Multiple sclerosis in the Orkney and Shetland Islands. III: Histocompatibility determinants

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.

Genome-wide homozygosity and multiple sclerosis in Orkney and Shetland Islanders

There is strong evidence for both genetic and environmental risk factors comprising the aetiology of multiple sclerosis (MS). While much progress has been made in recent years in identifying common genetic variants using genome-wide association studies, alternative approaches have remained relatively neglected. The prevalence of MS in Orkney and Shetland is among the highest in the world. Previous studies have suggested that a higher degree of parental relatedness in these isolated communities may contribute to the high rates of MS, indicating that recessive effects have an important role in MS aetiology. The Northern Isles Multiple Sclerosis (NIMS) study investigated the potential role of genome-wide homozygosity in MS risk by genotyping 88 MS patients, 89 controls matched by age, sex and ancestry, and a further 89 controls matched for sex and ancestry, but passed the majority of lifetime risk of developing MS (>70 years of age). Three participants were removed on the basis of pedigree-genomic anomalies (n=263). Three measures of genome-wide homozygosity were generated for each individual, and association with MS was assessed using logistic regression models. No effect of genome-wide homozygosity was detected, indicating that inbreeding and consanguinity are not risk factors for MS in this population.

Human leucocyte antigen class II polymorphism in Irish patients with multiple sclerosis

The contribution of human leucocyte antigen (HLA) to the genetic risk for multiple sclerosis (MS) in patients of Northern European Caucasoid ancestry has been known since the 1970s. The northern part of Ireland, including county Donegal, is known to be a high-risk area for the development of MS. Recorded prevalence rates for county Wexford in the south-east Ireland have been markedly lower and suggest the existence of a prevalence gradient within the island. To evaluate the association of HLA-DRB1 and -DQB1 haplotypes with MS in both Wexford and Donegal, we examined a total of 118 patients and 400 regionally matched controls. The aim of this exploratory study was to test the possibility of heterogeneity in HLA class II associations with MS and to identify potential predisposing or protective haplotypes, associated with MS risk in Ireland. We confirmed the association of DRB1*1501-DQB1*0602 haplotype carriage with MS in both Wexford [odds ratio (OR) = 2.95, P= 0.0020, P(cor)= 0.0220] and Donegal (OR = 2.29, P= 0.0030, P(cor)= 0.0420). A higher frequency and a significantly higher homozygosity rate of this haplotype in Donegal are likely contributing factors to the higher prevalence of MS in Donegal compared with Wexford. The distribution of HLA class II alleles among Irish MS patients and controls establishes that there is heterogeneity in HLA class II associations with MS within Ireland.

Identifying disease modifying genes in multiple sclerosis

Evidence is mounting that genetic variation influences not only susceptibility to multiple sclerosis (MS), but also its course and severity. Identification of disease modifying genes, however, poses unique challenges, especially on how to classify the course and outcome of the disease in ways that may be relevant to analysis of biological factors that might be influenced by genes. The power of the statistical approaches to detect small effects of individual genes in complex disorders such as MS is problematic, and approaches to estimate power must be appropriate for the data. Nonetheless, using contemporary schemes of classification, genetic variants that influence disease course have been found; in fact, a small number have been confirmed to influence disease course in two or more independent studies. This review addresses strategies relevant to identification of disease modifying genes in MS, and summarizes and critically evaluates the current state of knowledge in this area.

The role of genetic factors in multiple sclerosis susceptibility

There has been increasing evidence that genetic factors have a role in determining susceptibility to MS. Re-examination of results from prevalence and migration surveys reveals that there remains considerable ambiguity in interpretation. Some patterns previously thought to decisively support environmental determination may still be explained, at least in part, on a genetic basis. It seems inescapable that MS is probably due to an interaction of genetic and environmental factors. It remains undetermined whether or not genes exist which are truly necessary for the development of the disease. Existing data are consistent with the notion that the study of MS susceptibility will parallel the findings in experimental models of spontaneous autoimmunity and that at very least, two genes and almost certainly several genes will be found to influence susceptibility and interact in as yet unknown ways. One of these loci appears to be the Class II MHC, although its role may be minor at the germ line level. Roles for the T-cell receptor alpha and beta loci appear to be minor and may even be non-existent in contributing to heritable susceptibility. We predict that additional loci will be identified which influence both susceptibility and outcome and will be more important. Furthermore, it is clear that the understanding of the contribution of individual susceptibility loci will continue to be difficult because of the constraints of human pedigree data. It is likely that further resolution of the questions posed above related to genetic susceptibility in MS will require multicenter collaboration.

