Shared Genetic Risk Factors for Multiple Sclerosis/Psoriasis Suggest Involvement of Interleukin-17 and Janus Kinase-Signal Transducers and Activators of Transcription Signaling.

OBJECTIVE: Psoriasis and multiple sclerosis (MS) are complex immune diseases that are mediated by T cells and share multiple comorbidities. Previous studies have suggested psoriatic patients are at higher risk of MS; however, causal relationships between the two conditions remain unclear. Through epidemiology and genetics, we provide a comprehensive understanding of the relationship, and share molecular factors between psoriasis and MS. METHODS: We used logistic regression, trans-disease meta-analysis and Mendelian randomization. Medical claims data were included from 30 million patients, including 141,544 with MS and 742,919 with psoriasis. We used genome-wide association study summary statistics from 11,024 psoriatic, 14,802 MS cases, and 43,039 controls for trans-disease meta-analysis, with additional summary statistics from 5 million individuals for Mendelian randomization. RESULTS: Psoriatic patients have a significantly higher risk of MS (4,637 patients with both diseases; odds ratio [OR] 1.07, p = 1.2 × 10-5 ) after controlling for potential confounders. Using inverse variance and equally weighted trans-disease meta-analysis, we revealed >20 shared and opposing (direction of effect) genetic loci outside the major histocompatibility complex that showed significant genetic colocalization (in COLOC and COLOC-SuSiE v5.1.0). Co-expression analysis of genes from these loci further identified distinct clusters that were enriched among pathways for interleukin-17/tumor necrosis factor-α (OR >39, p < 1.6 × 10-3 ) and Janus kinase-signal transducers and activators of transcription (OR 35, p = 1.1 × 10-5 ), including genes, such as TNFAIP3, TYK2, and TNFRSF1A. Mendelian randomization found psoriasis as an exposure has a significant causal effect on MS (OR 1.04, p = 5.8 × 10-3 ), independent of type 1 diabetes (OR 1.05, p = 4.3 × 10-7 ), type 2 diabetes (OR 1.08, p = 2.3 × 10-3 ), inflammatory bowel disease (OR 1.11, p = 1.6 × 10-11 ), and vitamin D level (OR 0.75, p = 9.4 × 10-3 ). INTERPRETATION: By investigating the shared genetics of psoriasis and MS, along with their modifiable risk factors, our findings will advance innovations in treatment for patients suffering from comorbidities. ANN NEUROL 2023;94:384-397.

A short HLA-DRA isoform binds the HLA-DR2 heterodimer on the outer domain of the peptide-binding site.

The human leukocyte antigen (HLA) locus encodes a large group of proteins governing adaptive and innate immune responses. Among them, HLA class II proteins form α/ß heterodimers on the membrane of professional antigen-presenting cells (APCs), where they display both, self and pathogen-derived exogenous antigens to CD4+ T lymphocytes. We have previously shown that a shorter HLA-DRA isoform (sHLA-DRA) lacking 25 amino acids can be presented onto the cell membrane via binding to canonical HLA-DR2 heterodimers. Here, we employed atomistic molecular dynamics simulations to decipher the binding position of sHLA-DRA and its structural impact on functional regions of the HLA-DR2 molecule. We show that a loop region exposed only in the short isoform (residues R69 to G83) is responsible for binding to the outer domain of the HLA-DR2 peptide-binding site, and experimentally validated the critical role of F76 in mediating such interaction. Additionally, sHLA-DRA allosterically modifies the peptide-binding pocket conformation. In summary, this study unravels key molecular mechanisms underlying sHLA-DRA function, providing important insights into the role of full-length proteins in structural modulation of HLA class II receptors.

Progressive multifocal leukoencephalopathy genetic risk variants for pharmacovigilance of immunosuppressant therapies.

