The Canadian Collaborative Project on Genetic Susceptibility to Multiple Sclerosis cohort population structure and disease etiology.

Background: Previous genetic and epidemiological studies have examined subpopulations from the Canadian Collaborative Project on Genetic Susceptibility to Multiple Sclerosis (CCPGSMS) patient cohort, but an encompassing analysis of the study population has not yet been carried out. Objective: This study examines patterns of multiple sclerosis (MS) prevalence in 13,663 cohort members, including 4,821 patients with MS or suspected MS and 8,842 family members. Methods: We grouped participants into epidemiologic subgroups based on age of MS onset, clinical stage at diagnosis, symptom type at disease onset, sex, proband status, disability as measured by the EDSS, and ancestry based on reported ethnicity. Results: We observed a 2.7:1 MS prevalence ratio of women to men, though disease severity was greater for male patients. Variation in the age of disease onset between patients was only slightly associated with sex and strongly associated with disease type. Specific types of clinical symptoms at disease onset were associated with the prognosis. Regional residence did not correlate with disease onset, type, or severity. Conclusion: Population trends, as presented here, are not explained by environmental factors alone, highlighting the need for a comprehensive genetic analysis to understand disease variance across families.

A Whole-Genome Sequencing Study Implicates GRAMD1B in Multiple Sclerosis Susceptibility.

While the role of common genetic variants in multiple sclerosis (MS) has been elucidated in large genome-wide association studies, the contribution of rare variants to the disease remains unclear. Herein, a whole-genome sequencing study in four affected and four healthy relatives of a consanguineous Italian family identified a novel missense c.1801T > C (p.S601P) variant in the GRAMD1B gene that is shared within MS cases and resides under a linkage peak (LOD: 2.194). Sequencing GRAMD1B in 91 familial MS cases revealed two additional rare missense and two splice-site variants, two of which (rs755488531 and rs769527838) were not found in 1000 Italian healthy controls. Functional studies demonstrated that GRAMD1B, a gene with unknown function in the central nervous system (CNS), is expressed by several cell types, including astrocytes, microglia and neurons as well as by peripheral monocytes and macrophages. Notably, GRAMD1B was downregulated in vessel-associated astrocytes of active MS lesions in autopsied brains and by inflammatory stimuli in peripheral monocytes, suggesting a possible role in the modulation of inflammatory response and disease pathophysiology.

Peripartum disease activity in moderately and severely disabled women with multiple sclerosis.

Background: The effects of pregnancy on multiple sclerosis (MS) inflammatory activity are not well described in women with moderate to severe disabilities. Objective: To quantify the peripartum annualized relapse rate (ARR) in women with MS with an Expanded Disability Status Scale (EDSS) ≥ 3. Methods: We performed a retrospective cohort study of 85 pregnancies in 74 subjects with preconception EDSS ≥ 3. We quantified peripartum ARR and tested for risk factors predictive of peripartum relapses, postpartum brain magnetic resonance imaging activity (new T2 or gadolinium-enhancing lesions), and disability worsening. Results: There were 74 live births, with a 56% operative delivery rate. In subjects with relapsing-remitting MS, ARR decreased to 0.11 during the third trimester of pregnancy compared to 0.59 in the year preconception and increased to 1.22 in the 3 months postpartum. Women with a higher preconception EDSS had higher odds of postpartum relapses and clinically significant worsening of disability as compared to subjects with a lower EDSS. Conclusions: Moderately to severely disabled women with MS have a lower risk of relapse during pregnancy as compared to preconception, followed by a marked increase postpartum. Further studies are needed to identify ways to reduce peripartum inflammatory activity and disability progression in women with MS with moderate to severe disability.

Cortical morphology predicts placebo response in multiple sclerosis.

Despite significant insights into the neural mechanisms of acute placebo responses, less is known about longer-term placebo responses, such as those seen in clinical trials, or their interactions with brain disease. We examined brain correlates of placebo responses in a randomized trial of a then controversial and now disproved endovascular treatment for multiple sclerosis. Patients received either balloon or sham extracranial venoplasty and were followed for 48 weeks. Venoplasty had no therapeutic effect, but a subset of both venoplasty- and sham-treated patients reported a transient improvement in health-related quality of life, suggesting a placebo response. Placebo responders did not differ from non-responders in total MRI T2 lesion load, count or location, nor were there differences in normalized brain volume, regional grey or white matter volume or cortical thickness (CT). However, responders had higher lesion activity. Graph theoretical analysis of CT covariance showed that non-responders had a more small-world-like CT architecture. In non-responders, lesion load was inversely associated with CT in somatosensory, motor and association areas, precuneus, and insula, primarily in the right hemisphere. In responders, lesion load was unrelated to CT. The neuropathological process in MS may produce in some a cortical configuration less capable of generating sustained placebo responses.

