A full genome search in multiple sclerosis

Central nervous system recruitment of effector memory CD8+ T lymphocytes during neuroinflammation is dependent on α4 integrin

Clonally expanded CD8⁺ T lymphocytes are present in multiple sclerosis lesions, as well as in the cerebrospinal fluid of patients with multiple sclerosis. In experimental autoimmune encephalomyelitis, CD8⁺ T lymphocytes are found in spinal cord and brainstem lesions. However, the exact phenotype of central nervous system-infiltrating CD8⁺ T lymphocytes and the mechanism by which these cells cross the blood–brain barrier remain largely unknown. Using cerebrospinal fluid from patients with multiple sclerosis, spinal cord from experimental autoimmune encephalomyelitis and coronavirus-induced encephalitis, we demonstrate that central nervous system-infiltrating CD8⁺ T lymphocytes are mostly of the effector memory phenotype (CD62L⁻ CCR7⁻ granzymeB^hi). We further show that purified human effector memory CD8⁺ T lymphocytes transmigrate more readily across blood-brain barrier-endothelial cells than non-effector memory CD8⁺ T lymphocytes, and that blood-brain barrier endothelium promotes the selective recruitment of effector memory CD8⁺ T lymphocytes. Furthermore, we provide evidence for the recruitment of interferon-γ- and interleukin-17-secreting CD8⁺ T lymphocytes by human and mouse blood-brain barrier endothelium. Finally, we show that in vitro migration of CD8⁺ T lymphocytes across blood-brain barrier-endothelial cells is dependent on α4 integrin, but independent of intercellular adhesion molecule-1/leucocyte function-associated antigen-1, activated leucocyte cell adhesion molecule/CD6 and the chemokine monocyte chemotactic protein-1/CCL2. We also demonstrate that in vivo neutralization of very late antigen-4 restricts central nervous system infiltration of CD8⁺ T lymphocytes in active immunization and adoptive transfer experimental autoimmune encephalomyelitis, and in coronavirus-induced encephalitis. Our study thus demonstrates an active role of the blood-brain barrier in the recruitment of effector memory CD8⁺ T lymphocytes to the CNS compartment and defines α4 integrin as a major contributor of CD8⁺ T lymphocyte entry into the brain.

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.

A distinct role of CD4+ Th17- and Th17-stimulated CD8+ CTL in the pathogenesis of type 1 diabetes and experimental autoimmune encephalomyelitis

Both CD4(+) Th17-cells and CD8(+) cytotoxic T lymphocytes (CTLs) are involved in type 1 diabetes and experimental autoimmune encephalomyelitis (EAE). However, their relationship in pathogenesis of these autoimmune diseases is still elusive. We generated ovalbumin (OVA)- or myelin oligodendrocyte glycoprotein (MOG)-specific Th17 cells expressing RORγt and IL-17 by in vitro co-culturing OVA-pulsed and MOG(35-55) peptide-pulsed dendritic cells (DC(OVA) and DC(MOG)) with CD4(+) T cells derived from transgenic OTII and MOG-T cell receptor mice, respectively. We found that these Th17 cells when transferred into C57BL/6 mice stimulated OVA- and MOG-specific CTL responses, respectively. To assess the above question, we adoptively transferred OVA-specific Th17 cells into transgenic rat insulin promoter (RIP)-mOVA mice or RIP-mOVA mice treated with anti-CD8 antibody to deplete Th17-stimulated CD8(+) T cells. We demonstrated that OVA-specific Th17-stimulated CTLs, but not Th17 cells themselves, induced diabetes in RIP-mOVA. We also transferred MOG-specific Th17 cells into C57BL/6 mice and H-2K(b-/-) mice lacking of the ability to generate Th17-stimulated CTLs. We further found that MOG-specific Th17 cells, but not Th17-activated CTLs induced EAE in C57BL/6 mice. Taken together, our data indicate a distinct role of Th17 cells and Th17-stimulated CTLs in the pathogenesis of TID and EAE, which may have great impact on the overall understanding of Th17 cells in the pathogenesis of autoimmune diseases.

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.

Relevance of IL7R genotype and mRNA expression in Dutch patients with multiple sclerosis

Background: The interleukin 7 receptor (IL7R) has been recognized as a susceptibility gene for Multiple Sclerosis (MS). Analysis of rs6897932 (the most strongly MS-associated single nucleotide polymorphism (SNP)), showed effects of genotype on the relative expression of membrane-bound to total amount of IL7R mRNA.

Objective: We assessed the relevance of IL7R on MS phenotype (including clinical and magnetic resonance imaging (MRI) parameters) at DNA and mRNA level in Dutch patients with MS.

Methods: The genotype of rs6897932 was analyzed in 697 patients with MS and 174 healthy controls. The relevance of genotype and carriership of the C allele on MS phenotype (disease activity and severity, using clinical and MRI parameters) was assessed. In addition, relative gene expression of membrane-bound to total IL7R mRNA was analyzed with respect to disease phenotype in a subgroup of 95 patients with early relapsing MS.

Results: In particular, homozygosity for the risk allele is a risk factor for MS in our population (ORCC vs CT and TT = 1.65 (95% CI: 1.18–2.30), two-sided p = 0.004). However, no effect of genotype or the relative expression of membrane-bound IL7R (presence of exon 6–7) to total amount of IL7R mRNA (presence of exon 4–5) was found on MS phenotype.

Discussion: Homozygosity for the IL7R exon 6 rs6897932 C allele is associated with a higher risk for MS in our Dutch population. No effect was found of genotype or mRNA expression on disease phenotype.