Background: Progressive multifocal leukoencephalopathy (PML) is a rare and often lethal brain disorder caused by the common, typically benign polyomavirus 2, also known as JC virus (JCV). In a small percentage of immunosuppressed individuals, JCV is reactivated and infects the brain, causing devastating neurological defects. A wide range of immunosuppressed groups can develop PML, such as patients with: HIV/AIDS, hematological malignancies (e.g., leukemias, lymphomas, and multiple myeloma), autoimmune disorders (e.g., psoriasis, rheumatoid arthritis, and systemic lupus erythematosus), and organ transplants. In some patients, iatrogenic (i.e., drug-induced) PML occurs as a serious adverse event from exposure to immunosuppressant therapies used to treat their disease (e.g., hematological malignancies and multiple sclerosis). While JCV infection and immunosuppression are necessary, they are not sufficient to cause PML. Methods: We hypothesized that patients may also have a genetic susceptibility from the presence of rare deleterious genetic variants in immune-relevant genes (e.g., those that cause inborn errors of immunity). In our prior genetic study of 184 PML cases, we discovered 19 candidate PML risk variants. In the current study of another 152 cases, we validated 4 of 19 variants in both population controls (gnomAD 3.1) and matched controls (JCV+ multiple sclerosis patients on a PML-linked drug ≥ 2 years). Results: The four variants, found in immune system genes with strong biological links, are: C8B, 1-57409459-C-A, rs139498867; LY9 (alias SLAMF3), 1-160769595-AG-A, rs763811636; FCN2, 9-137779251-G-A, rs76267164; STXBP2, 19-7712287-G-C, rs35490401. Carriers of any one of these variants are shown to be at high risk of PML when drug-exposed PML cases are compared to drug-exposed matched controls: P value = 3.50E-06, OR = 8.7 [3.7-20.6]. Measures of clinical validity and utility compare favorably to other genetic risk tests, such as BRCA1 and BRCA2 screening for breast cancer risk and HLA-B*15:02 pharmacogenetic screening for pharmacovigilance of carbamazepine to prevent Stevens-Johnson Syndrome and Toxic Epidermal Necrolysis. Conclusion: For the first time, a PML genetic risk test can be implemented for screening patients taking or considering treatment with a PML-linked drug in order to decrease the incidence of PML and enable safer use of highly effective therapies used to treat their underlying disease.

Next-Generation Sequencing Identifies Extended HLA Class I and II Haplotypes Associated With Early-Onset and Late-Onset Myasthenia Gravis in Italian, Norwegian, and Swedish Populations.

Genetic susceptibility to myasthenia gravis (MG) associates with specific HLA alleles and haplotypes at the class I and II regions in various populations. Previous studies have only examined alleles at a limited number of HLA loci that defined only broad serotypes or alleles defined at the protein sequence level. Consequently, genetic variants in noncoding and untranslated HLA gene segments have not been fully explored but could also be important determinants for MG. To gain further insight into the role of HLA in MG, we applied next-generation sequencing to analyze sequence variation at eleven HLA genes in early-onset (EO) and late-onset (LO) non-thymomatous MG patients positive for the acetylcholine receptor (AChR) antibodies and ethnically matched controls from Italy, Norway, and Sweden. For all three populations, alleles and haplotype blocks present on the ancestral haplotype AH8.1 were associated with risk in AChR-EOMG patients. HLA-B*08:01:01:01 was the dominant risk allele in Italians (OR = 3.28, P = 1.83E-05), Norwegians (OR = 3.52, P = 4.41E-16), and in Swedes HLA-B*08:01 was the primary risk allele (OR = 4.24, P <2.2E-16). Protective alleles and haplotype blocks were identified on the HLA-DRB7, and HLA-DRB13.1 class II haplotypes in Italians and Norwegians, whereas in Swedes HLA-DRB7 exhibited the main protective effect. For AChR-LOMG patients, the HLA-DRB15.1 haplotype and associated alleles were significantly associated with susceptibility in all groups. The HLA-DR13-HLA-DR-HLA-DQ haplotype was associated with protection in all AChR-LOMG groups. This study has confirmed and extended previous findings that the immunogenetic predisposition profiles for EOMG and LOMG are distinct. In addition, the results are consistent with a role for non-coding HLA genetic variants in the pathogenesis of MG.

