Selected reviews common childhood and adolescent infections and multiple sclerosis

Prevalence of multiple sclerosis: door-to-door survey in three rural areas of coastal Black Sea regions of Turkey

BACKGROUND

Little information exists on multiple sclerosis (MS) in Turkey. With a door-to-door survey in an urban part of Istanbul, we recently reported a prevalence rate of 101/100,000 population. We therefore investigated three rural areas of Turkey at the same latitude.

METHODS

The same survey methods were used for total populations of two rural areas (Kandıra and Geyve) near Istanbul, and for half the population of Erbaa, all near 40° north latitude on the Black Sea coast.

RESULTS

In Kandıra, 5 of 8 suspects were diagnosed as having MS among 8,171 screened, resulting in a prevalence rate of 61/100,000. Geyve with 7 MS cases in 17,016 screened had a prevalence of 41/100,000, and Erbaa with 15 MS cases in 28,177 screened one of 53/100,000. Together they showed a prevalence of 51/100,000. Of the 27 patients, 20 were women; 25 had definite and 2 possible MS, the former all with abnormal laboratory findings. Average ages were 30.5 years at onset and 39.1 years at diagnosis. Clinical features and course were typical of European MS.

CONCLUSION

These findings indicate that Turkey is a high-risk MS area, similar to most regions of Mediterranean Europe, where all recent increases are likely due to (undefined) environmental factors.

The ‘hygiene hypothesis’ and the development of multiple sclerosis

SUMMARY We review evidence linking inadequate microbial exposure in early life to the development of multiple sclerosis (MS). There is some supportive, but not conclusive evidence for a role of a hygienic environment in early life and MS. Population-level studies of MS are consistent with the hygiene hypothesis but are limited by methodological issues. Late infection with Epstein–Barr virus (EBV) has been prospectively associated with MS and must be incorporated into any model where the hygiene hypothesis is implicated in the development of MS. One possibility is that inadequate microbial exposure in early life contributes to a dysregulated host immune response to EBV. Two areas of particular interest include the potential role for helminthic infection in biasing the human immune response away from the immune profile associated with MS and also the role of microbial exposure in training the development of the EBV-specific immune response.

99th Dahlem conference on infection, inflammation and chronic inflammatory disorders: Epstein-Barr virus and multiple sclerosis: epidemiological evidence

While the causes of multiple sclerosis (MS) are unknown, there is strong evidence that infection with Epstein-Barr virus (EBV) is an important factor. In this review, we discuss the epidemiological evidence and argue for a causal role of EBV in MS aetiology. One of the most striking and consistent observations is that MS is extremely rare among EBV-negative individuals. Further, the timing of EBV infection appears to be critical, with individuals who are infected during adolescence and young adulthood, when the infection is more likely to manifest as mononucleosis, having a two- to threefold greater risk of MS compared to individuals infected in early life. These observations challenge the hygiene hypothesis which states that being in a high hygiene environment in early life increases future risk of MS - if this general formulation were true, EBV-negative individuals would be expected to have an increased risk of MS. Additional support for the causal role of EBV comes from longitudinal, prospective studies which show remarkable consistency, in that antibodies against EBV are elevated prior to MS onset. However, while infection with EBV is consistent with many observations of MS epidemiology, there are some that remain unexplained, suggesting that other factors are also involved in determining risk.

Epidemiology of Multiple Sclerosis

This chapter discusses the environmental factors associated to epidemiology of multiple sclerosis. The epidemiologic evidence points to three environ­mental risk factors—infection with the Epstein-Barr virus (EBV), low levels of vitamin D, and cigarette smoking—whose association with multiple sclerosis (MS) seems to satisfy in varying degrees most of the criteria that support causality, including temporality, strength, consis­tency, biologic gradient, and plausibility. None of these associations, however, has been tested experimentally in humans and only one––vitamin D deficiency is presently amenable to experimental interventions. The evidence, albeit more sparse and inconsistent, linking other environmental factors to MS risk are summarized. Epidemiologic clues to the hypothetical role of infection in MS are com­plex and often seem to point in opposite directions. The ecological studies, database/linkage analyses, and longitudinal studies of sunlight exposure and vitamin D are reviewed. Biologic mechanisms for smoking and increased risk of MS could be neuro­toxic, immunomodulatory, vascular, or they could involve increased frequency and duration of respiratory infections. Some other possible risk factors include––diet and hepatitis B vaccine.