Therapies for multiple sclerosis: considerations in the pediatric patient

Current and emerging therapies for multiple sclerosis (MS) offer promise for improved disease control and long-term clinical outcome. To date, these therapies have been evaluated solely in the context of adult MS. However, onset of MS in children is being increasingly recognized, and recent studies have identified a significant impact of MS onset during childhood on cognitive and physical functioning. Optimization of pediatric MS care requires that promising new therapies be made available to children and adolescents, but also that safety and tolerability and potential influence of therapies on the developing immune and neural networks of pediatric patients be closely considered. We propose care algorithms illustrating models for therapy that detail careful monitoring of pediatric patients with MS, provide definitions for inadequate treatment response and treatment escalation, and foster multinational collaboration in future therapeutic trials.

HLA-DPB1 0501 is associated with susceptibility to anti-aquaporin-4 antibodies positive neuromyelitis optica in southern Han Chinese

OBJECTIVES

To analyze the role of HLA-DRB1 and -DPB1 alleles in the pathogenesis of neuromyelitis optica (NMO) and multiple sclerosis in Southern Han Chinese.

METHODS

Thirty serum anti-aquaporin 4 antibodies (AQP4-Ab)-positive NMO patients, 53 conventional multiple sclerosis (C-MS) patients, and 93 controls (CTLs) were enrolled. The HLA-DRB1 and -DPB1 alleles of the subjects were determined by sequencing-based typing (SBT).

RESULTS

The frequency of the DRB1 0901 was lower in NMO patients than in CTLs (P(uncorr)=0.022, OR: 0.194, 95% CI: 0.043-0.876), and DRB1 1602 was higher in NMO patients than in C-MS (P(uncorr)=0.038, OR: 3.491, 95% CI: 1.024-11.896) and CTLs (P(uncorr)=0.051, OR: 2.711, 95% CI: 0.971-7.556). The frequency of DPB1 0501 was significant higher in NMO patients than in C-MS (P(uncorr)=0.018, OR: 4.629, 95% CI: 1.235-17.350) and CTLs (P(uncorr)=0.001, P(corr)=0.022, OR: 7.096, 95% CI: 2.011-25.044).

CONCLUSIONS

DPB1 0501 correlates with risk of AQP4-Ab positive NMO in Southern Han Chinese.

Association of single-nucleotide polymorphisms in FOXP3 gene with systemic lupus erythematosus susceptibility: a case-control study

Foxp3, encoded by the human FOXP3 gene, is a transcription factor that regulates regulatory T-cell (Treg) development and function. Associations have been reported between FOXP3 gene variants and autoimmune endocrinopathy and non-endocrine autoimmune disease. The aim of this study was to investigate the possible influence of single nucleotide polymorphisms (SNP) in the FOXP3 gene on genetic predisposition to systemic lupus erythematosus (SLE). The study cohort comprised 172 SLE patients and 181 controls, who were genotyped for the FOXP3 gene variants. Of five SNPs identified, the FOXP3 -6054 ATT carrier was shown to be associated with renal disorder (odds ratio [OR] 3.26, 95% confidence interval [95% CI] 1.33-8.03, p = 0.0077). Furthermore, lower anti-dsDNA levels were found in patients with the -3279 A carrier (p = 0.0109). To the authors' knowledge, this is the first study to investigate the association of FOXP3 SNPs with susceptibility to SLE, as well as sub-phenotype susceptibility. Although the exact role of Foxp3 and FOXP3 gene variations in SLE is still not clear, the present data support the importance of variations in the FOXP3 gene region for the etiology of certain manifestations of SLE.

Dysregulation of thymic clonal deletion and the escape of autoreactive T cells

Events ongoing in the thymus are critical for deleting developing thymocytes specific for tissue antigens, and establishing self-tolerance within the T cell compartment. Aberrant thymic negative selection, however, is believed to generate a repertoire with increased self-reactivity, which in turn can contribute to the development of T cell-mediated autoimmunity. In this review, mechanisms that regulate the efficacy of negative selection and influence the deletion of autoreactive thymocytes will be discussed.

Translational research in neurology and neuroscience 2010: multiple sclerosis

Over the past 2 decades, enormous progress has been made with regard to pharmacotherapies for patients with multiple sclerosis. There is perhaps no other subspecialty in neurology in which more agents have been approved that substantially alter the clinical course of a disabling disorder. Many of the pharmaceuticals that are currently approved, in clinical trials, or in preclinical development were initially evaluated in an animal model of multiple sclerosis, experimental autoimmune encephalomyelitis. Two Food and Drug Administration-approved agents (glatiramer acetate and natalizumab) were developed using the experimental autoimmune encephalomyelitis model. This model has served clinician-scientists for many decades to enable understanding the inflammatory cascade that underlies clinical disease activity and disease surrogate markers detected in patients.

Genome-wide screening for risk loci of idiopathic recurrent miscarriage in a Han Chinese population: a pilot study

The etiology of recurrent miscarriage (RM) is extremely heterogeneous, including genetic, immunologic, anatomic, endocrinological, and infectious anomalies. About 50% of RM is unexplained or poorly understood, which is called idiopathic recurrent miscarriage (IRM). The primary aim of this study was to identify the genetic loci that might be susceptible to IRM. Forty-four Han Chinese patients with IRM during the first trimester of their pregnancies and 44 healthy sex- and ethnic-matched controls were enrolled in this study. A case-control and genome-wide study was performed and 430 polymorphic microsatellite markers were analyzed. Three loci, 6q27 (D6S446, P = .028), 9q33.1 (D9S1776, P = .037), and Xp22.11 (DXS1226, P = .008), significantly associated with IRM were found. This work identified 3 genetic regions that might harbor genes predisposed to IRM and provided new insights for future genetic and etiological study of IRM. Further study is required to confirm it.