A splice acceptor variant in HLA-DRA affects the conformation and cellular localization of the class II DR alpha-chain.

Class II human leucocyte antigen (HLA) proteins are involved in the immune response by presenting pathogen-derived peptides to CD4+ T lymphocytes. At the molecular level, they are constituted by α/ß-heterodimers on the surface of professional antigen-presenting cells. Here, we report that the acceptor variant (rs8084) in the HLA-DRA gene mediates the transcription of an alternative version of the α-chain lacking 25 amino acids in its extracellular domain. Molecular dynamics simulations suggest this isoform undergoes structural refolding which in turn affects its stability and cellular trafficking. The short HLA-DRA isoform cannot reach the cell surface, although it is still able to bind the corresponding ß-chain. Conversely, it remains entrapped within the endoplasmic reticulum where it is targeted for degradation. Furthermore, we demonstrate that the short isoform can be transported to the cell membrane via interactions with the peptide-binding site of canonical HLA heterodimers. Altogether, our findings indicate that short HLA-DRA functions as a novel intact antigen for class II HLA molecules.

Ataxin-1 regulates B cell function and the severity of autoimmune experimental encephalomyelitis.

Ataxin-1 (ATXN1) is a ubiquitous polyglutamine protein expressed primarily in the nucleus where it binds chromatin and functions as a transcriptional repressor. Mutant forms of ataxin-1 containing expanded glutamine stretches cause the movement disorder spinocerebellar ataxia type 1 (SCA1) through a toxic gain-of-function mechanism in the cerebellum. Conversely, ATXN1 loss-of-function is implicated in cancer development and Alzheimer's disease (AD) pathogenesis. ATXN1 was recently nominated as a susceptibility locus for multiple sclerosis (MS). Here, we show that Atxn1-null mice develop a more severe experimental autoimmune encephalomyelitis (EAE) course compared to wildtype mice. The aggravated phenotype is mediated by increased T helper type 1 (Th1) cell polarization, which in turn results from the dysregulation of B cell activity. Ataxin-1 ablation in B cells leads to aberrant expression of key costimulatory molecules involved in proinflammatory T cell differentiation, including cluster of differentiation (CD)44 and CD80. In addition, comprehensive phosphoflow cytometry and transcriptional profiling link the exaggerated proliferation of ataxin-1 deficient B cells to the activation of extracellular signal-regulated kinase (ERK) and signal transducer and activator of transcription (STAT) pathways. Lastly, selective deletion of the physiological binding partner capicua (CIC) demonstrates the importance of ATXN1 native interactions for correct B cell functioning. Altogether, we report a immunomodulatory role for ataxin-1 and provide a functional description of the ATXN1 locus genetic association with MS risk.

A specific amino acid motif of HLA-DRB1 mediates risk and interacts with smoking history in Parkinson's disease.

Parkinson's disease (PD) is a neurodegenerative disease in which genetic risk has been mapped to HLA, but precise allelic associations have been difficult to infer due to limitations in genotyping methodology. Mapping PD risk at highest possible resolution, we performed sequencing of 11 HLA genes in 1,597 PD cases and 1,606 controls. We found that susceptibility to PD can be explained by a specific combination of amino acids at positions 70-74 on the HLA-DRB1 molecule. Previously identified as the primary risk factor in rheumatoid arthritis and referred to as the "shared epitope" (SE), the residues Q/R-K/R-R-A-A at positions 70-74 in combination with valine at position 11 (11-V) is highly protective in PD, while risk is attributable to the identical epitope in the absence of 11-V. Notably, these effects are modified by history of cigarette smoking, with a strong protective effect mediated by a positive history of smoking in combination with the SE and 11-V (P = 10-4; odds ratio, 0.51; 95% confidence interval, 0.36-0.72) and risk attributable to never smoking in combination with the SE without 11-V (P = 0.01; odds ratio, 1.51; 95% confidence interval, 1.08-2.12). The association of specific combinations of amino acids that participate in critical peptide-binding pockets of the HLA class II molecule implicates antigen presentation in PD pathogenesis and provides further support for genetic control of neuroinflammation in disease. The interaction of HLA-DRB1 with smoking history in disease predisposition, along with predicted patterns of peptide binding to HLA, provide a molecular model that explains the unique epidemiology of smoking in PD.

