Genetic susceptibility to multiple sclerosis

The Increased Susceptibility of Women to Multiple Sclerosis

Many diseases with an auto-immune etiology have a skewed sex distribution. In the majority of instances, women are affected more frequently than men. A review of population studies demonstrates that the preponderance of women in multiple sclerosis (MS) is almost constant. We show that this preponderance is further increased in early as well as in late-onset cases, in familial cases as well as in MS twin pairs and that the HLA-DR2 allele, which has been associated with MS in Caucasian populations, is significantly more frequent in women than in men with MS. “Rules” have been established for multifactorial diseases; MS contravenes most of those rules. The skewed sex distribution in MS could be attributed to the known hormonal and gender influences on the immune response, as well as to genetic influences.

The genetic basis of autoimmune disease

The genetic predisposition to autoimmune disease in man is largely specific for each disease, indicating that these diseases are based not on a generalized breakdown of a tolerance mechanism, but on highly specific abnormalities of immune responsiveness which are subject to genetic transmission. In the presence of particular antigens encoded in the major histocompatibility complex (MHC) the relative risk of certain autoimmune diseases is increased, or in some cases decreased, and the increased risk has been widely attributed to linkage disequilibrium with unidentified disease-causing genes. Our studies on the inheritance of spontaneous autoimmune diseases in New Zealand mice have revealed that small numbers of dominant genes, some associated with the MHC but the remainder elsewhere in the genome, determine susceptibility to these diseases. That MHC-linked genes are not of paramount importance casts doubt on the linkage disequilibrium hypothesis. An alternative possibility is that major and minor histocompatibility antigens themselves predispose to the development of autoimmune diseases by altering the immune response repertoire through the effect of their clonal deletions on the network of paratope-idiotope clonal interactions. Such alterations could influence the chances of emergence, by somatic mutation, of pathogenic forbidden clones.

Magnetisation transfer ratio analysis of normal appearing white matter in patients with familial and sporadic multiple sclerosis

OBJECTIVES

To assess differences in magnetisation transfer ratio (MTR) analysis of normal appearing white matter (NAWM) in patients with familial multiple sclerosis (MS) and those with sporadic MS.

METHODS

10 patients with familial MS, 10 patients with sporadic MS, and 10 healthy subjects were included in the study. Groups were matched according to the sex, age, disease duration, type of disease, EDSS, and MRI T1 and T2 lesion load. Magnetisation transfer imaging (MTI) with and without saturation pulse were performed. On the MTR map 16 different regions of interest of normal appearing white matter were analyzed.

RESULTS

The mean MTR value of normal appearing white matter was significantly lower both in familial patients and those with sporadic MS compared with healthy subjects (33.8% v 46.4%; 38.6% v 46.4% respectively, p< 0.05). Additionally, patients with familial MS showed significantly lower mean MTR value than patients with sporadic MS (33.8% v 38.6%, p<0.05). There was also significant regional variation of MTR values between these two groups of patients.

CONCLUSIONS

Lower and more widespread MTR abnormalities in patients with familial MS might indicate differences in the extent and nature of white matter pathology between familial and sporadic MS.

Multiple sclerosis: multiple etiologies, multiple genes?

Multiple sclerosis is a chronic inflammatory disease characterized by multifocal damage of the central nervous system myelin. Both humoral and cell-mediated immune abnormalities have been observed in patients with multiple sclerosis, but their relation to the demyelination process is not understood. The etiology of the disease is still unknown; however, evidence exists for an interplay between environmental and genetic factors. Several genes are involved in determining the disease susceptibility, at least one of them encoded within human leukocyte antigen gene complex. Other genomic regions coding for components of the immune system or myelin have also been suggested. Clinical, immunological and genetic data suggest that multiple sclerosis may turn out to be a heterogeneous disease. Therefore, molecular genetic dissection of this complex disease should provide important clues to its pathogenesis as well as unravel metabolic pathways for potential therapeutic or preventive strategies. This review will give an overview of recent progress and future challenges in identifying susceptibility genes for multiple sclerosis.