The effect of single nucleotide polymorphisms from genome wide association studies in multiple sclerosis on gene expression

Background

Multiple sclerosis (MS) is a complex neurological disorder. Its aetiology involves both environmental and genetic factors. Recent genome-wide association studies have identified a number of single nucleotide polymorphisms (SNPs) associated with susceptibility to (MS). We investigated whether these genetic variations were associated with alteration in gene expression.

Methods/Principal Findings

We used a database of mRNA expression and genetic variation derived from immortalised peripheral lymphocytes to investigate polymorphisms associated with MS for correlation with gene expression. Several SNPs were found to be associated with changes in expression: in particular two with HLA-DQA1, HLA-DQA2, HLA-DQB1, HLA-DRB1, HLA-DRB4 and HLA-DRB5, one with ZFP57, one with CD58, two with IL7 and FAM164A, and one with FAM119B, TSFM and KUB3. We found minimal cross-over with a recent whole genome expression study in MS patients.

Discussion

We have shown that many susceptibility loci in MS are associated with changes in gene expression using an unbiased expression database. Several of these findings suggest novel gene candidates underlying the effects of MS-associated genetic variation.

CIITA variation in the presence of HLA-DRB1*1501 increases risk for multiple sclerosis

The MHC class II transactivator gene (CIITA) is an important transcription factor regulating gene required for HLA class II MHC-restricted antigen presentation. Association with HLA class II variation, particularly HLA-DRB1*1501, has been well-established for multiple sclerosis (MS). In addition, the -168A/G CIITA promoter variant (rs3087456) has been reported to be associated with MS. Thus, a multi-stage investigation of variation within CIITA, DRB1*1501 and MS was undertaken in 6108 individuals. In stage 1, 24 SNPs within CIITA were genotyped in 1320 cases and 1363 controls (n = 2683). Rs4774 (missense +1614G/C; G500A) was associated with MS (P = 4.9 x 10(-3)), particularly in DRB1*1501 +individuals (P = 1 x 10(-4)). No association was observed for the -168A/G promoter variant. In stage 2, rs4774 was genotyped in 973 extended families; rs4774*C was also associated with increased risk for MS in DRB1*1501+ families (P = 2.3 x 10(-2)). In a third analysis, rs4774 was tested in cases and controls (stage 1) combined with one case per family (stage 2) for increased power. Rs4774*C was associated with MS (P = 1 x 10(-3)), particularly in DRB1*1501+ cases and controls (P = 1 x 10(-4)). Results obtained from logistic regression analysis showed evidence for interaction between rs4774*C and DRB1*1501 associated with risk for MS (ratio of ORs = 1.72, 95% CI 1.28-2.32, P = 3 x 10(-4)). Furthermore, rs4774*C was associated with DRB1*1501+ MS when conditioned on the presence (OR = 1.67, 95% CI = 1.19-2.37, P = 1.9 x 10(-3)) and absence (OR = 1.49, 95% CI = 1.15-1.95, P = 2.3 x 10(-3)) of CLEC16A rs6498169*G, a putative MS risk allele adjacent to CIITA. Our results provide strong evidence supporting a role for CIITA variation in MS risk, which appears to depend on the presence of DRB1*1501.

Latitudinal variation in incidence and type of first central nervous system demyelinating events

Increasing prevalence and variable geographic patterns of occurrence of multiple sclerosis suggest an environmental role in causation. There are few descriptive, population-level, data on whether such variability applies to first demyelinating events (FDEs). We recruited 216 adults (18-59 years), with a FDE between 1 November 2003 and 31 December 2006 in a multi-center incident case-control study in four locations on the south-eastern and eastern seaboard of Australia, spanning latitudes 27 degrees south to 43 degrees south. Population denominators were obtained from the Australian Bureau of Statistics censuses of 2001 and 2006. Age and sex adjusted FDE incidence rates increased by 9.55% (95% confidence interval (CI) 7.37-11.78, p < 0.001) per higher degree of latitude. The incidence rate gradient per higher degree of latitude varied by gender (male: 14.69% (95% CI 9.68-19.94, p < 0.001); female 8.13% (95% CI 5.69-10.62, p < 0.001)); and also by the presenting FDE type: optic neuritis 11.39% (95% CI 7.15-15.80, p < 0.001); brainstem/cerebellar syndrome 9.47% (95% CI 5.18-13.93, p < 0.001); and spinal cord syndrome 5.36% (95% CI 1.78-9.06, p = 0.003). Differences in incidence rate gradients were statistically significant between males and females (p = 0.02) and between optic neuritis and spinal cord syndrome (p = 0.04). The male to female ratio varied from 1 : 6.7 at 27 degrees south to 1 : 2.5 at 43 degrees south. The study establishes a positive latitudinal gradient of FDE incidence in Australia. The latitude-related factor(s) influences FDE incidence variably according to subtype and gender, with the strongest influence on optic neuritis presentations and for males. These descriptive case analyses show intriguing patterns that could be important for understanding the etiology of multiple sclerosis.