Genome sequencing uncovers phenocopies in primary progressive multiple sclerosis.

OBJECTIVE: Primary progressive multiple sclerosis (PPMS) causes accumulation of neurological disability from disease onset without clinical attacks typical of relapsing multiple sclerosis (RMS). However, whether genetic variation influences the disease course remains unclear. We aimed to determine whether mutations causative of neurological disorders that share features with multiple sclerosis (MS) contribute to risk for developing PPMS. METHODS: We examined whole-genome sequencing (WGS) data from 38 PPMS and 81 healthy subjects of European ancestry. We selected pathogenic variants exclusively found in PPMS patients that cause monogenic neurological disorders and performed two rounds of replication genotyping in 746 PPMS, 3,049 RMS, and 1,000 healthy subjects. To refine our findings, we examined the burden of rare, potentially pathogenic mutations in 41 genes that cause hereditary spastic paraplegias (HSPs) in PPMS (n = 314), secondary progressive multiple sclerosis (SPMS; n = 587), RMS (n = 2,248), and healthy subjects (n = 987) genotyped using the MS replication chip. RESULTS: WGS and replication studies identified three pathogenic variants in PPMS patients that cause neurological disorders sharing features with MS: KIF5A p.Ala361Val in spastic paraplegia 10; MLC1 p.Pro92Ser in megalencephalic leukodystrophy with subcortical cysts, and REEP1 c.606 + 43G>T in Spastic Paraplegia 31. Moreover, we detected a significant enrichment of HSP-related mutations in PPMS patients compared to controls (risk ratio [RR] = 1.95; 95% confidence interval [CI], 1.27-2.98; p = 0.002), as well as in SPMS patients compared to controls (RR = 1.57; 95% CI, 1.18-2.10; p = 0.002). Importantly, this enrichment was not detected in RMS. INTERPRETATION: This study provides evidence to support the hypothesis that rare Mendelian genetic variants contribute to the risk for developing progressive forms of MS. Ann Neurol 2018;83:51-63.

IFN-γ orchestrates mesenchymal stem cell plasticity through the signal transducer and activator of transcription 1 and 3 and mammalian target of rapamycin pathways.