The first case history of multiple sclerosis: Augustus d'Esté (1794-1848)

The personal diary of Sir Augustus d'Esté, born 1794 grandson of King George III of England, reveals a medical history strongly suggesting that Augustus suffered from multiple sclerosis (MS). It could well be the first record of a person having this disease. Charcot coined the term sclérose en plaques 20 years after the death of this patient in 1848. The onset of this man's MS seems to have been in 1822 with bilateral optic neuritis, the disease gradually developing in the classic manner with bouts derived from different loci in the central nervous system and eventually a secondary progressive form with paraparesis, sphincter incontinence, urinary problems and impotence. In 1941, Firth highlighted the case of Augustus d'Esté and later wrote a description of the pathology including a discussion on the aetiology of MS. No previous medical records have given such a characteristic picture of MS as this.

High prevalence of multiple sclerosis in the Swedish county of Värmland

Previous epidemiological studies have indicated that the county of Värmland in western Sweden may be a high-risk zone for multiple sclerosis (MS). The objective of this study was to determine the prevalence in the area. Hospital and general practice medical files were scrutinized. The diagnostic criteria of Poser were used, with 31 December 2002 as prevalence day. The prevalence was 170.07 per 100,000 inhabitants. The average annual incidence was 6.39 to 6.46 per 100,000 (1991—1995, 1996—2000). Multiple sclerosis was 2.3 times more common among women than men. There was a variation in prevalence among the 16 municipalities, however it was not statistically significant. The rates seemed highest in the southwestern part of the county, roughly similar in location to findings some 70 years earlier. When the prevalence ratios by geographical units for the county in 1933 were applied to the current prevalence, the distribution from these estimated cases differed from homogeneity with very high significance (p < 0.00001 ). In conclusion, this study supports previous reports indicating that Värmland continues to be a high-risk zone for MS and shares in the diffusion of the disease at the county level which we had presented for the country as a whole.

Potential risk factors for multiple sclerosis in Rio de Janeiro: a case-control study

PURPOSE: To evaluate potential risk factors for the development of multiple sclerosis in Brazilian patients. METHOD: A case control study was carried out in 81 patients enrolled at the Department of Neurology of the Hospital da Lagoa in Rio de Janeiro, and 81 paired controls. A standardized questionnaire on demographic, social and cultural variables, and medical and family history was used. Statistical analysis was performed using descriptive statistics and conditional logistic regression models with the SPSS for Windows software program. RESULTS: Having standard vaccinations (vaccinations specified by the Brazilian government) (OR=16.2; 95% CI=2.3-115.2), smoking (OR=7.6; 95% CI=2.1-28.2), being single (OR=4.7; 95% CI=1.4-15.6) and eating animal brain (OR=3.4; 95% CI=1.2-9.8) increased the risk of developing MS. CONCLUSIONS: RESULTS of this study may contribute towards better awareness of the epidemiological characteristics of Brazilian patients with multiple sclerosis.

Clinically observed chickenpox and the risk of childhood-onset multiple sclerosis

The authors conducted a population-based case-control study to investigate whether clinically observed chickenpox, linked with a level of intensity for clinical expression, increases the risk of multiple sclerosis (MS) in childhood. The cases were MS patients whose disease onset occurred between 1994 and 2003, before age 16 years, in France. Each case was matched for age, sex, and geographic origin with as many as 12 controls randomly selected from the general population. Information about clinically observed chickenpox in cases and controls before the index date regarding onset of MS was collected with a standardized questionnaire and was checked against health certificates. Conditional logistic regression was used to estimate the odds ratio for an association between MS and chickenpox. The 137 MS cases were matched with 1,061 controls. Clinically observed chickenpox had occurred in 76.6% of the cases and 84.9% of their matched controls. The adjusted odds ratio of MS onset associated with chickenpox occurrence was 0.58 (95% confidence interval: 0.36, 0.92). The authors concluded that clinically observed chickenpox was associated with a lower risk of childhood-onset MS in a French population.

Multiple sclerosis incidence in the era of measles-mumps-rubella mass vaccinations

BACKGROUND

Viral childhood infections may be involved in the multiple sclerosis (MS) pathogenesis. Following national Swedish vaccination programs, measles sharply declined in the 1970s, and measles, mumps, and rubella were virtually eliminated in cohorts born from 1981.

OBJECTIVES

To examine whether the vaccination induced reduction in these infections influences the MS incidence. In addition, the public health aspect justified an early evaluation of beneficial as well as harmful effects of mass vaccinations.