Genetic variation in the IL7RA/IL7 pathway increases multiple sclerosis susceptibility

Multiple sclerosis (MS) is characterized as an autoimmune demyelinating disease. Numerous family studies have confirmed a strong genetic component underlying its etiology. After several decades of frustrating research, the advent and application of affordable genotyping of dense SNP maps in large data sets has ushered in a new era in which rapid progress is being made in our understanding of the genetics underlying many complex traits. For MS, one of the first discoveries to emerge in this new era was the association with rs6897932[T244I] in the interleukin-7 receptor alpha chain (IL7RA) gene (Gregory et al. in Nat Genet 39(9):1083-1091, 2007; International Multiple Sclerosis Genetics Consortium in N Engl J Med 357(9):851-862, 2007; Lundmark in Nat Genet 39(9):1108-1113, 2007), a discovery that was accompanied by functional data that suggest this variant is likely to be causative rather than a surrogate proxy (Gregory et al. in Nat Genet 39(9):1083-1091, 2007). We hypothesized that variations in other genes functionally related to IL7RA might also influence MS. We investigated this hypothesis by examining genes in the extended biological pathway related to IL7RA to identify novel associations. We identified 73 genes with putative functional relationships to IL7RA and subsequently genotyped 7,865 SNPs in and around these genes using an Illumina Infinium BeadChip assay. Using 2,961 case-control data sets, two of the gene regions examined, IL7 and SOCS1, had significantly associated single-nucleotide polymorphisms (SNPs) that further replicated in an independent case-control data set (4,831 samples) with joint p values as high as 8.29 x 10(-6) and 3.48 x 10(-7), respectively, exceeding the threshold for experiment-wise significance. Our results also implicate two additional novel gene regions that are likely to be associated with MS: PRKCE with p values reaching 3.47 x 10(-4), and BCL2 with p values reaching 4.32 x 10(-4). The TYK2 gene, which also emerged in our analysis, has recently been associated with MS (Ban et al. 2009). These results help to further delineate the genetic architecture of MS and validate our pathway approach as an effective method to identify novel associations in a complex disease.

Haplotype 4 of the multiple sclerosis-associated interleukin-7 receptor alpha gene influences the frequency of recent thymic emigrants

The receptor for the homeostatic T cell cytokine interleukin-7 (IL-7Ralpha) has recently shown genetic association to multiple sclerosis (MS). To investigate the functional contribution of IL-7Ralpha polymorphisms to the pathogenesis of MS, we correlated the IL-7Ralpha haplotypes with different T cell parameters in a group of MS patients and healthy controls. We show that carriers of one of the four IL-7Ralpha haplotypes (Hap4) show a higher expression of IL-7Ralpha (CD127) on their CD4(+) T cells, compared with noncarriers (P=0.04). Moreover, Hap4 carriers possess higher frequencies of recent thymic emigrants (RTEs, CD31(+)) in both the regulatory T cell (Treg; P=0.007) and conventional T cell (Tconv) population (P=0.0001). This effect is most pronounced within the MS population (Treg, P=0.0077; Tconv, P=0.0007), whereas in healthy controls significance was only reached for Tconv (P=0.043; Treg, P=0.11). Because previous studies showed a decreased RTE-Treg frequency in MS patients compared to healthy subjects, we here conclude that this decrease is localized within the MS population of non-Hap4 carriers. In conclusion, our findings suggest that IL-7Ralpha polymorphisms can influence T cell development and homeostasis, and thereby contribute to the altered immune regulation associated with disease development in patients with MS.

Prevention and treatment of experimental autoimmune encephalomyelitis with clonotypic CDR3 peptides: CD4(+) Foxp3(+) T-regulatory cells suppress interleukin-2-dependent expansion of myelin basic protein-specific T cells

T-cell receptor (TCR)-derived peptides are recognized by the immune system and are capable of modulating autoimmune responses. Using the myelin basic protein (MBP) TCR 1501 transgenic mouse model, we demonstrated that TCR CDR3 peptides from the transgenic TCR can provide a protective effect when therapy is initiated before the induction of experimental autoimmune encephalomyelitis (EAE). More importantly, TCR CDR3 peptide therapy can ameliorate the disease when administered after EAE onset. Concurrent with the therapeutic effects, we observed reduced T-cell proliferation and reduced interleukin-2 (IL-2) levels in response to stimulation with MBP-85-99 peptide in splenocyte cultures from mice receiving TCR CDR3 peptides compared with that of control mice. Moreover, we found that Foxp3(+) CD4 T cells from mice protected with TCR CDR3 peptide are preferentially expanded in the presence of IL-2. This is supportive of a proposed mechanism where Foxp3(+) T-regulatory cells induced by therapy with MBP-85-99 TCR CDR3 peptides limit expansion and the encephalitogenic activity of MBP-85-99-specific T cells by regulating the levels of secreted IL-2.

European Charcot Foundation Lecture: the natural history of multiple sclerosis and gender

The role of gender in the natural history of multiple sclerosis (MS) is multi-faceted. Earliest debate on this topic was about the sex ratio (female:male) among affected individuals. It was only clearly shown within the last 4 decades that females are more often affected. The sex ratio continues to intrigue researchers. An observed increase in the sex ratio among more recently born MS patients has now been taken as a clear indication that the rate of MS is truly increasing in many geographical areas. This temporal increase in females has been relatively rapid, implicating environmental rather than genetic risk factors. Gender issues in MS expand beyond the scope of sex ratio. Gender has an impact on various aspects of MS, including age of onset, "parent-of-origin" effects (seen in half-siblings, twin sibships, avuncular pairs, transmission of HLA haplotype), recurrence risks for relatives of MS patients and the topic of reproduction when one parent has MS. Gender issues can also confound data collection and analyses with respect to studies on comorbidity, risk factors and family history. In fact, it has now been clearly validated and quantified that among persons with MS, there is a sex-specificity of recall and reporting bias as well a greater female awareness of medical history.