BACKGROUND: Mesenchymal stem cells (MSCs) display a therapeutic plasticity because of their ability to modulate immunity, foster tissue repair, and differentiate into mesodermal cells. IFN-γ has been described to differently affect human mesenchymal stem cell (hMSC) and mouse mesenchymal stem cell (mMSC) immunomodulation and differentiation, depending on the inflammatory milieu. OBJECTIVE: We aimed at dissecting the relevant intracellular pathways through which IFN-γ affects MSC plasticity and the consequence of their manipulation on MSC functions. METHODS: Modification of relevant IFN-γ-dependent pathways in mMSCs was carried out in vitro through gene silencing or chemical inhibition of key components. Functional outcomes were assessed by means of Western blotting, real-time PCR, differentiation, and proliferation assays on MSCs. The effect on T cells was addressed by T-cell proliferation assays; the effect of mammalian target of rapamycin (mTOR) manipulation in MSCs was studied in vivo in a mouse model of delayed-type hypersensitivity assay. To address whether similar mechanisms are involved also in hMSCs on IFN-γ stimulation, the effect of chemical inhibition on the same intracellular pathways was assessed by means of Western blotting, and the final outcome on immunomodulatory properties was evaluated based on real-time PCR and T-cell proliferation. RESULTS: We revealed that in mMSCs IFN-γ-induced immunoregulation is mediated by early phosphorylation of signal transducer and activator of transcription (STAT) 1 and STAT3, which is significantly enhanced by an extracellular signal-regulated kinase 1/2-dependent mTOR inhibition, thereby promoting pSTAT1 nuclear translocation. Accordingly, after intracellular mTOR inhibition, MSCs augmented their ability to inhibit T-cell proliferation and control delayed-type hypersensitivity in vivo. Similarly, on mTOR blockade, hMSCs also enhanced their immunoregulatory features. A sustained exposure to IFN-γ led to inhibition of STAT3 activity, which in mMSCs resulted in an impaired proliferation and differentiation. CONCLUSION: These results provide new insights about MSC intracellular pathways affected by IFN-γ, demonstrating that pharmacologic or genetic manipulation of MSCs can enhance their immunomodulatory functions, which could be translated into novel therapeutic approaches.

Defining KIR and HLA Class I Genotypes at Highest Resolution via High-Throughput Sequencing.

The physiological functions of natural killer (NK) cells in human immunity and reproduction depend upon diverse interactions between killer cell immunoglobulin-like receptors (KIRs) and their HLA class I ligands: HLA-A, HLA-B, and HLA-C. The genomic regions containing the KIR and HLA class I genes are unlinked, structurally complex, and highly polymorphic. They are also strongly associated with a wide spectrum of diseases, including infections, autoimmune disorders, cancers, and pregnancy disorders, as well as the efficacy of transplantation and other immunotherapies. To facilitate study of these extraordinary genes, we developed a method that captures, sequences, and analyzes the 13 KIR genes and HLA-A, HLA-B, and HLA-C from genomic DNA. We also devised a bioinformatics pipeline that attributes sequencing reads to specific KIR genes, determines copy number by read depth, and calls high-resolution genotypes for each KIR gene. We validated this method by using DNA from well-characterized cell lines, comparing it to established methods of HLA and KIR genotyping, and determining KIR genotypes from 1000 Genomes sequence data. This identified 116 previously uncharacterized KIR alleles, which were all demonstrated to be authentic by sequencing from source DNA via standard methods. Analysis of just two KIR genes showed that 22% of the 1000 Genomes individuals have a previously uncharacterized allele or a structural variant. The method we describe is suited to the large-scale analyses that are needed for characterizing human populations and defining the precise HLA and KIR factors associated with disease. The methods are applicable to other highly polymorphic genes.

Meta-analysis of genome-wide association studies reveals genetic overlap between Hodgkin lymphoma and multiple sclerosis.

BACKGROUND: Based on epidemiological commonalities, multiple sclerosis (MS) and Hodgkin lymphoma (HL), two clinically distinct conditions, have long been suspected to be aetiologically related. MS and HL occur in roughly the same age groups, both are associated with Epstein-Barr virus infection and ultraviolet (UV) light exposure, and they cluster mutually in families (though not in individuals). We speculated if in addition to sharing environmental risk factors, MS and HL were also genetically related. Using data from genome-wide association studies (GWAS) of 1816 HL patients, 9772 MS patients and 25 255 controls, we therefore investigated the genetic overlap between the two diseases. METHODS: From among a common denominator of 404 K single nucleotide polymorphisms (SNPs) studied, we identified SNPs and human leukocyte antigen (HLA) alleles independently associated with both diseases. Next, we assessed the cumulative genome-wide effect of MS-associated SNPs on HL and of HL-associated SNPs on MS. To provide an interpretational frame of reference, we used data from published GWAS to create a genetic network of diseases within which we analysed proximity of HL and MS to autoimmune diseases and haematological and non-haematological malignancies. RESULTS: SNP analyses revealed genome-wide overlap between HL and MS, most prominently in the HLA region. Polygenic HL risk scores explained 4.44% of HL risk (Nagelkerke R(2)), but also 2.36% of MS risk. Conversely, polygenic MS risk scores explained 8.08% of MS risk and 1.94% of HL risk. In the genetic disease network, HL was closer to autoimmune diseases than to solid cancers. CONCLUSIONS: HL displays considerable genetic overlap with MS and other autoimmune diseases.

