplotypes protect against MS and DRB1⁎01 and DRB1⁎10 interact with DRB1⁎15 to reduce risk of the disease. Recent work in other autoimmune diseases such as rheumatoid arthritis has suggested that maternal non-transmitted protective alleles can also confer disease resistance. In this investigation of 7093 individuals from 1432 MS families, we have analysed the transmission of HLA-DRB1⁎14, ⁎11, ⁎10 and ⁎01 haplotypes, stratified by sex of parent. No significant transmission differences between mothers and fathers were found, suggesting that non-inherited resistance alleles do not appear to play a role in MS.

Genetic loci linked to Type 1 Diabetes and Multiple Sclerosis families in Sardinia

BackgroundThe Mediterranean island of Sardinia has a strikingly high incidence of the autoimmune disorders Type 1 Diabetes (T1D) and Multiple Sclerosis (MS). Furthermore, the two diseases tend to be co-inherited in the same individuals and in the same families. These observations suggest that some unknown autoimmunity variant with relevant effect size could be fairly common in this founder population and could be detected using linkage analysis.MethodsTo search for T1D and MS loci as well as any that predispose to both diseases, we performed a whole genome linkage scan, sequentially genotyping 593 microsatellite marker loci in 954 individuals distributed in 175 Sardinian families. In total, 413 patients were studied; 285 with T1D, 116 with MS and 12 with both disorders. Model-free linkage analysis was performed on the genotyped samples using the Kong and Cox logarithm of odds (LOD) score statistic.ResultsIn T1D, aside from the HLA locus, we found four regions showing a lod-score ≥1; 1p31.1, 6q26, 10q21.2 and 22q11.22. In MS we found three regions showing a lod-score ≥1; 1q42.2, 18p11.21 and 20p12.3. In the combined T1D-MS scan for shared autoimmunity loci, four regions showed a LOD >1, including 6q26, 10q21.2, 20p12.3 and 22q11.22. When we typed more markers in these intervals we obtained suggestive evidence of linkage in the T1D scan at 10q21.2 (LOD = 2.1), in the MS scan at 1q42.2 (LOD = 2.5) and at 18p11.22 (LOD = 2.6). When all T1D and MS families were analysed jointly we obtained suggestive evidence in two regions: at 10q21.1 (LOD score = 2.3) and at 20p12.3 (LOD score = 2.5).ConclusionThis suggestive evidence of linkage with T1D, MS and both diseases indicates critical chromosome intervals to be followed up in downstream association studies.

Parental transmission of HLA-DRB1*15 in multiple sclerosis

Multiple sclerosis (MS) is a complex trait in which HLA-DRB1*15 bearing MHC haplotypes increase risk of MS in people of Northern European descent. In this investigation of 7,334 individuals from 1,515 MS families, the largest cohort used to study the HLA-DRB1 locus to date, we analysed the transmission of HLA-DRB1*15 haplotypes stratified by sex of transmitting parent. A significant over transmission of HLA-DRB1*15 from mothers was observed (chi (2) = 7.73, P = 0.0054), suggesting that parent of origin effects at the MHC determine susceptibility to MS.

SNP mapping and candidate gene sequencing in the class I region of the HLA complex: searching for multiple sclerosis susceptibility genes in Tasmanians

This study is an extension to previously published work that has linked variation in the human leukocyte antigen (HLA) class I region with susceptibility to multiple sclerosis (MS) in Australians from the Island State of Tasmania. Single nucleotide polymorphism (SNP) mapping was performed on an 865-kb candidate region (D6S1683-D6S265) in 166 Tasmanian MS families, and seven candidate genes [ubiquitin D (UBD), olfactory receptor 2H3 (OR2H3), gamma-aminobutyric acid B receptor 1 (GABBR1), myelin oligodendrocyte glycoprotein (MOG), HLA-F, HLA complex group 4 (HCG4) and HLA-G] were resequenced. SNPs tagging the extended MS susceptibility haplotype were genotyped in an independent sample of 356 Australian MS trios and SNPs in the MOG gene were significantly over-transmitted to MS cases. We identified significant effects on MS susceptibility of HLA-A*2 (OR: 0.51; P = 0.05) and A*3 (OR: 2.85; P = 0.005), and two coding polymorphisms in the MOG gene (V145I: P = 0.01, OR: 2.2; V142L: P = 0.04, OR: 0.45) after full conditioning on HLA-DRB1. We have therefore identified plausible candidates for the causal MS susceptibility allele, and although not conclusive at this stage, our data provide suggestive evidence for multiple class I MS susceptibility genes.