Genes and environment in multiple sclerosis: Impact of temporal changes in the sex ratio on recurrence risks.

OBJECTIVE: To evaluate the impact of temporal increase of female to male (F:M) sex ratio for persons with multiple sclerosis (MS) on the familial risk (empiric recurrence risks or RRs) for biological relatives of affected individuals. METHODS: Detailed family histories were systematically obtained from people with MS attending the University of British Columbia Hospital MS Clinic. The study cohort was born in 1970 or more recently. Data were collected from 1 September 2015 to 31 January 2019. The study was designed to allow only one proband per family. Age-corrected RRs for biological relatives of probands were calculated based on a modification of the maximum-likelihood approach. RESULTS: Data analyses were possible for 746 unique probands (531 females; 215 males) and 19,585 of their biological relatives. RRs were temporally impacted. CONCLUSION: Both genetic sharing and environmental factors are important in determining RRs. It appears that there is an increase in MS risk due to environmental factors in later life (i.e. not shared family environment). Environmental exposures in genetically predisposed individuals might be driving the MS risk. The increase in F:M ratio of RRs for sisters/brothers of female probands over time is likely due to environmental differences.

Risk factors for peripartum depression in women with multiple sclerosis.

BACKGROUND: Peripartum depression (PPD) is underexplored in multiple sclerosis (MS). OBJECTIVE: To evaluate prevalence of and risk factors for PPD in women with MS. METHODS: Retrospective single-center analysis of women with MS with a live birth. Prevalence of PPD was estimated with logistic regression with generalized estimating equations (GEE). GEE evaluated predictors of PPD (e.g. age, marital status, parity, pre-pregnancy depression/anxiety, antidepressant discontinuation, sleep disturbance, breastfeeding, relapses, gadolinium-enhancing lesions, and disability). Factors significant in univariable analyses were included in multivariable analysis. RESULTS: We identified 143 live births in 111 women (mean age 33.1 ± 4.7 years). PPD was found in 18/143 pregnancies (12.6%, 95% CI = 7.3-17.8). Factors associated with PPD included older age (OR 1.16, 95% CI = 1.03-1.32 for 1-year increase), primiparity (OR 4.02, CI = 1.14-14.23), pre-pregnancy depression (OR 3.70, CI = 1.27-10.01), sleep disturbance (OR 3.23, CI = 1.17-8.91), and breastfeeding difficulty (OR 3.58, CI = 1.27-10.08). Maternal age (OR 1.17, CI = 1.02-1.34), primiparity (OR 8.10, CI = 1.38-47.40), and pre-pregnancy depression (OR 3.89, CI = 1.04-14.60) remained significant in multivariable analyses. Relapses, MRI activity, and disability were not associated with PPD. CONCLUSION: The prevalence of PPD in MS appeared similar to the general population, but was likely underestimated due to lack of screening. PPD can affect MS self-management and offspring development, and prospective studies are needed.

Genetic analysis of nucleotide-binding leucine-rich repeat (NLR) receptors in multiple sclerosis.

Genetic and functional analyses of the inflammasome suggest a role for this multiprotein complex in the biological mechanisms leading to the onset and progression of multiple sclerosis (MS). Nucleotide-binding, leucine-rich repeat (NLR) receptors trigger the activation and assembly of specific inflammasomes in response to danger signals. Mining exome sequencing data from 326 MS patients identified 17 rare missense or nonsense variants in NLR family pyrin domain containing 1 (NLRP1), NLRP3, NLRP6, NLRP7 and NLR family CARD domain containing 4 (NLRC4). Genotyping these variants in 2503 MS cases and 1076 healthy controls did not result in statistically significant differences between groups, and segregation analysis within MS families was largely unsupportive of co-segregation of these variants with disease. However, the identification of MS patients harboring rare homozygote variants in NLRP1 (p.Ile601Phe and p.Ser1387Ile), a variant in NLRP3 (p.Leu832Ile) resulting in the substitution of a critical amino acid for the formation of its leucine-rich repeat domain, and several MS patients with NLRC4 variants (p.Arg310Ter and p.Glu600Ter) causing protein truncations suggest that rare protein-altering variants in inflammasome-activating NLR receptors may contribute to MS risk.