High-density mapping of the MHC identifies a shared role for HLA-DRB1*01:03 in inflammatory bowel diseases and heterozygous advantage in ulcerative colitis.

Genome-wide association studies of the related chronic inflammatory bowel diseases (IBD) known as Crohn's disease and ulcerative colitis have shown strong evidence of association to the major histocompatibility complex (MHC). This region encodes a large number of immunological candidates, including the antigen-presenting classical human leukocyte antigen (HLA) molecules. Studies in IBD have indicated that multiple independent associations exist at HLA and non-HLA genes, but they have lacked the statistical power to define the architecture of association and causal alleles. To address this, we performed high-density SNP typing of the MHC in >32,000 individuals with IBD, implicating multiple HLA alleles, with a primary role for HLA-DRB1*01:03 in both Crohn's disease and ulcerative colitis. Noteworthy differences were observed between these diseases, including a predominant role for class II HLA variants and heterozygous advantage observed in ulcerative colitis, suggesting an important role of the adaptive immune response in the colonic environment in the pathogenesis of IBD.

In depth comparison of an individual's DNA and its lymphoblastoid cell line using whole genome sequencing.

BACKGROUND: A detailed analysis of whole genomes can be now achieved with next generation sequencing. Epstein Barr Virus (EBV) transformation is a widely used strategy in clinical research to obtain an unlimited source of a subject's DNA. Although the mechanism of transformation and immortalization by EBV is relatively well known at the transcriptional and proteomic level, the genetic consequences of EBV transformation are less well understood. A detailed analysis of the genetic alterations introduced by EBV transformation is highly relevant, as it will inform on the usefulness and limitations of this approach. RESULTS: We used whole genome sequencing to assess the genomic signature of a low-passage lymphoblastoid cell line (LCL). Specifically, we sequenced the full genome (40X) of an individual using DNA purified from fresh whole blood as well as DNA from his LCL. A total of 217.33 Gb of sequence were generated from the cell line and 238.95 Gb from the normal genomic DNA. We determined with high confidence that 99.2% of the genomes were identical, with no reproducible changes in structural variation (chromosomal rearrangements and copy number variations) or insertion/deletion polymorphisms (indels). CONCLUSIONS: Our results suggest that, at this level of resolution, the LCL is genetically indistinguishable from its genomic counterpart and therefore their use in clinical research is not likely to introduce a significant bias.

Evaluating the genomic and sequence integrity of human ES cell lines; comparison to normal genomes.

Copy number variation (CNV) is a common chromosomal alteration that can occur during in vitro cultivation of human cells and can be accompanied by the accumulation of mutations in coding region sequences. We describe here a systematic application of current molecular technologies to provide a detailed understanding of genomic and sequence profiles of human embryonic stem cell (hESC) lines that were derived under GMP-compliant conditions. We first examined the overall chromosomal integrity using cytogenetic techniques to determine chromosome count, and to detect the presence of cytogenetically aberrant cells in the culture (mosaicism). Assays of copy number variation, using both microarray and sequence-based analyses, provide a detailed view genomic variation in these lines and shows that in early passage cultures of these lines, the size range and distribution of CNVs are entirely consistent with those seen in the genomes of normal individuals. Similarly, genome sequencing shows variation within these lines that is completely within the range seen in normal genomes. Important gene classes, such as tumor suppressors and genetic disease genes, do not display overtly disruptive mutations that could affect the overall safety of cell-based therapeutics. Complete sequence also allows the analysis of important transplantation antigens, such as ABO and HLA types. The combined application of cytogenetic and molecular technologies provides a detailed understanding of genomic and sequence profiles of GMP produced ES lines for potential use as therapeutic agents.