MATERIALS AND METHODS

From an incidence material of 534 MS patients, born 1959-1990, we selected one unvaccinated cohort and four cohorts, each corresponding to a vaccination program (MS patients = 251).

RESULTS

With the ability to detect a decrease by 30-35%, and an increase by 37-48% in the MS incidence in the first three cohorts, we found no vaccination related MS incidence changes. The background MS incidence showed a significant gradual age dependent increase.

CONCLUSIONS

While the present follow-up provided limited power in the last cohort, there is no evidence as yet that the radical decline in three viral infections influenced the MS incidence. However, the increasing background MS incidence of unknown cause may have concealed a reduction in MS risk associated with mass vaccinations.

Targeting myelin proteolipid protein to the MHC class I pathway by ubiquitination modulates the course of experimental autoimmune encephalomyelitis

Relapsing-remitting experimental autoimmune encephalomyelitis (EAE), a multiple sclerosis model, is induced in mice by injection of myelin proteolipid protein (PLP) encephalitogenic peptide, PLP139-151, in adjuvant. In this study, prior to EAE induction, mice were vaccinated with a bacterial plasmid encoding a PLP-ubiquitin fusion (pCMVUPLP). During the relapse phase of EAE, clinical signs, histopathologic changes, in vitro lymphoproliferation to PLP139-151 and interferon-gamma levels were reduced in pCMVUPLP-vaccinated mice, compared to mock-vaccinated mice (controls). Lymphocytes from pCMVUPLP-vaccinated mice produced interleukin-4, a cytokine lacking in controls. Thus, pCMVUPLP vaccination can modulate the relapse after EAE induction.

A case-control study of the environmental risk factors for narcolepsy

BACKGROUND

Despite the acknowledged importance of environmental risk factors in the etiology of narcolepsy, there is little research on this topic. This study sought to fill this gap in the literature and assess the risk of stressors and infectious diseases using a case-control study.

METHODS

Cases (n = 63) were recruited through the Stanford Center for Narcolepsy. All were HLA-DQB1*0602 positive, met conventional Multiple Sleep Latency Test criteria, and reported unambiguous cataplexy. Controls (n = 63) were nonrelated family members of cases and local community members. A self-administered questionnaire was used to assess the frequency and timing of possible risk factors.

RESULTS

Of the infectious diseases examined, only flu infections and unexplained fevers carried a significant risk. Several of the stressors carried a significant risk including a major change in sleeping habits. When the timing of all risk factors was considered, exposure prior to puberty increased the risk for developing narcolepsy.

CONCLUSIONS

These findings emphasize the importance of environmental risk factors in the etiology of narcolepsy. This highlights the need for further research on this aspect of narcolepsy so a complete understanding of a disorder that affects 1 in 2,000 individuals can emerge.

Environmental risk factors for multiple sclerosis. Part II: Noninfectious factors

As discussed in Part I of this review, the geographic distribution of multiple sclerosis (MS) and the change in risk among migrants provide compelling evidence for the existence of strong environmental determinants of MS, where "environmental" is broadly defined to include differences in diet and other behaviors. As we did for infections, we focus here primarily on those factors that may contribute to explain the geographic variations in MS prevalence and the change in risk among migrants. Among these, sunlight exposure emerges as being the most likely candidate. Because the effects of sun exposure may be mediated by vitamin D, we also examine the evidence linking vitamin D intake or status to MS risk. Furthermore, we review the evidence on cigarette smoking, which cannot explain the geographic variations in MS risk, but may contribute to the recently reported increases in the female/male ratio in MS incidence. Other proposed risk factors for MS are mentioned only briefly; although we recognize that some of these might be genuine, evidence is usually sparse and unpersuasive.

The risk for multiple sclerosis in female nurse anaesthetists: a register based study

BACKGROUND

Previous studies have suggested that exposure to organic solvents, including volatile anaesthetic agents, may be a risk factor for multiple sclerosis (MS), possibly in combination with genetic and other environmental factors.

AIMS

To further investigate the role of volatile anaesthetic agents having similar acute toxic effects to other organic solvents.

METHODS

Female nurse anaesthetists, other female nurses, and female teachers from middle and upper compulsory school levels were identified and retrieved from the 1985 census, Statistics Sweden. By means of the unique personal identity number in Sweden, these individuals were linked with the disability pension registers at The National Social Insurance Board and also with data on hospital care 1985-2000 at The National Board of Health and Welfare.