Genetics and pathogenesis of multiple sclerosis

Multiple sclerosis (MS) is an idiopathic autoimmune neurodegenerative disease. Like many common diseases, MS has a genetic component; however, as with most complex diseases, the genetic architecture may be influenced by heterogeneity, incomplete penetrance, polygenic inheritance, and environmental factors. This clinically complex disease has provided great challenges for geneticists over the years. Although the first consistent genetic association to MS (with HLA-DR*1501) was discovered more than 30 years ago, lack of consistently replicated genetic results has plagued the scientific community. New study design methods (particularly genome-wide associations studies [GWAS]) along with genome project data and larger datasets have allowed several additional MS genes to be identified and consistently replicated. Thus, after many years of frustration, the strong genetic component associated with MS is finally beginning to be characterized.

Variation in IL7R predisposes to sarcoid inflammation

Sarcoidosis is a chronic granulomatous disorder characterized by a massive influx of Th1 lymphocytes. Both naive and memory T cells express high levels of interleukin 7 receptor-alpha (IL7R alpha), encoded by the IL7R gene. The purpose of this study was to investigate the role of the IL7R gene region in susceptibility to sarcoidosis. Six common single-nucleotide polymorphisms (SNPs) spanning IL7R were genotyped and analyzed in 475 sarcoidosis patients and 465 healthy controls. Replication of one significant associated SNP was carried out in 206 independent sarcoidosis patients, 127 controls and 126 patients with Löfgren's disease. The rs10213865 SNP was associated with sarcoidosis (P=0.008), and in silico analysis showed a complete linkage (r(2)=1, D'=1) with a functional nonsynonymous coding SNP in exon 6 (rs6897932, T244I). Combined analysis of 663 individuals with sarcoidosis and 586 controls (homozygous carriers of risk allele, P=5 x 10(-4), odds ratio=1.49 (1.19-1.86)) provided strong statistical support for a genuine association of IL7R with the risk of sarcoidosis. In addition, we report the same trend between variation in the IL7R gene and patients with Löfgren's disease, suggesting that variation in IL7R may confer general risk for developing granulomatous lung disease.

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.

Association studies of the SAS-ZFAT, IL-23R, IFIH1 and FOXP3 genes in autoimmune thyroid disease

Autoimmune thyroid diseases (AITDs) are complex diseases caused by an interaction between susceptibility genes and environmental triggers. Genetic susceptibility in combination with external factors, such as dietary iodine, is believed to initiate the autoimmune response against thyroid antigens. Abundant epidemiological data, including family and twin studies, point to a strong genetic influence in the development of AITDs. Various techniques have been employed to identify genes contributing to the etiology of AITDs, including candidate gene analysis and whole-genome screening. These studies have enabled the identification of several loci (genetic regions) that are linked to AITDs and, in some of these loci, putative AITD-susceptibility genes have been identified. Some of these genes/loci are unique to Graves' disease (GD) and Hashimoto's thyroiditis (HT), and some are common to both diseases, indicating that there is a shared genetic susceptibility to GD and HT. The putative GD and HT susceptibility genes include both immune-modifying genes (e.g., HLA, CTLA-4 and PTPN22) and thyroid-specific genes (e.g., TSHR and Tg). In this special report, we focus on the newest genes identified and not on those previously identified, such as HLA and CTLA-4, for which there are many reviews.

Epistasis among HLA-DRB1, HLA-DQA1, and HLA-DQB1 loci determines multiple sclerosis susceptibility

Multiple sclerosis (MS), a common central nervous system inflammatory disease, has a major heritable component. Susceptibility is associated with the MHC class II region, especially HLA-DRB5*0101-HLA-DRB1*1501-HLA-DQA1*0102-HLA-DQB1*0602 haplotypes(hereafter DR2), which dominate genetic contribution to MS risk. Marked linkage disequilibrium (LD) among these loci makes identification of a specific locus difficult. The once-leading candidate, HLA-DRB1*15, localizes to risk, neutral, and protective haplotypes. HLA-DRB1*15 and HLA-DQB1*0602, nearly always located together on a small ancestral chromosome segment, are strongly MS-associated. One intervening allele on this haplotype, viz. HLA-DQA1*0102, shows no primary MS association. Two Canadian cohorts (n = 830 and n = 438 trios) genotyped for HLA-DRB1, HLA-DQA1 and HLA-DQB1 alleles were tested for association using TDT. To evaluate epistasis involving HLA-DRB1*15, transmissions from HLA-DRB1*15-negative parents were stratified by the presence/absence of HLA-DRB1*15 in affected offspring. All 3 alleles contribute to MS susceptibility through novel epistatic interactions. HLA-DQA1*0102 increased disease risk when combined with HLA-DRB1*1501 in trans, thereby unambiguously implicating HLA-DQ in MS susceptibility. Three-locus haplotypes demonstrated that HLA-DRB1*1501 and HLA-DQB1*0602 each influence risk. Transmissions of rare morcellated DR2 haplotypes showed no interaction with HLA-DQA1*0102. Incomplete haplotypes bearing only HLA-DRB1*1501 or HLA-DQB1*0602 did not predispose to MS. Balanced reciprocal transmission distortion can mask epistatic allelic association. These findings implicate epistasis among HLA class II alleles in human immune responses generally, provide partial explanation for intense linkage disequilibrium in the MHC, have relevance to animal models, and demonstrate key roles for DR2-specific interactions in MS susceptibility. MHC disease associations may be more generally haplotypic or diplotypic.