Naive antibody gene-segment frequencies are heritable and unaltered by chronic lymphocyte ablation.

A diverse antibody repertoire is essential for an effective adaptive immune response to novel molecular surfaces. Although past studies have observed common patterns of V-segment use, as well as variation in V-segment use between individuals, the relative contributions to variance from genetics, disease, age, and environment have remained unclear. Using high-throughput sequence analysis of monozygotic twins, we show that variation in naive V(H) and D(H) segment use is strongly determined by an individual's germ-line genetic background. The inherited segment-use profiles are resilient to differential environmental exposure, disease processes, and chronic lymphocyte depletion therapy. Signatures of the inherited profiles were observed in class switched germ-line use of each individual. However, despite heritable segment use, the rearranged complementarity-determining region-H3 repertoires remained highly specific to the individual. As it has been previously demonstrated that certain V-segments exhibit biased representation in autoimmunity, lymphoma, and viral infection, we anticipate our findings may provide a unique mechanism for stratifying individual risk profiles in specific diseases.

Variation within DNA repair pathway genes and risk of multiple sclerosis.

Multiple sclerosis (MS) is a complex autoimmune disease of the central nervous system with a prominent genetic component. The primary genetic risk factor is the human leukocyte antigen (HLA)-DRB1*1501 allele; however, much of the remaining genetic contribution to MS has not been elucidated. The authors investigated the relation between variation in DNA repair pathway genes and risk of MS. Single-locus association testing, epistatic tests of interactions, logistic regression modeling, and nonparametric Random Forests analyses were performed by using genotypes from 1,343 MS cases and 1,379 healthy controls of European ancestry. A total of 485 single nucleotide polymorphisms within 72 genes related to DNA repair pathways were investigated, including base excision repair, nucleotide excision repair, and double-strand breaks repair. A single nucleotide polymorphism variant within the general transcription factor IIH, polypeptide 4 gene, GTF2H4, on chromosome 6p21.33 was significantly associated with MS (odds ratio = 0.7, P = 3.5 x 10(-5)) after accounting for multiple testing and was not due to linkage disequilibrium with HLA-DRB1*1501. Although other candidate genes examined here warrant further follow-up studies, collectively, these results derived from a well-powered study do not support a strong role for common variation within DNA repair pathway genes in MS.

Genome, epigenome and RNA sequences of monozygotic twins discordant for multiple sclerosis.

Monozygotic or 'identical' twins have been widely studied to dissect the relative contributions of genetics and environment in human diseases. In multiple sclerosis (MS), an autoimmune demyelinating disease and common cause of neurodegeneration and disability in young adults, disease discordance in monozygotic twins has been interpreted to indicate environmental importance in its pathogenesis. However, genetic and epigenetic differences between monozygotic twins have been described, challenging the accepted experimental model in disambiguating the effects of nature and nurture. Here we report the genome sequences of one MS-discordant monozygotic twin pair, and messenger RNA transcriptome and epigenome sequences of CD4(+) lymphocytes from three MS-discordant, monozygotic twin pairs. No reproducible differences were detected between co-twins among approximately 3.6 million single nucleotide polymorphisms (SNPs) or approximately 0.2 million insertion-deletion polymorphisms. Nor were any reproducible differences observed between siblings of the three twin pairs in HLA haplotypes, confirmed MS-susceptibility SNPs, copy number variations, mRNA and genomic SNP and insertion-deletion genotypes, or the expression of approximately 19,000 genes in CD4(+) T cells. Only 2 to 176 differences in the methylation of approximately 2 million CpG dinucleotides were detected between siblings of the three twin pairs, in contrast to approximately 800 methylation differences between T cells of unrelated individuals and several thousand differences between tissues or between normal and cancerous tissues. In the first systematic effort to estimate sequence variation among monozygotic co-twins, we did not find evidence for genetic, epigenetic or transcriptome differences that explained disease discordance. These are the first, to our knowledge, female, twin and autoimmune disease individual genome sequences reported.