RESULTS

The cumulative incidence rate ratio of MS was found to be increased in female nurse anaesthetists in relation to other nurses (statistically not significant) and teachers (statistically significant), respectively.

CONCLUSIONS

These findings give some support to previous findings of an increased risk for MS in nurse anaesthetists. This is interesting in the context of previous observations of organic solvents in general as a potential risk factor in MS.

Divergent risk of multiple sclerosis in two anabaptist communities in America

A lowered risk of multiple sclerosis (MS) has been reported in the Hutterite community residing mainly in southern Canada. In another anabaptist community, the Old Colony Mennonites (OCM), settled in Canada and spread to Latin America, only a large pedigree with an increased risk of autoimmune diseases, including type I diabetes and three cases of MS, was reported. The prevalence of MS in the pedigree (3,158 per 100,000), even when observing its confidence interval, seems rather high, and the MS prevalence in the Mennonite general population is assumed at least to be equal to the Canadian rates. Based upon an extended study of the literature, the hypothesis that smoking and curing with nitrate/nitrite plays any role, by interaction with inflammatory intestinal changes in childhood infections, is supported. In addition, tobacco smoking and short-term breast-feeding as possible risk factors are also in line with a higher MS risk in OCM, whereas insecticides and herbicides can be excluded as risk factors in MS.

Further considerations on the distribution of multiple sclerosis in Sweden

OBJECTIVES

The geographic distribution of multiple sclerosis (MS) in Sweden over time was compared in order to analyze homogeneity.

METHODS

The distribution of MS was compared among three nationwide resources: 1301 hospital cases 1925-1934; 5425 deaths 1952-1992; and 11,371 disability pension recipients 1971-1994.

RESULTS

Distributions by county (lan) were markedly non-homogenous, with greatest variations in the early prevalence series (16-232% of the national mean), less within the death data (75-170%), and least for the disability series (87-128%). Maximal rates for MS in the early prevalence series were found for the cluster of seven counties surrounding the two major lakes of south central Sweden, as well as for one region on the northern shore of the Bay of Bothnia, and another also off the Bay north of Stockholm.

CONCLUSION

Though the epidemiologic sources are quite different, they are internally consistent and thus provide three consecutive cross-sectional views of the distribution over time. When considered together the data may be compatible with a thesis of the origin and spread of MS within Sweden from the south-central inland lake regions of the country. Such spread within a half century is too rapid for a genetic cause, including HLA patterns.

Environmental risk factors in multiple sclerosis aetiology

The epidemiology of multiple sclerosis (MS) has been intensively studied. It is conceptualised as a complex disease in which genetic and environmental factors act together to cause disease. There are temporal and geographic variations in disease risk, and risk of disease may be affected by migration between regions of differing risk. Numerous potential causal factors including infection, immunisations, physical and emotional stressors, climate, diet, and occupational exposures have been studied using various observational study designs. Thus far, no single environmental exposure has been consistently identified as a causal factor in MS, but sufficient data have accumulated that causal pathways should be postulated and tested. This review will focus on the environmental epidemiology of MS.

Childhood Infections as Risk Factors for Multiple Sclerosis: Belgrade Case-Control Study

The aim of this case-control study was to analyze the role of childhood infections and vaccinations in patients with MS in the Belgrade population. The study group comprised 110 cases with definite MS according to Poser's criteria, in whom onset symptoms occurred up to 2 years prior to the interview. An equal number of controls, individually matched by sex, age and area of residence, was recruited from patients with various nonautoimmune neurological disorders. Measles (OR = 2.6, 95%CI 1.4-5.0), chickenpox (OR = 3.0, 95%CI 1.5-6.0), rubella (OR = 2.4, 95%CI 1.2-4.7), whooping cough (OR = 1.9, 95%CI 0.8-4.4), and mumps (OR = 1.8, 95%CI 0.8-4.5), at age < or = 7 years, were more frequently reported by MS cases. The total number of childhood viral infections (including measles, rubella, chickenpox, and mumps) at age < or = 7 years was significantly higher in MS cases than in controls (OR = 1.8, 95%CI 1.4-2.5). Concerning vaccinations, no statistically significant differences were found between groups. According to multivariate analysis, rubella (OR = 2.5, 95%CI 1.4-4.4, p = 0.001) and measles (OR = 2.4, 95%CI 1.3-4.3, p = 0.003) at age < or = 7 years were significantly related to MS.