A follow-up study of chromosome 19q13 in multiple sclerosis susceptibility

A possible role of allelic variation on chromosome 19q13 in multiple sclerosis (MS) susceptibility has been suggested. We tested association of sixteen 19q13 markers with MS in 459 families. Nominally significant associations were tested in an independent set of 323 families as well as in the pooled set of 782 families. We were not able to confirm previously suggested associations with APOE, GIPR, ZNF45, ILT6 and D19S585. In the screening dataset nominally significant associations were found with D19S867 and with APOE haplotype (p=0.007 in both), but these were not replicated in the independent dataset nor in the pooled analysis of 757 families. Thus, we were not able to detect any statistically significant allelic associations. Re-sequencing based approaches may be required for elucidating the role chromosome 19q13 with MS.

Pathway and network-based analysis of genome-wide association studies in multiple sclerosis

Genome-wide association studies (GWAS) testing several hundred thousand SNPs have been performed in multiple sclerosis (MS) and other complex diseases. Typically, the number of markers in which the evidence for association exceeds the genome-wide significance threshold is very small, and markers that do not exceed this threshold are generally neglected. Classical statistical analysis of these datasets in MS revealed genes with known immunological functions. However, many of the markers showing modest association may represent false negatives. We hypothesize that certain combinations of genes flagged by these markers can be identified if they belong to a common biological pathway. Here we conduct a pathway-oriented analysis of two GWAS in MS that takes into account all SNPs with nominal evidence of association (P < 0.05). Gene-wise P-values were superimposed on a human protein interaction network and searches were conducted to identify sub-networks containing a higher proportion of genes associated with MS than expected by chance. These sub-networks, and others generated at random as a control, were categorized for membership of biological pathways. GWAS from eight other diseases were analyzed to assess the specificity of the pathways identified. In the MS datasets, we identified sub-networks of genes from several immunological pathways including cell adhesion, communication and signaling. Remarkably, neural pathways, namely axon-guidance and synaptic potentiation, were also over-represented in MS. In addition to the immunological pathways previously identified, we report here for the first time the potential involvement of neural pathways in MS susceptibility.

Disease-modifying agents for multiple sclerosis: recent advances and future prospects

Multiple sclerosis (MS) is a chronic autoimmune disease of the CNS. Currently, six medications are approved for immunmodulatory and immunosuppressive treatment of the relapsing disease course and secondary-progressive MS. In the first part of this review, the pathogenesis of MS and its current treatment options are discussed. During the last decade, our understanding of autoimmunity and the pathogenesis of MS has advanced substantially. This has led to the development of a number of compounds, several of which are currently undergoing clinical testing in phase II and III studies. While current treatment options are only available for parenteral administration, several oral compounds are now in clinical trials, including the immunosuppressive agents cladribine and laquinimod. A novel mode of action has been described for fingolimod, another orally available agent, which inhibits egress of activated lymphocytes from draining lymph nodes. Dimethylfumarate exhibits immunomodulatory as well as immunosuppressive activity when given orally. All of these compounds have successfully shown efficacy, at least in regards to the surrogate marker contrast-enhancing lesions on magnetic resonance imaging. Another class of agents that is highlighted in this review are biological agents, namely monoclonal antibodies (mAb) and recombinant fusion proteins. The humanized mAb daclizumab inhibits T-lymphocyte activation via blockade of the interleukin-2 receptor. Alemtuzumab and rituximab deplete leukocytes and B cells, respectively; the fusion protein atacicept inhibits specific B-cell growth factors resulting in reductions in B-cells and plasma cells. These compounds are currently being tested in phase II and III studies in patients with relapsing MS. The concept of neuro-protection and -regeneration has not advanced to a level where specific compounds have entered clinical testing. However, several agents approved for conditions other than MS are highlighted. Finally, with the advent of these highly potent novel therapies, rare, but potentially serious adverse effects have been noted, namely infections and malignancies. These are critically reviewed and put into perspective.

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.

Gene-environment interactions between HLA B7/A2, EBV antibodies are associated with MRI injury in multiple sclerosis

PURPOSE

To determine the role of gene-environmental interactions between the Class I and Class II HLA alleles and the humoral anti-Epstein-Barr Virus (EBV) responses in the development of brain injury and clinical disability in multiple sclerosis (MS) patients.

METHODS

A total of 93 MS patients (62 females; 31 males) and 122 healthy controls underwent HLA typing and testing for antibodies against EBV. The MS patients underwent brain MRI and quantitative measurements of T1- and T2-lesion volumes (LVs) and brain parenchymal fraction (BPF) were obtained. There were 54 MS cases that underwent MRI and EBV-antibody assessments at the 3-year follow-up. The anti-EBV panel included measurements of the levels of anti-EBV early antigen (EA) IgG, anti-EBV nuclear antigen (EBNA) IgG and anti-EBV viral capsid antigen (VCA) IgM and anti-EBV VCA IgG. The relationships between HLA alleles, anti-EBV antibody levels, MRI and clinical parameters were assessed in regression analysis.