The Inheritance of Resistance Alleles in Multiple Sclerosis

Multiple sclerosis (MS) is a complex trait in which alleles at or near the class II loci HLA-DRB1 and HLA-DQB1 contribute significantly to genetic risk. HLA-DRB1*15 and HLA-DRB1*17-bearing haplotypes and interactions at the HLA-DRB1 locus increase risk of MS but it has taken large samples to identify resistance HLA-DRB1 alleles. In this investigation of 7,093 individuals from 1,432 MS families, we have assessed the validity, mode of inheritance, associated genotypes, and the interactions of HLA-DRB1 resistance alleles. HLA-DRB1*14-, HLA-DRB1*11-, HLA-DRB1*01-, and HLA-DRB1*10-bearing haplotypes are protective overall but they appear to operate by different mechanisms. The first type of resistance allele is characterised by HLA-DRB1*14 and HLA-DRB1*11. Each shows a multiplicative mode of inheritance indicating a broadly acting suppression of risk, but a different degree of protection. In contrast, a second type is exemplified by HLA-DRB1*10 and HLA-DRB1*01. These alleles are significantly protective when they interact specifically in trans with HLA-DRB1*15-bearing haplotypes. HLA-DRB1*01 and HLA-DRB1*10 do not interact with HLA-DRB1*17, implying that several mechanisms may be operative in major histocompatibility complex–associated MS susceptibility, perhaps analogous to the resistance alleles. There are major practical implications for risk and for the exploration of mechanisms in animal models. Restriction of antigen presentation by HLA-DRB1*15 seems an improbably simple mechanism of major histocompatibility complex–associated susceptibility.

SNPs in Multi-Species Conserved Sequences (MCS) as useful markers in association studies: a practical approach

BackgroundAlthough genes play a key role in many complex diseases, the specific genes involved in most complex diseases remain largely unidentified. Their discovery will hinge on the identification of key sequence variants that are conclusively associated with disease. While much attention has been focused on variants in protein-coding DNA, variants in noncoding regions may also play many important roles in complex disease by altering gene regulation. Since the vast majority of noncoding genomic sequence is of unknown function, this increases the challenge of identifying "functional" variants that cause disease. However, evolutionary conservation can be used as a guide to indicate regions of noncoding or coding DNA that are likely to have biological function, and thus may be more likely to harbor SNP variants with functional consequences. To help bias marker selection in favor of such variants, we devised a process that prioritizes annotated SNPs for genotyping studies based on their location within Multi-species Conserved Sequences (MCSs) and used this process to select SNPs in a region of linkage to a complex disease. This allowed us to evaluate the utility of the chosen SNPs for further association studies. Previously, a region of chromosome 1q43 was linked to Multiple Sclerosis (MS) in a genome-wide screen. We chose annotated SNPs in the region based on location within MCSs (termed MCS-SNPs). We then obtained genotypes for 478 MCS-SNPs in 989 individuals from MS families.ResultsAnalysis of our MCS-SNP genotypes from the 1q43 region and comparison to HapMap data confirmed that annotated SNPs in MCS regions are frequently polymorphic and show subtle signatures of selective pressure, consistent with previous reports of genome-wide variation in conserved regions. We also present an online tool that allows MCS data to be directly exported to the UCSC genome browser so that MCS-SNPs can be easily identified within genomic regions of interest.ConclusionOur results showed that MCS can easily be used to prioritize markers for follow-up and candidate gene association studies. We believe that this novel approach demonstrates a paradigm for expediting the search for genes contributing to complex diseases.

Transmission of class I/II multi-locus MHC haplotypes and multiple sclerosis susceptibility: accounting for linkage disequilibrium

The human major histocompatibility complex (MHC) class II region is associated with genetic susceptibility to multiple sclerosis (MS). Roles for HLA class I loci have been supported in several case-control studies, but this methodology does not consider the known linkage disequilibrium (LD) between class I and II loci. In 1258 individuals from 294 MS families, we analysed class I and II interactions. Using transmission disequilibrium test and haplotype analyses, we found positive associations between MS and several HLA-DRB1*15-HLA-A haplotypes including HLA-DRB1*15-HLA-A*02 (P = 2.41 x 10(-5)) and -HLA-A*03 (P = 8.42 x 10(-6)) and several HLA-DRB1*15-HLA-B haplotypes including HLA-DRB1*15-HLA-B*07 (P = 2.23 x 10(-10)). HLA-DRB1*15 haplotypes divergent for reported HLA-A allelic associations were equally over-transmitted, illustrating no detectable effect of HLA-A or -B alleles in cis on susceptibility. HLA-A and -B alleles on haplotypes not bearing HLA-DRB1*15 were not over-transmitted. Similarly, general over-transmission of HLA-DRB1*15 haplotypes was independent of the HLA-B allele present. Furthermore, HLA-B*07 haplotypes from HLA-DRB1*X-HLA-B*X/HLA-DRB1*X-HLA-B*07 heterozygous parents were transmitted per random expectation giving no indication of HLA-B independence or trans complementation of HLA-DRB1*15 by HLA-DRB1*X-HLA-B*07 haplotypes. These results imply that many reports of class I allelic associations in MS are class II dependent, secondary to LD with class II loci. The lack of independent class I associations suggests that virus-related class I-antigen complexes are not T-cell targets in MS. The inability to replicate confirmed case-control associations highlights the importance of family-based analyses. The frequency of allelic associations not being replicated emphasizes the requirement for constructing multi-locus haplotypes in dissecting associations in regions of tight LD.