Canadian Multiple Sclerosis Pregnancy Study (CANPREG-MS): Rationale and Methodology.

BACKGROUND: Multiple sclerosis (MS) is the most common cause of neurological disability, other than trauma, among young adults of reproductive age. In contrast to the past, today there is very little lag time from clinical onset to diagnosis. Disease-modifying therapies are also now available outside of clinical trials. However, there is very little evidence-based population data to help an individual with MS make informed decisions with respect to reproductive options. OBJECTIVE: The objective of this study is to develop a Canada-wide, prospective population-based registry of women with MS who are either trying to become pregnant and/or have become pregnant. METHODS: The study represents a "real-world" scenario. Women with MS are invited to participate, regardless of clinical course, therapy, disease duration, and/or disability. The methodology to develop such a registry is very complex making it imperative to understand the design and rationale when interpreting results for clinical purposes. RESULTS: This paper is a comprehensive discussion of the study rationale and methodology. CONCLUSIONS: The study is ongoing, with over 100 potential participants. Numerous future publications are envisioned as the study progresses. The present paper is thus designed to be the key referral paper for subsequent publications in which it will not be possible to provide the necessary detailed information on rationale and methodology.

Fondements et méthodologie de l'étude de cohorte prospective canadienne sur la grossesse dans le contexte de la sclérose en plaques. Contexte : Outre les traumatismes, la sclérose en plaques (SP) demeure la cause la plus fréquente d'invalidité neurologique parmi les jeunes adultes en âge de procréer. Contrairement au passé, les délais entre l'apparition des premiers signes cliniques de SP et un diagnostic sont de nos jours passablement courts. Qui plus est, des traitements modificateurs de la maladie (TMM) sont dorénavant disponibles en dehors d'un contexte d'essais cliniques. Cela dit, il existe encore peu de données probantes basées sur des études populationnelles en vue d'aider une personne atteinte de la SP à prendre des décisions éclairées quant à ses options en matière de reproduction. Objectif : L'objectif de cette étude est d'élaborer, à l'échelle canadienne, un registre prospectif de femmes atteintes de SP qui essaient de devenir enceintes et/ou qui le sont devenues. Méthodes : Cette étude repose sur un scénario ancré dans « la vie réelle ¼. Ainsi, des femmes atteintes de SP ont été invitées à y participer quels que soient l'évolution clinique de leur état de santé, leurs traitements, la durée de leur maladie et/ou leur degré d'invalidité. La méthodologie permettant d'élaborer un tel registre demeure très complexe, ce qui rend impérieux la compréhension de sa conception et de ses fondements au moment d'interpréter nos résultats à des fins cliniques. Résultats : Cet article constitue une discussion approfondie de la méthodologie et des fondements de cette étude. Conclusions : Toujours en cours, cette étude peut compter sur plus de 100 participants potentiels. De nombreuses publications subséquentes sont également envisagées au fur et à mesure de sa progression. Le présent article est par conséquent destiné à devenir une référence clé pour d'autres articles dans lesquels il ne sera pas possible d'indiquer tous les renseignements détaillés en ce qui regarde la méthodologie et les fondements de cette étude.

NLRX1 inhibits the early stages of CNS inflammation and prevents the onset of spontaneous autoimmunity.

Nucleotide-binding, leucine-rich repeat containing X1 (NLRX1) is a mitochondria-located innate immune sensor that inhibits major pro-inflammatory pathways such as type I interferon and nuclear factor-κB signaling. We generated a novel, spontaneous, and rapidly progressing mouse model of multiple sclerosis (MS) by crossing myelin-specific T-cell receptor (TCR) transgenic mice with Nlrx1-/- mice. About half of the resulting progeny developed spontaneous experimental autoimmune encephalomyelitis (spEAE), which was associated with severe demyelination and inflammation in the central nervous system (CNS). Using lymphocyte-deficient mice and a series of adoptive transfer experiments, we demonstrate that genetic susceptibility to EAE lies within the innate immune compartment. We show that NLRX1 inhibits the subclinical stages of microglial activation and prevents the generation of neurotoxic astrocytes that induce neuronal and oligodendrocyte death in vitro. Moreover, we discovered several mutations within NLRX1 that run in MS-affected families. In summary, our findings highlight the importance of NLRX1 in controlling the early stages of CNS inflammation and preventing the onset of spontaneous autoimmunity.