The HLA-Dw2 haplotype segregates closely with multiple sclerosis in multiplex families

Multiple sclerosis (MS) is associated with the HLA class II specificity Dw2, but the importance of its influence has been questioned, since sib-pair analysis has failed to show linkage with this haplotype. However, the use of 'identity by descent' (IBD) analysis may not be ideal, since it does not make use of the facts that (i) the Dw2-haplotype is the only haplotype with a confirmed role in MS, and (ii) it performs its influence in a dominant manner. We have investigated nine Swedish multiplex MS families. In eight of the families, the Dw2 haplotype occurred in MS patients. Within these families, Dw2 was shared by all 17 individuals with MS. In a compilation of 48 published multiplex MS families in which at least one patient carried Dw2, only three of 107 individuals with MS did not carry the Dw2 haplotype. This indicates that the Dw2 haplotype, when present in familial MS, may confer a stronger influence in MS susceptibility than generally recognized.

Epidemiologic evidence for multiple sclerosis as an infection

The worldwide distribution of multiple sclerosis (MS) can be described within three zones of frequency: high, medium, and low. The disease has a predilection for white races and for women. Migration studies show that changing residence changes MS risk. Studies of persons moving from high- to low-risk areas indicate that in the high-risk areas, MS is acquired by about age 15. Moves from low- to high-risk areas suggest that susceptibility is limited to persons between about ages 11 and 45. MS on the Faroe Islands has occurred as four successive epidemics beginning in 1943. The disease appears to have been introduced by British troops who occupied the islands for 5 years from 1940, and it has remained geographically localized within the Faroes for half a century. What was introduced must have been an infection, called the primary MS affection (PMSA), that was spread to and from successive cohorts of Faroese. In this concept, PMSA is a single widespread systemic infectious disease (perhaps asymptomatic) that only seldom leads to clinical neurologic MS. PMSA is also characterized by a need for prolonged exposure, limited age of susceptibility, and prolonged incubation. I believe that clinical MS is the rare late outcome of a specific, but unknown, infectious disease of adolescence and young adulthood and that this infection could well be caused by a thus-far-unidentified (retro)virus.

Genetic susceptibility to multiple sclerosis linked to myelin basic protein gene

Genetic factors have been implicated in the aetiology of multiple sclerosis (MS), but the genes conferring susceptibility to MS have not been identified. We carried out genetic linkage and association analyses by studying polymorphism of the myelin basic protein (MBP) gene on chromosome 18, a candidate gene for MS, in 21 MS families, 51 additional unrelated patients with definite MS, and 85 controls. All subjects were Finnish, and 14 of the families were from an area with an exceptional familial clustering of MS. Magnetic resonance imaging (MRI) was used to examine subclinical disease in symptom-free family members. In the association analysis, the allele frequencies between MS patients and controls differed significantly, p = 0.000049), the difference being attributable mainly to a higher frequency of a 1.27 kb allele among patients. In the linkage analysis, based on an autosomal dominant model and penetrance 0.05, a maximum LOD score of 3.42 (theta = 0.00) was obtained when patients with optic neuritis and their symptom-free siblings with abnormal MRI findings were classified as "affected". When these subjects were classified as "unknown" the maximum LOD scores ranged from 2.99 to 3.25 (theta = 0.00). The results suggest that in this population genetic predisposition to MS is closely linked to the MBP gene and that polymorphism at the MBP locus or an adjacent locus has a role in the aetiology of MS.

Discordance of T-cell receptor beta-chain genes in familial multiple sclerosis

Restriction fragment length polymorphisms of the T-cell receptor beta-chain gene were studied in DNA obtained from 96 individuals from 14 multiplex families with multiple sclerosis (MS). Thirty-four family members had definite MS and two had probable MS. Five normal family members had abnormal findings on cranial magnetic resonance imaging (MRI) scans. Linkage analysis was performed using the BglII and the KpnI polymorphisms. With penetrance values from 0.1 to 0.7, and altering the scoring of the normal individuals with abnormal findings on MRI scans from "unknown" to "affected," log of the odds scores between -4.59 to -12.76 were found for the autosomal dominant model. For the autosomal recessive model with a penetrance range from 0.1 to 1.0, the LOD scores ranged from -8.20 to -32.98. These findings do not support a direct role of T-cell receptor beta-chain gene in the inheritance of MS.