RESULTS

The presence of HLA B7 was associated with increased T1-LV and trends indicating increased anti-EBV VCA IgG levels, higher disability (EDSS) and more destructive MRI parameters (increased T2-LV and decreased BPF). The presence of HLA A2 was associated with lower EDSS and a trend toward decreased anti-EBV VCA IgG levels; the associations with MRI variables were not significant. The HLA B7-A2 haplotype was significantly associated with higher T2-LV and T1-LV and a trend toward lower BPF was observed.

CONCLUSIONS

Our data suggest that gene-environment interactions between specific HLA Class I loci and EBV exposure are associated with MRI markers of lesion injury and brain atrophy in MS patients.

Complement in multiple sclerosis: its role in disease and potential as a biomarker

Multiple sclerosis (MS) is a common inflammatory disease of the central nervous system with a poorly defined and complex immunopathogenesis. Although initiated by reactive T cells, persistent inflammation is evident throughout the disease course. A contribution from complement has long been suspected, based on the results of pathological and functional studies which have demonstrated complement activation products in MS brain and biological fluids. However, the extent and nature of complement activation and its contribution to disease phenotype and long-term outcome remain unclear. Furthermore, functional polymorphisms in components and regulators of the complement system which cause dysregulation, and are known to contribute to other autoimmune inflammatory disorders, have not been investigated to date in MS in any detail. In this paper we review evidence from pathological, animal model and human functional and genetic studies, implicating activation of complement in MS. We also evaluate the potential of complement components and regulators and their polymorphic variants as biomarkers of disease, and suggest appropriate directions for future research.

Genotype-Phenotype correlations in multiple sclerosis: HLA genes influence disease severity inferred by 1HMR spectroscopy and MRI measures

Genetic susceptibility to multiple sclerosis (MS) is associated with the human leukocyte antigen (HLA) DRB1*1501 allele. Here we show a clear association between DRB1*1501 carrier status and four domains of disease severity in an investigation of genotype-phenotype associations in 505 robust, clinically well characterized MS patients evaluated cross-sectionally: (i) a reduction in the N-acetyl-aspartate (NAA) concentration within normal appearing white matter (NAWM) via (1)HMR spectroscopy (P = 0.025), (ii) an increase in the volume of white matter (WM) lesions utilizing conventional anatomical MRI techniques (1,127 mm(3); P = 0.031), (iii) a reduction in normalized brain parenchymal volume (nBPV) (P = 0.023), and (iv) impairments in cognitive function as measured by the Paced Auditory Serial Addition Test (PASAT-3) performance (Mean Z Score: DRB1*1501+: 0.110 versus DRB1*1501-: 0.048; P = 0.004). In addition, DRB1*1501+ patients had significantly more women (74% versus 63%; P = 0.009) and a younger mean age at disease onset (32.4 years versus 34.3 years; P = 0.025). Our findings suggest that DRB1*1501 increases disease severity in MS by facilitating the development of more T2-foci, thereby increasing the potential for irreversible axonal compromise and subsequent neuronal degeneration, as suggested by the reduction of NAA concentrations in NAWM, ultimately leading to a decline in brain volume. These structural aberrations may explain the significant differences in cognitive performance observed between DRB1*1501 groups. The overall goal of a deep phenotypic approach to MS is to develop an array of meaningful biomarkers to monitor the course of the disease, predict future disease behaviour, determine when treatment is necessary, and perhaps to more effectively recommend an available therapeutic intervention.

No evidence for shared etiology in two demyelinative disorders, MS and PLOSL

Loss-of-function mutations of DAP12 and TREM2 cause a recessively inherited disease PLOSL, manifesting in brain white matter. The genes of the DAP12-TREM2 signaling receptor are located on 19q13.12 and 6p21.1, to which linkage has been observed also in families affected by another immune-mediated demyelinating disease, MS. We have tested if allelic variation in DAP12 or TREM2 predisposes also to MS by monitoring carrier frequency of the Finnish PLOSL mutation in Finnish MS cases and by studying DAP12 and TREM2 in MS by linkage and association. To conclude, the DAP12-TREM2 complex unlikely has a role in genetic susceptibility of MS.

The T244I variant of the interleukin-7 receptor-alpha gene and multiple sclerosis

Several but not all studies have provided evidence for the association between multiple sclerosis (MS) and the T244I variant of the interleukin-7 receptor-alpha gene (IL7RA), rs6897932. We performed a new replication case-control study in 599 MS patients and 594 healthy controls, all Caucasians from the south of Spain. The genotype and allele frequencies differed between MS cases and controls. The IL7RA rs6897932 C allele and the CC genotype were found to be factors for disease susceptibility [per allele odds ratio (OR) 1.32, 95% CI 1.1-1.6, P=0.0031; per CC genotype vs TT + TC genotypes, OR 1.5, 95% CI 1.18-1.87, P=0.0007]. The combined data analysis included 3324 cases and 5032 controls of Europeans and Americans of European origin resulting in stronger association with similar OR (P=1.9 x 10E-9). These findings in our sample support previous reported association studies between IL7RA rs6897932 and 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.