Multiple sclerosis in the Faroe Islands. VI. Studies of HLA markers

Occurrence of clinical neurologic multiple sclerosis (CNMS) among resident Faroese began between 1943 and 1973 and comprised three epidemics. The occupation by British forces for 5 years during World War II was interpreted to have been of major importance for the occurrence of these epidemics and led us to believe that CNMS is the rare, late result of a single, widespread, systemic and specific infectious disease which we have labelled the primary MS affection (PMSA). In this study we describe the occurrence of genetic markers of the HLA system in 16 Faroese MS patients, 25 of their siblings, 30 unrelated healthy neighbors and spouses to MS patients, 18 healthy controls from areas where no MS cases have been detected, and 80 unrelated normal Faroese. These studies show no significant deviations of HLA class I antigens, whereas the class II antigens do deviate: 50% of the Faroese MS patients carry the HLA-DR2 (DQ1/DRB 15) antigen, compared to a frequency of 15-20% among the control groups. Also the group of siblings of MS patients showed an increased frequency of DR4 (72%) compared to normal frequency among MS patients and other normal controls (43-47%). However, if DR15-positive individuals were excluded, this difference was further reduced. If PMSA was widespread within this group, DR4 or some closely associated genetic marker may confer protection against PMSA developing into CNMS. The occurrence of CNMS in these epidemics seems therefore associated to HLA class II-linked genetic factors similar to those found in studies of other caucasians with MS. This observation seems important in understanding the pathogenesis of this disease.

HLA and multiple sclerosis in Italy: a review of the literature

HLA antigens of locus A, C, B, DR and DQ were typed in 104 Italian multiple sclerosis patients and in 905 healthy controls; the results have been compared with those published in the Italian literature. The Italian studies have been reviewed regarding the ethnic origin of the typed population and the corresponding prevalence of the disease. The data suggest a lack of association between A3 and B7 antigens and Italian multiple sclerosis and a relevance of other DR locus antigens (mainly DR4 and DR5), in addition to DR2, in the susceptibility to the disease.

Class II HLA antigens in multiple sclerosis

HLA typing in Wellington revealed a stronger association of multiple sclerosis with DR2 than with DQw1. The association with DQw1 appeared to be due to linkage disequilibrium of this antigen with DR2. These results, when considered in conjunction with other studies, are most easily explained by the hypothesis that susceptibility to multiple sclerosis is influenced by multiple risk factors, with DR2 being an important risk factor in Caucasoid populations.

The distribution of multiple sclerosis in the United Kingdom

Parts of the United Kingdom have the highest incidence, prevalence and mortality rates for multiple sclerosis in the world. Although methods of ascertainment are not standardised, regional differences and changes with time are present for each of these statistics. Mortality has declined, whereas prevalence and hospital discharge rates have increased owing in part to the improved survival but also to better case ascertainment. The gradient in prevalence seen between Southern England (63/10(5)), Northern England and Northern Ireland (76-79/10(5)), Wales (c. 113/10(5)), North-East Scotland (155/10(5)) and the Orkneys (258/10(5)) can in part be attributed to varying methods of ascertainment but correlates with regional differences in the frequency of HLA-DR2 in normal individuals (21-50%). However no HLA-DR2 association is observed in parts of Scotland, where the prevalence is the highest in the United Kingdom, because HLA-DR2 and linked genes occur in up to 50% of the normal population from these areas. If the aetiology of multiple sclerosis is multifactorial the frequency of the disease will increase where susceptibility genes are common because the probability of concurrence of the remaining critical events is high; conversely when each aetiological agent is infrequent the chance of them all occurring in the same individual and therefore incidence of the disease are both lower. The fall in incidence observed in the Orkney Islands, possibly reflecting decline in an exogenous agent interacting with susceptibility factors, is consistent with this multifactorial hypothesis.

Immunoglobulin allotypes and susceptibility to multiple sclerosis. An epidemiological and genetic study in the Hautes-Pyrénées county of France

Serum samples collected from 69 patients with multiple sclerosis (MS) living in the Hautes-Pyrénées county were tested for immunoglobulin Gm gamma 1, gamma 2, and gamma 3, heavy chain allotypes (Gm system), and immunoglobulin light chain Kappa (Km system). A control group was made up of normal individuals living in the same county. We found a significant excess of individuals with Gm3; +/- 23;5/Gm3; +/- 23;5 amongst the MS patients as compared with controls (relative risk = 2.4). A slight increase of the Km (1) frequency was found in MS patients compared with controls, 21.7% vs 11.8%, but this difference was not significant.