Positive autoradiographic findings in brains of four MS patients

Autoradiography of brain slices from 4 multiple sclerosis (MS) and 9 control patients was performed. After 6 weeks of exposure the exact picture of the white matter appeared on the X-ray films in all cases with MS, but only in one of the controls. The high level of autoradiographic signal from MS white matter suggests that an abnormal accumulation of radioactive trace elements takes place within the brains of MS victims.

Multiple sclerosis: an overview

Demyelinating lesions of MS are infiltrated by activated T-lymphocytes and macrophages with secretion of soluble factors. This results in the synthesis of oligoclonal immunoglobulin (IgG) by plasma cells. The activated T-lymphocytes migrate from the peripheral blood to the CNS. This hyperactive state is linked to a selective loss of the suppressor/inducer T-cell subset. Administration of a soluble factor--interferon gamma--enhances the immune response by promoting class II antigen expression on macrophages or astrocytes, resulting in a relapse. However, the reason for T-cell activation in peripheral blood is not known, nor is the antigen. Myelin basic protein (MBP) has been considered to be the target since MBP is able to induce chronic relapsing allergic encephalomyelitis (CRAE) in an animal model of MS. Yet other myelin antigens have succeeded in inducing CRAE in animal models, and anti-MBP antibodies have been found in healthy individuals. The possibility that the hyperimmune state results from a viral infection has not yet been proven. It is known that in Caucasians, a genetic susceptibility factor is linked to class II MHC. Using MRI it has been found that the presence of new plaques was not regularly correlated with relapses, which indicates that MS is an ongoing pathology process. Most drugs used in MS influence the immune response but have potential toxicity. Monoclonal antibodies offer the opportunity of specific targeting of T-cells and are promising for the future.

Lymphocytes subclasses and function in patients with optic neuritis in childhood with special reference to multiple sclerosis

Ten patients with childhood optic neuritis (5 with a single attack of ON and 5 with later MS) were studied at various stages of the disease. Lymphocyte count and function were analysed in the peripheral blood of all patients, 3 repeatedly, and in one they were also analysed in the CSF. T-lymphocytes counts were normal in all but 2 MS cases who had high counts. In acute stages the T4/T8 ratio were high in 1/3 determinations, in recovery low in 2/2 determinations, and in stable stages normal in 6/8 determinations. Lymphocyte function, measured by PHA, ConA and PWM stimulation, was normal in all but one. One patient showed significantly higher T-cell percentages and a high number of stimulated lymphocytes in CSF but a lower count of suppressor cells than in the blood. We found no abnormalities specific to MS nor to childhood MS or to disease activity stage. Rather than peripheral blood, it would seem more worthwhile to study CSF to clarify the pathogenesis of ON and MS.

Evoked potential testing in relatives of multiple sclerosis patients

Evoked potential (EP) tests were obtained in 110 neurologically normal first-degree relatives of patients with multiple sclerosis. Visual EP tests were performed in all relatives; brainstem auditory and median nerve somatosensory EP tests were performed in 67 relatives. The relatives had a mean visual EP P100 latency that was significantly longer than that for normal subjects controlled for age and gender. Asymmetries were seen in results from individual MS relatives, including interocular visual EP P100 differences of up to 14 ms, and interarm somatosensory Erb-N18 differences of up to 3.0 ms. We identified 19 pairs of patients and relatives who were HLA identical and 18 other pairs who were HLA double nonmatched. EP asymmetries were seen more often in the HLA identical siblings than in the HLA double patients, especially if they share HLA types with the patients. Since less than 2% of siblings of MS patients would be expected to eventually develop clinical MS, these small subclinical electrophysiological changes are not expected to be a sign of the future appearance of clinical MS. Clinicians should be aware not to overinterpret small EP changes in relatives of MS patients.

HLA and multiple sclerosis: population and families study

Association between HLA and multiple sclerosis (MS) was investigated at the population level on 100 MS patients genotyped for HLA-A, B, C, DR and Bf, Glo, and on 155 patients phenotyped for the same HLA antigens. Association between MS and DR2 was clearly confirmed, although its strength is rather weak. No other genetic marker could be related to the disease, no haplotype nor any allelic combination could be recognized as MS specific, and antigen genotype frequencies among the diseased could not ascertain the mode of inheritance, although dominance is very likely. Computer analysis between HLA, Bf, Glo and age of the patient, sex, age of onset and evolution of MS, impairment indexes, titres of anti-DNA and anti-measles antibodies in CSF did not show any interaction. Twenty sib pairs and two trios of MS were also studied; they showed no significant distortion with the random distribution of haplotypes. DR2 gene frequency, however, was significantly higher in sib pairs showing one or two haplotypes than in HLA different affected siblings. Three crossing-overs were identified which suggest where the HLA-linked MS susceptibility (MSS) gene could be located within the HLA segment, while other epistatic MSS genes or environmental factors are likely to be important.