Exome sequencing in multiple sclerosis families identifies 12 candidate genes and nominates biological pathways for the genesis of disease.

Multiple sclerosis (MS) is an inflammatory disease of the central nervous system characterized by myelin loss and neuronal dysfunction. Although the majority of patients do not present familial aggregation, Mendelian forms have been described. We performed whole-exome sequencing analysis in 132 patients from 34 multi-incident families, which nominated likely pathogenic variants for MS in 12 genes of the innate immune system that regulate the transcription and activation of inflammatory mediators. Rare missense or nonsense variants were identified in genes of the fibrinolysis and complement pathways (PLAU, MASP1, C2), inflammasome assembly (NLRP12), Wnt signaling (UBR2, CTNNA3, NFATC2, RNF213), nuclear receptor complexes (NCOA3), and cation channels and exchangers (KCNG4, SLC24A6, SLC8B1). These genes suggest a disruption of interconnected immunological and pro-inflammatory pathways as the initial event in the pathophysiology of familial MS, and provide the molecular and biological rationale for the chronic inflammation, demyelination and neurodegeneration observed in MS patients.

Increased mean R2* in the deep gray matter of multiple sclerosis patients: Have we been measuring atrophy?

BACKGROUND: Magnetic resonance relaxometry studies in multiple sclerosis (MS) have suggested that iron accumulates within deep gray matter (DGM) structures early in the disease course. However, the commonly utilized mean R2* and magnetic susceptibility measures reflect regional iron concentration but not a structure's total iron content. Thus, tissue atrophy could impact mean R2* and magnetic susceptibility estimates. PURPOSE: To demonstrate that both average iron concentration and total iron content need to be reported in order to distinguish between atrophy-related and definite magnetic susceptibility changes. STUDY TYPE: Observational. POPULATION: The study was performed on 30 healthy controls (HCs) and 39 people with definite MS. FIELD STRENGTH/SEQUENCE: 3T Philips Achieva using an 8-channel SENSE head coil. R2* data were acquired using a multiecho gradient echo sequence and diffusion tensor imaging data were acquired using an echo-planar sequence. ASSESSMENT: Total iron content in DGM structures was assessed by calculating the sum of all R2* values within a region (denoted as R2mass* ) and compared to the mean R2* as a measure of iron concentration. STATISTICAL TEST: Significant group differences were investigated in a linear regression model. All DGM structures were assessed individually and the significance threshold was adjusted using the Bonferroni-Holm correction for multiple comparisons. RESULTS: There was an increased mean DGM R2* in MS patients compared to HCs (significant in the pallidus, P = 0.0051). In contrast, R2mass* in patients was found to be lower in the thalamus and the caudate (P = 0.0011) compared to HCs, and similar between the two cohorts in the other DGM regions. DATA CONCLUSION: An increase in mean R2* may not necessarily reflect increased iron accumulation. We propose R2mass* as an additional metric to account for the effects of tissue atrophy when assessing tissue content changes, such as iron deposition or loss. LEVEL OF EVIDENCE: 1 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2019;50:201-208.

TPP2 mutation associated with sterile brain inflammation mimicking MS.