Multiple Sclerosis

This chapter provides information on the epidemiology of multiple sclerosis (MS), the most common disabling neurological disease in young adults. It describes the clinical and pathologic features of MS and how these features pose challenges for clinical diagnosis and case definition criteria. Information is provided regarding the descriptive epidemiology of MS, including studies of incidence, prevalence, and temporal trends in MS frequency. Also included is a discussion of the interesting geographical features of the MS distribution, including MS disease clusters, the latitude gradient in disease risk, and migrant studies of individuals who move from high-risk to low-risk regions. Other sections of the chapter cover evidence regarding the infectious etiology of MS, including the important role that Epstein-Barr virus appears to play in disease susceptibility. The role of lifestyle factors is receiving increasing emphasis in MS epidemiologic studies, and evidence is summarized regarding the potential role of cigarette smoking, diet, and hormonal factors.

Multiple sclerosis and Kaposi's sarcoma--chronic diseases associated with new human herpesviruses?

Two diseases that for many years have been suspected to be of viral origin are multiple sclerosis (MS) and Kaposi's sarcoma (KS). With the use of a new technique called representational difference analysis both these diseases have recently been associated with new lymphotropic herpesviruses, i.e. human herpesviruses (HHV) 6 and 8. HHV-6 is a ubiquitous virus and the etiological agent of exanthema subitum. Viral neuroinvasion occurs frequently in primary HHV-6 infection, and meningitis, encephalitis and demyelination have been described as rare complications. A relation with MS has been suggested for HHV-6, as the virus has been detected in MS plaques in the brain. Data from different studies are, however, conflicting and a definitive role for HHV-6 in MS pathogenesis has not been established. HHV-8 is believed to be the causative agent of KS, and is also associated with some rare hematological malignancies. The viral genome contains several potential oncogenes that are believed to have been picked up from the human genome during evolution. The role of HHV-8 in healthy, immunocompetent individuals is however uncertain. In conclusion, the full spectrum of human diseases associated with these new viruses is not yet understood, and rapid developments in molecular biology will continue to shed new light on the interactions between herpesviruses and their hosts.

Human immunodeficiency virus-1 infection and multiple sclerosis-like illness in a child

We present a child with human immune deficiency virus-1 infection associated with a multiple sclerosis-like illness. This case is the first reported of human immune deficiency virus-1 infection and a disease indistinguishable from multiple sclerosis in a child. Because of the rarity of either disease in pediatric patients, their coexistence in a child argues in favor of a casual association between the two illnesses, thus reinforcing the long-held assumption that viral agents may trigger some of the immunologic abnormalities underlying multiple sclerosis. Cases in which such an association was present in adults are also described in this article.

Prevalence of herpesvirus DNA in MS patients and healthy blood donors

OBJECTIVES

The aim of this study is to determine the DNA prevalence of different members of Herpesviridae in multiple sclerosis (MS) patients and to describe the possible effect of beta-interferon treatment on such prevalence.

MATERIAL AND METHODS

With a nested polymerase chain reaction (PCR) assay we have studied the DNA of the peripheral blood mononuclear cells (PBMCs) of 204 whole blood samples, [102 from patients with relapsing-remitting MS (RRMS), of which 62 were treated with beta-interferon, and 102 from healthy blood donors].

RESULTS

We only found a statistically significant difference for human herpesvirus type 6 (HHV-6) DNA prevalence (P < 0.0001): HHV-6 is 2.26 times more frequent in MS patients than in healthy donors. There was no difference in the HHV-6 prevalence between beta-interferon treated and untreated patients.

CONCLUSION

1. Among the herpesviruses, HHV-6 was the only one showing altered prevalence. This either indicates that HHV-6 is involved in the pathogenesis of MS, or it simply indicates that MS influences latency or reactivation of HHV-6 without any direct involvement of HHV-6 in the disease process of MS. 2. Treatment with beta-interferon does not make a difference on the DNA prevalence of the herpesviruses studied in our MS patients.