The mystery of the origin of multiple sclerosis

Our present understanding of the aetiology and pathogenesis of multiple sclerosis is discussed in relation to the views of Sir William Gowers. He perceived that both environmental and genetic factors might be implicated in the aetiology of the disease. Evidence for the former was first reported in 1903, but has become convincing only in the past 20 years; the nature of the environmental factor remains obscure. Evidence for a genetic influence on susceptibility has accumulated since the 1930s, the most compelling coming from the recent Canadian twin study. The number and mode of operation of the genetic factors is still uncertain, but there is evidence for the implication of genetically controlled cellular immune mechanisms in the pathogenesis of the disease. The precise relationship between transient changes in immunological status and the development of new lesions has yet to be defined; magnetic resonance imaging (MRI) promises to play a significant role in this analysis because of its sensitivity in detecting abnormalities in multiple sclerosis. MRI is not in itself specific; it is probable that the similar appearances in multiple sclerosis and cerebral vascular disease both derive at least in part from the influence of astrocytic gliosis on proton content and distribution. The significance of the gliosis is uncertain. Gowers believed that the primary defect in multiple sclerosis lay in the astrocyte. Recent observations on the immunological functions of this cell in vitro suggest that it could be involved early in the pathogenesis of the lesion.

IgG (Gm) allotypes and multiple sclerosis in a French population: phenotype distribution and quantitative abnormalities in CSF with respect to sex, disease severity, and presence of intrathecal antibodies

The association of a given Gm allotype or phenotype with MS susceptibility, as previously described in some Caucasian populations, was not observed in a large French MS group, whether or not considering the possible influence of sex or disease severity. This result could be related to variations in geographical distribution of Gm alleles and MS susceptibility gene(s) or suggests the simultaneous involvement of Gm and other genetic system(s). In contrast, the corresponding CSFs exhibited already known MS-associated abnormalities of IgG1 (G1m) allotype contents, which therefore did not merely result from a Gm-associated MS susceptibility. These quantitative abnormalities were not sex dependent, but may fluctuate with MS severity. The G1m allotype levels in each CSF were not correlated with titers of various intrathecal antibodies but with the number of antibody specificities detected, a picture arguing for a polyclonal, non-antigen-specific activation of G1m allotype-producing B cells present in MS brain.

A review of the etiology of multiple sclerosis

The geographic distribution of multiple sclerosis and the influence of migration on the risk of contracting it point to an environmental factor as cause of the disease. This environmental factor might be a virus which might produce the demyelination process through an autoimmune reaction against components of the central nervous system. The other possible cause of multiple sclerosis is a genetic susceptibility, inferred from the higher risk for the disease found among relatives of patients with multiple sclerosis and on the association between the disease and some histocompatibility antigens of the HLA system. Both theories seem to be correct, with the environmental factors(s) causing multiple sclerosis only in the presence of a genetic susceptibility.

Multiple sclerosis: the present position

The advances of the past decade particularly in the application of evoked potential techniques and electrophoresis of CSF proteins have improved the accuracy of early diagnosis of multiple sclerosis. The geographical distribution of the disease, the effect of migration on prevalence, and the existence of clusters suggest that an environmental factor is involved in the aetiology; it is probably infective. Family and twin studies provide evidence for a genetic contribution which is probably multifactorial and related to immune regulation. The pathogenesis is at least in part immunologically mediated. A rational approach to therapy is difficult. In the present state of knowledge we are unlikely to be able to modify the course of multiple sclerosis by tackling a putative environmental agent. We are more likely to be able to do so by manipulating the pathogenesis, although an effective means of doing so has yet to be defined.

Power of the affected-sib-pair method to defect disease susceptibility loci of small effect: an application to multiple sclerosis

The distribution of marker locus identity-by-descent scores in affected sib pairs provides a powerful tool for detecting the presence of a linked non-Mendelian disease susceptibility locus. This basic approach is here extended to include a trio of sibs. A special type of sib trio consisting of two affected and one unaffected sib is investigated. It is shown that compared to affected-sib-pairs, trios with the above configuration are less efficient in detecting the presence of a linked disease susceptibility locus. When the generalized two-allele single locus model is fitted to sib pairs affected with multiple sclerosis, an estimate of the recombination fraction of 0.21 between the putative disease susceptibility locus and the HLA complex is obtained. However, this transmission model is deemed inadequate since a recombination fraction this large is inconsistent with the variety of HLA associations observed at the population level.

Multiple sclerosis in the Orkney and Shetland Islands. V: The effect on viral titres of histocompatibility determinants

HLA phenotypes were correlated with serum antibody titres to eight viruses in patients with multiple sclerosis and two matched control groups in the Orkney Islands. In patients, no specific HLA antigen was associated wtih increased or decreased viral titres. However, HLA-B7 was significantly correlated with higher measles titres in healthy controls. Furthermore, controls who had the HLA haplotypes, B7, DW2 ad B-cell 4, demonstrated significantly higher antibody titres to measles and rubella than controls without these determinants (P less than 0.005). To determine the effect of age, sex, and other variables upon viral titres, regression analysis was undertaken. A significant proportion of measles titre variance in patients was explained by sex and clinical factors. Among normal controls, HLA determinants explained a significant amount of measles and rubella titre variance. These data suggest that viral titres in normal individuals are influenced by certain HLA antigens and give indirect evidence that another, as yet undefined, determinant in the histocompatibility complex governs the immune response.