Meta-analysis of genome scans and replication identify CD6, IRF8 and TNFRSF1A as new multiple sclerosis susceptibility loci.

We report the results of a meta-analysis of genome-wide association scans for multiple sclerosis (MS) susceptibility that includes 2,624 subjects with MS and 7,220 control subjects. Replication in an independent set of 2,215 subjects with MS and 2,116 control subjects validates new MS susceptibility loci at TNFRSF1A (combined P = 1.59 x 10(-11)), IRF8 (P = 3.73 x 10(-9)) and CD6 (P = 3.79 x 10(-9)). TNFRSF1A harbors two independent susceptibility alleles: rs1800693 is a common variant with modest effect (odds ratio = 1.2), whereas rs4149584 is a nonsynonymous coding polymorphism of low frequency but with stronger effect (allele frequency = 0.02; odds ratio = 1.6). We also report that the susceptibility allele near IRF8, which encodes a transcription factor known to function in type I interferon signaling, is associated with higher mRNA expression of interferon-response pathway genes in subjects with MS.

Differential impact of the CD45 juxtamembrane wedge on central and peripheral T cell receptor responses.

The cooperative activity of protein tyrosine kinases and phosphatases plays a central role in regulation of T cell receptor (TCR) signal strength. Perturbing this balance, and thus the threshold for TCR signals, has profound impacts on T cell development and function. We previously generated mice containing a point mutation in the juxtamembrane wedge of the receptor-like protein tyrosine phosphatase CD45. Demonstrating the critical negative regulatory function of the wedge, the CD45 E613R (WEDGE) mutation led to a lymphoproliferative disorder (LPD) and a lupus-like autoimmune syndrome. Using genetic, cellular, and biochemical approaches, we now demonstrate that the CD45 wedge influences T cell development and function. Consistent with increased TCR signal strength, WEDGE mice have augmented positive selection and enhanced sensitivity to the CD4-mediated disease experimental autoimmune encephalitis (EAE). These correspond with hyperresponsive calcium and pERK responses to TCR stimulation in thymocytes, but surprisingly, not in peripheral T cells, where these responses are actually depressed. Together, the data support a role for the CD45 wedge in regulation of T cell responses in vivo and suggest that its effects depend on cellular context.

Abrogation of T cell quiescence characterizes patients at high risk for multiple sclerosis after the initial neurological event.

Clinically isolated syndrome (CIS) refers to the earliest clinical manifestation of multiple sclerosis (MS). Currently there are no prognostic biological markers that accurately predict conversion of CIS to clinically definite MS (CDMS). Furthermore, the earliest molecular events in MS are still unknown. We used microarrays to study gene expression in naïve CD4(+) T cells from 37 CIS patients at time of diagnosis and after 1 year. Supervised machine-learning methods were used to build predictive models of disease conversion. We identified 975 genes whose expression segregated CIS patients into four distinct subgroups. A subset of 108 genes further discriminated patients in one of these (group 1) from other CIS patients. Remarkably, 92% of patients in group 1 converted to CDMS within 9 months. Consistent down-regulation of TOB1, a critical regulator of cell proliferation, was characteristic of group 1 patients. Decreased TOB1 expression at the RNA and protein levels also was confirmed in experimental autoimmune encephalomyelitis. Finally, a genetic association was observed between TOB1 variation and MS progression in an independent cohort. These results indicate that CIS patients at high risk of conversion have impaired regulation of T cell quiescence, possibly resulting in earlier activation of pathogenic CD4(+) cells.