OBJECTIVE: To ascertain the genetic cause of a consanguineous family from Syria suffering from a sterile brain inflammation mimicking a mild nonprogressive form of MS. METHODS: We used homozygosity mapping and next-generation sequencing to detect the disease-causing gene in the affected siblings. In addition, we performed RNA and protein expression studies, enzymatic activity assays, immunohistochemistry, and targeted sequencing of further MS cases from Austria, Germany, Canada and Jordan. RESULTS: In this study, we describe the identification of a homozygous missense mutation (c.82T>G, p.Cys28Gly) in the tripeptidyl peptidase II (TPP2) gene in all 3 affected siblings of the family. Sequencing of all TPP2-coding exons in 826 MS cases identified one further homozygous missense variant (c.2027C>T, p.Thr676Ile) in a Jordanian MS patient. TPP2 protein expression in whole blood was reduced in the affected siblings. In contrast, TPP2 protein expression in postmortem brain tissue from MS patients without TPP2 mutations was highly upregulated. CONCLUSIONS: The homozygous TPP2 mutation (p.Cys28Gly) is likely responsible for the inflammation phenotype in this family. TPP2 is an ubiquitously expressed serine peptidase that removes tripeptides from the N-terminal end of longer peptides. TPP2 is involved in various biological processes including the destruction of major histocompatibility complex Class I epitopes. Recessive loss-of-function mutations in TPP2 were described in patients with Evans syndrome, a rare autoimmune disease affecting the hematopoietic system. Based on the gene expression results in our MS autopsy brain samples, we further suggest that TPP2 may play a broader role in the inflammatory process in MS.

Safety and efficacy of venoplasty in MS: A randomized, double-blind, sham-controlled phase II trial.

OBJECTIVE: To determine the safety and efficacy of balloon vs sham venoplasty of narrowing of the extracranial jugular and azygos veins in multiple sclerosis (MS). METHODS: Patients with relapsing or progressive MS were screened using clinical and ultrasound criteria. After confirmation of >50% narrowing by venography, participants were randomized 1:1 to receive balloon or sham venoplasty of all stenoses and were followed for 48 weeks. Participants and research staff were blinded to intervention allocation. The primary safety outcome was the number of adverse events (AEs) during 48 weeks. The primary efficacy outcome was the change from baseline to week 48 in the patient-reported outcome MS Quality of Life-54 (MSQOL-54) questionnaire. Standardized clinical and MRI outcomes were also evaluated. RESULTS: One hundred four participants were randomized (55 sham; 49 venoplasty) and 103 completed 48 weeks of follow-up. Twenty-three sham and 21 venoplasty participants reported at least 1 AE; one sham (2%) and 5 (10%) venoplasty participants had a serious AE. The mean improvement in MSQOL-54 physical score was +1.3 (sham) and +1.4 (venoplasty) (p = 0.95); MSQOL-54 mental score was +1.2 (sham) and -0.8 (venoplasty) (p = 0.55). CONCLUSIONS: Our data do not support the continued use of venoplasty of extracranial jugular and/or azygous venous narrowing to improve patient-reported outcomes, chronic MS symptoms, or the disease course of MS. CLINICALTRIALSGOV IDENTIFIER: NCT01864941. CLASSIFICATION OF EVIDENCE: This study provides Class I evidence that for patients with MS, balloon venoplasty of extracranial jugular and azygous veins is not beneficial in improving patient-reported, standardized clinical, or MRI outcomes.

Analysis of NOD-like receptor NLRP1 in multiple sclerosis families.

The implementation of exome sequencing technologies has started to unravel the genetic etiology of familial multiple sclerosis (MS). A homozygote p.G587S mutation in NLRP1 has been suggested as potentially causative for the onset of MS in an affected sibling pair, who later developed malignant melanoma. To validate the proposed role of recessive NLRP1 mutations in the pathological mechanisms of MS, we examined exome sequencing data from 326 MS patients from Canada for the identification of NLRP1 missense and nonsense variants. This analysis did not identify the previously described p.G587S mutation; however, three patients with potential NLRP1 compound heterozygote mutations were observed. Haplotype and segregation analyses indicate that the variants observed in these patients were inherited in cis, and do not segregate with disease within families. Thus, the analysis of MS patients from Canada failed to identify potentially pathogenic mutations in NLRP1, including the previously described p.G587S mutation. Further studies are necessary to confirm a role of NLRP1 in the pathophysiology of MS.

Genetic modifiers of multiple sclerosis progression, severity and onset.