A linkage analysis of the Gm locus and multiple sclerosis

We conducted linkage analyses of immunoglobulin G heavy chain marker (Gm) phenotypes and multiple sclerosis (MS) in 30 families, each having at least two first-degree relatives with definite/probable MS. These families yielded positive evidence for linkage to human leukocyte antigen (HLA) loci in previous analyses. In the present analysis, however, the results for Gm were negative. Most lod scores were negative, particularly at the smaller recombination values (theta). We explored the possibility of heterogeneity by subgrouping our data on the basis of specific HLA types (A3, B7) and Gm types (Gm1, Gm1,2) within the pedigrees. The results were again negative with no substantial differences in estimates of theta between subgroups.

HLA profiles in multiple sclerosis suggest two forms of disease and the existence of protective haplotypes

261 multiple sclerosis (MS) patients were HLA-A and -B typed and 94 were HLA-D typed. The results were compared to those of controls typed for HLA-A; HLA-B (356) and HLA-D (113). We confirm and extend earlier findings (Oger et al. 1980b) that some phenotypes could modulate the expression of the MS susceptibility gene linked to B7-DR2: DR3 was found together with DR2 in 12/94 MS and only 3/113 controls and could be marker for an "augmentor" gene. In contrast, B35 and DR1 as well as B12 and DR7 could be markers of protector genes. We compared typing results of patients subgrouped on clinical features. 61 patients with progressive evolution showed increased A1, A1-B8, B8-DR3 and A1-B8-DR3 when compared to 200 patients with remitting evolution. When compared to controls both groups showed increased B7 but only the remitting group showed increased DR2. 71 patients with "benign MS" showed increased B7-DR2 and A3-B7-DR2. 54 patients with "severe disease" showed increased DR3 and A1-B8-DR3 when compared to controls. Both groups showed increased B7 (49.2% and 44.4% versus 25.5% for controls). 120 patients treated greater than 5 years with azathioprine were divided into "no progression" and "progression" while treated. Both groups showed increased B7 when compared to controls. DR2 was increased only in the "no progression" group. B8-DR3 and A1-B8-DR3 were found increased in the "progression" group only. We conclude that two forms of MS exist with different HLA profiles.

HLA-D typing in multiple sclerosis: Israelis tested with European homozygous typing cells

The association of A3, B7, Dw2 and DR2 histocompatibility (HLA) markers with multiple sclerosis (MS) is well established among Northern Europeans and Caucasoids in the United States. We showed previously that A3 and B7 were not increased among Israelis with MS, and in a preliminary study Dw2 as well. An association of A3 and B7 is also lacking in Italians, Jordanian and Japanese MS patients. In Black American MS patients, the B7 frequency is slightly increased but Dw2 is still significantly associated with MS. For the HLA-DR antigen series DR2 is shown to have a stronger association to MS than A3 and B7. Conceivably, this antigen could be associated with MS even in populations where an association with A3 or B7 is lacking. Therefore, a study of HLA-A, B, C, DR and D antigens was carried out in Israel. No significant excess or deficiency of HLA antigens was found in MS. Possible explanations for these results are as follows: (1) the relevant HLA-D alleles in the Jewish population were not detected by the homozygous typing cells (HTCs) used, since they were derived primarily from European sources; (2) in contrast to the Caucasoid populations the genetic factor predisposing for MS is not associated with HLA alleles in the Israeli population; (3) MS is an heterogeneous disease and in Israelis, an environmental factor is sufficient to cause the disease.