Myelin-reactive type B T cells and T cells specific for low-affinity MHC-binding myelin peptides escape tolerance in HLA-DR transgenic mice

Genes of the MHC show the strongest genetic association with multiple sclerosis (MS), but the underlying mechanisms have remained unresolved. In this study, we asked whether the MS-associated MHC class II molecules, HLA-DRB1*1501, HLA-DRB5*0101, and HLA-DRB1*0401, contribute to autoimmune CNS demyelination by promoting pathogenic T cell responses to human myelin basic protein (hMBP), using three transgenic (Tg) mouse lines expressing these MHC molecules. Unexpectedly, profound T cell tolerance to the high-affinity MHC-binding hMBP82-100 epitope was observed in all Tg mouse lines. T cell tolerance to hMBP82-100 was abolished upon back-crossing the HLA-DR Tg mice to MBP-deficient mice. In contrast, T cell tolerance was incomplete for low-affinity MHC-binding hMBP epitopes. Furthermore, hMBP82-100-specific type B T cells escaped tolerance in HLA-DRB5*0101 Tg mice. Importantly, T cells specific for low-affinity MHC-binding hMBP epitopes and hMBP82-100-specific type B T cells were highly encephalitogenic. Collectively, the results show that MS-associated MHC class II molecules are highly efficient at inducing T cell tolerance to high-affinity MHC-binding epitope, whereas autoreactive T cells specific for the low-affinity MHC-binding epitopes and type B T cells can escape the induction of T cell tolerance and may promote MS.

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.

Multiple Sclerosis disease distribution and potential impact of environmental air pollutants in Georgia

Multiple Sclerosis (MS) is one of the most common diseases of the central nervous system. Although the disease has been associated with some genetic and environmental factors, it has neither clear causes nor clear temporality with respect to exposure. The purpose of this study was to explore potential relationships between MS and outdoor air pollutants in GA. This study used cross-sectional data from the member's list of the Multiple Sclerosis Society's GA chapter (MSS-GA), the US Census, and a database of county-level Toxic Release Inventory data (emissions across identified, reporting sources to outdoor air, as a surrogate indicator of potential exposure to a criteria pollutant subject to regulation or to chemical toxicants). The final study population was 9,072,576 people, including 6247 self-reported MS cases from MSS-GA. Cases were stratified by gender and transformed into county-level, self-reported prevalence rates using 2005 US Census estimates. County-level prevalence was displayed using a Geographic Information System. Linear regression was conducted to investigate potential relationships between self-reported MS prevalence rates, census data, and environmental outdoor air pollutant indicators. MS prevalence tended to be clustered within the largest metropolitan statistical area (MSA) in Georgia, around Atlanta (Fulton County). The best predictive models for the MS prevalence in GA included both per capita income and PM-10 for females, but only per capita income only for males. The clustering of prevalence of MS in the largest MSA of Georgia, after controlling for population distribution, suggested that urban attributes may be associated with MS. The results of this study further suggested a potential role of PM-10 in the etiology of MS in females, perhaps due to the influence of PM-10 on systemic immune response and inflammation. Based on this initial exploratory study, we recommend more basic and clinical exposure research to understand environmental influences on MS. In particular, outdoor air pollutants like particles, and attached chemicals and metals, which have other known adverse cardiopulmonary health outcomes and are subject to federal and state regulations, could be examined using routinely collected outdoor air monitoring station data and/or modeling.

A first stage genome-wide screen for regions shared identical-by-descent in Hutterite families with multiple sclerosis

The complexity of multiple sclerosis (MS) genetics has made the search for novel genes using traditional sharing methods problematic. In order to minimize the genetic heterogeneity present in the MS population we have screened the Canadian MS population for individuals belonging to the Hutterite Brethren. Seven Hutterites with clinically definite MS were ascertained and are related to a common founder by eight generations. Six of the 7 affected individuals and 21 of their unaffected family members (total = 27) were genotyped for 807 markers. Haplotypes were then inspected for sharing among the six MS patients. There were three haplotypes shared among all six MS patients. The haplotypes were located at 2q34-35, 4q31-32, and 17p13. An additional 15 haplotypes were shared among five of the six Hutterites MS patients. The HLA Class II region was one of the highlighted regions; however, the shared MHC haplotype bore the DRB1*04 allele and not the MS-associated DRB1*15 allele providing further evidence of the complexity of the MHC. Additional genotyping to refine the haplotypes followed by screening for potential variants may lead to the identification of a novel MS susceptibility gene(s) in this unique population.

Genetic Factors and Orofacial Clefting

Cleft lip with or without cleft palate is the most common facial birth defect and it is caused by a complex interaction between genetic and environmental factors. The purpose of this review is to provide an overview of the spectrum of the genetic causes for cleft lip and cleft palate using both syndromic and nonsyndromic forms of clefting as examples. Although the gene identification process for orofacial clefting in humans is in the early stages, the pace is rapidly accelerating. Recently, several genes have been identified that have a combined role in up to 20% of all clefts. While this is a significant step forward, it is apparent that additional cleft causing genes have yet to be identified. Ongoing human genome-wide linkage studies have identified regions in the genome that likely contain genes that when mutated cause orofacial clefting, including a major gene on chromosome 9 that is positive in multiple racial groups. Currently, efforts are focused to identify which genes are mutated in these regions. In addition, parallel studies are also evaluating genes involved in environmental pathways. Furthermore, statistical geneticists are developing new methods to characterize both gene-gene and gene-environment interactions to build better models for pathogenesis of this common birth defect. The ultimate goal of these studies is to provide knowledge for more accurate risk counseling and the development of preventive therapies.

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.

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.

Finding disease candidate genes by liquid association

A novel approach to finding candidate genes by using gene-expression data has been developed and used to identify a multiple sclerosis susceptibility candidate genes.

A novel approach to finding candidate genes by using gene expression data through liquid association is developed and used to identify multiple sclerosis susceptibility candidate genes.