The genetic contribution to clinical outcomes for multiple sclerosis (MS) has yet to be defined. We performed exome sequencing analysis in 100 MS patients presenting opposite extremes of clinical phenotype (discovery cohort), and genotyped variants of interest in 2016 MS patients (replication cohort). Linear and logistic regression analyses were used to identify significant associations with disease course, severity and onset. Our analysis of the discovery cohort nominated 38 variants in 21 genes. Replication analysis identified PSMG4 p.W99R and NLRP5 p.M459I to be associated with disease severity (p=0.002 and 0.008). CACNA1H p.R1871Q was found associated with patients presenting relapsing remitting MS at clinical onset (p=0.028) whereas NLRP5 p.M459I and EIF2AK1 p.K558R were associated with primary progressive disease (p=0.031 and 0.023). In addition, PSMG4 p.W99R and NLRP5 p.R761L were found to correlate with an earlier age at MS clinical onset, and MC1R p.R160W with delayed onset of clinical symptoms (p=0.010-0.041).

Patient-Reported Benefits of Extracranial Venous Therapy: British Columbia CCSVI Registry.

Objective Chronic cerebrospinal venous insufficiency (CCSVI) has been hypothesized to be a risk factor for multiple sclerosis (MS). Venoplasty has been proposed as a treatment for CCSVI. The aim of our study was to gain a better understanding of the "real-world" safety and longitudinal effectiveness of venoplasty Methods: British Columbia residents who self-reported having had venoplasty and consented to participate in the study were interviewed and followed for up to 24 months post-therapy using standardized structured questionnaires Results: Participants reported procedure-related complications (11.5%) and complications within the first month after the procedure (17.3%). Initially, more than 40% of participants perceived that the venoplasty had had positive effects on their health conditions, such as fatigue, numbness, balance, concentration/memory and mobility. However, this improvement was not maintained over time Conclusions: Follow-up patient-reported outcomes indicated that the initial perception of the positive impact of venoplasty on the health conditions of MS patients was not sustained over time. In addition, venoplasty was not without associated morbidity.

Purinergic receptors P2RX4 and P2RX7 in familial multiple sclerosis.

Genetic variants in the purinergic receptors P2RX4 and P2RX7 have been shown to affect susceptibility to multiple sclerosis (MS). In this study, we set out to evaluate whether rare coding variants of major effect could also be identified in these purinergic receptors. Sequencing analysis of P2RX4 and P2RX7 in 193 MS patients and 100 controls led to the identification of a rare three variant haplotype (P2RX7 rs140915863:C>T [p.T205M], P2RX7 rs201921967:A>G [p.N361S], and P2RX4 rs765866317:G>A [p.G135S]) segregating with disease in a multi-incident family with six family members diagnosed with MS (logarithm of odds = 3.07). Functional analysis of this haplotype in HEK293 cells revealed impaired P2X7 surface expression (P < 0.01), resulting in over 95% inhibition of adenosine triphosphate (ATP)-induced pore function (P < 0.001) and a marked reduction in phagocytic ability (P < 0.05). In addition, transfected cells showed 40% increased peak ATP-induced inward current (P < 0.01), and a greater Ca2+ response to the P2X4 135S variant compared with wild type (P < 0.0001). Our study nominates rare genetic variants in P2RX4 and P2RX7 as major genetic contributors to disease, further supporting a role for these purinergic receptors in MS and the disruption of transmembrane cation channels leading to impairment of phagocytosis as the pathological mechanisms of disease.

Common genetic etiology between "multiple sclerosis-like" single-gene disorders and familial multiple sclerosis.

Several single-gene disorders with clinical and radiological characteristics similar to those observed in multiple sclerosis (MS) patients have been described. To evaluate whether this phenotypic overlap can be ascribed to a common genetic etiology, 28 genes known to present pathogenic mutations for 24 of these disorders were sequenced in 270 MS patients. All identified variants were genotyped in 2131 MS cases and 830 healthy controls, and those exclusively observed in patients were assessed for segregation within families. This analysis identified 9 rare variants in 6 genes segregating with disease in 13 families. Four different mutations were identified in CYP27A1, including a reported pathogenic mutation for cerebrotendinous xanthomatosis (p.R405W), which was observed in six patients from a multi-incident family, three diagnosed with MS, two with an undefined neurological disease and one seemingly healthy. A LYST p.V1678A and a PDHA1 p.K387Q mutation were both observed in five MS patients from three separate multi-incident families. In addition, CLCN2 p.V174G, GALC p.D162E and POLG p.R361G were each identified in two MS patients from one family. This study suggests a shared genetic etiology between MS and the characterized single-gene disorders, and highlights cholesterol metabolism and the synthesis of oxysterols as important biological mechanisms for familial MS.