HLA family studies and multiple sclerosis: A common gene, dominantly expressed

All available Australian families with more than one member suffering multiple sclerosis (MS) were HLA typed. As with all other individual published studies, convincing evidence for linkage between the HLA system and disease was not obtained. An analysis of 100 published affected sib-pairs and 17 cousin-pairs, however, established the existence of an HLA-linked disease susceptibility gene for MS, which is likely to be dominantly expressed. Dominance was also supported by the finding of only three HLA-DR2 (Dw2) homozygous individuals out of 60 unrelated patients which enabled rejection of a recessive gene hypothesis (p less than 0.02). Analysis of the sib-pair data strongly suggested that this MS gene is not rare in the normal population and may be as common as DR2.

Similar levels of immune complexes in cases of multiple sclerosis and their unaffected relatives

To investigate the possible effect of the hypothetical multiple sclerosis susceptibility (MSS) gene on circulating immune complexes, we employed a sensitive assay to test for the presence of immune complexes in sera of MS patients and unaffected relatives classified by the presence/absence of HLA-defined markers for the MSS gene. We found no significant differences between cases and relatives. The results suggest that elevated immune complex levels in MS patients' sera reported by others may not be unique to MS cases, but may represent instead a familial phenomenon. We also report a possible association between the A3 + B7 haplotype and increased immune complexes.

The significance of abnormal immune responses in patients with multiple sclerosis

Early diagnosis of multiple sclerosis (MS) may be assisted by tests for the abnormal immune responses of the central nervous system (CNS) including oligoclonal IgG bands in the cerebrospinal fluid (CSF), increased CNS IgG synthesis, increased CNS antibody synthesis against multiple viruses and increased numbers of enlarged lymphoid cells in the CSF. Alterations in immunological responses are important in the pathogenesis of MS. Further studies are needed, however, to identify the antigen(s) and/or antibodies responsible for oligoclonal IgG in the CSF of MS patients. Also, the cause(s) for the other immunological abnormalities with diagnostic importance need to be identified. The increased synthesis of antibodies against multiple unrelated viruses suggests generalized alteration in the immune regulatory system. The etiology of MS might be multifactorial involving abnormal immunological responses, possibly precipitated by infectious agents acquired during childhood by genetically susceptible individuals. The immunological responses including alterations in myelin basic protein concentration, antimyelin antibody and immune complex activities in CSF, and in vitro stimulation, suppression and migration inhibition of blood lymphocytes appear to correlate with stage of MS and severity of CNS damage. Some of the tests may become useful in estimating the prognosis of the disease. Longitudinal studies are needed to clarify the sensitivity of the diagnostic and prognostic immunological tests and etiological significance of these abnormalities in MS.

Relationship between measles HI titers and an MS susceptibility gene

Recently published studies of formal linkage analyses strongly suggest that a multiple sclerosis susceptibility (MSS) gene is linked to the HLA region of the sixth chromosome. The objective of this analysis was to investigate whether or not the gene has any demonstrable relationship to the immune status with regard to measles within members of multiple-case MS families. Family members were HLA-typed, and levels of antibodies to measles were determined using the hemagglutination inhibition assay. Since a specific, HLA-defined haplotype within each family is presumably a marker for the MSS gene, family members were characterized as either carrying [(+) controls] or not carrying [(-) controls] the MSS gene by the presence of this specific haplotype. Twenty families were entered into the analyses. Results revealed that the mean titer to measles was not different between (+) and (-) controls, and that MS cases had significantly higher titers than both control groups combined.

Genetic susceptibility to multiple sclerosis: a linkage analysis with age-of-onset corrections

To test the hypothesis that a multiple sclerosis susceptibility (MSS) gene is linked to the HLA loci, formal linkage analysis was conducted on 40 multiplex families, 20 each from the Seattle and Los Angeles areas. The computer program LIPED was utilized. A dominant model of inheritance was assumed. Penetrance values of 0.05, 0.35, and 0.67 were entered into the analyses, and an age-of-onset correction was incorporated. The resulting lod scores were supportive of linkage at the lower penetrance levels. The maximum lod score, 2.411, at an estimated recombination fraction of 0.10 in both males and females, was generated at a penetrance value of 0.05. With a penetrance value of 0.67, the lod scores did not support linkage. Under an autosomal dominant model of inheritance, the results were supportive of linkage when the presumed penetrance of the MSS gene is low. The results also confirmed the importance of incorporating an age-of-onset correction into linkage analyses.