Nutrition and diet in the clinical management of multiple sclerosis

For many years, medical interest in the relationship between nutrition and multiple sclerosis (MS) has focused largely on aetiology and the influence of dietary fat on the rate and severity of disease. While the cause of MS remains unknown and the influence of dietary fat is unclear, recent studies on antioxidant intake and oxidative stress in MS are strengthening the rationale in support of a healthy eating regime following diagnosis. Dietary intake in MS and the influence of advanced disease on nutritional status are less well researched and documented. Both obesity and malnutrition may occur with detrimental consequences to functional abilities. Cognitive difficulties, dysphagia and the side-effects of drug treatment may further contribute to deterioration in nutritional status. This paper aims to provide a practical overview of dietary management in MS. It reviews the available evidence relating nutrition to MS and discusses dietary management, with particular emphasis on the identification and alleviation of factors affecting nutritional status.

A multiple sclerosis cluster associated with a small, north-central Illinois community

The authors investigated a reported incidence cluster of multiple sclerosis (MS) cases in a small, north-central Illinois community to determine validity and statistical significance. DePue, Illinois--a small, north-central Illinois community--has previously been the site of significant environmental heavy-metal exposure from a zinc smelter. Significant contamination of soil and water with zinc and other metals has been documented in this community during the time period of interest. In the mid-1990s, several cases of MS were reported to the Illinois Department of Public Health within the geographic limits of this community. Available medical records from purported MS cases reported to the Illinois Department of Public Health were reviewed, and living individuals were seen and examined. Statistical analyses were conducted with clinically definite MS cases; onset dates were determined by first symptom, and expected incidence rates were determined from published epidemiologic studies. Nine new cases of clinically definite MS occurred among residents of DePue, Illinois, during the period between 1971 and 1990. Seven of the 8 living subjects included in the final analyses were examined by one author (RS). The computed incidence rate deriving from these cases within DePue Township, Illinois, represented a statistically significant excess of new MS cases over expected. During the period from 1971 through 1990, a significant excess of MS cases occurred within the population of DePue, Illinois. Significant exposure of this population to mitogenic trace metals, including zinc, was also documented during this time period.

[Multiple sclerosis: pathogenesis and manifestations in children]

Multiple sclerosis (MS) is rare in children and occurs exceptionally before ten years. Sex ratio (girl/boy) is around 2.5 to 3, higher than in adults. Brain stem dysfunction and meningeal symptoms are more commonly first manifestations of the disease than in adults. Optic neuritis is also a frequent early manifestation. The etiology of the disease remains unclear and none of the advanced hypotheses (infectious, genetic, environmental) can by themselves explain its occurrence. There is a genetic susceptibility which is probably linked to many genes leading to a low related risk (less than two). A viral trigger mechanism in a person with a genetic predisposition is possible. New therapies result from a better understanding of the closed immune mechanisms of the disease.

Multiple sclerosis: genomic rewards

A large body of immunologic, epidemiologic, and genetic data indicate that tissue injury in multiple sclerosis (MS) results from an abnormal immune response to one or more myelin antigens that develops in genetically susceptible individuals after exposure to an as-yet undefined causal agent. The genetic component of MS etiology is believed to result from the action of several genes of moderate effect. The incomplete penetrance of MS susceptibility alleles probably reflects interactions with other genes, post transcriptional regulatory mechanisms, and significant nutritional and environmental influences. Equally significant, it is also likely that genetic heterogeneity exists, meaning that specific genes influence susceptibility and pathogenesis in some affects but not in others. Results in multiplex MS families confirm the genetic importance of the MHC region in conferring susceptibility of MS. Susceptibility may be mediated by the class II genes themselves (DR, DQ or both), related to the known function of these molecules in the normal immune response, e.g. antigen binding and presentation and T cell repertoire determination. The possibility that other genes in the MHC or the telomeric region of the MHC are responsible for the observed genetic effect cannot be excluded. The data also indicate that although the MHC region plays a significant role in MS susceptibility, much of the genetic effect in MS remains to be explained. Some loci may be involved in the initial pathogenic events, while others could influence the development and progression of the disease. The past few years have seen real progress in the development of laboratory and analytical approaches to study non-Mendelian complex genetic disorders and in defining the pathological basis of demyelination, setting the stage for the final characterization of the genes involved in MS susceptibility and pathogenesis. Their identification and characterization is likely to define the basic etiology of the disease, improve risk assessment and influence therapeutics.

Epstein-Barr virus and multiple sclerosis

It has been suggested that the Epstein-Barr virus (EBV) plays a role in the etiology of multiple sclerosis (MS), but individual epidemiologic studies have been inconclusive, in part because of the high prevalence of previous infection among individuals without MS. We conducted a systematic review of case-control studies comparing EBV serology in MS patients and controls. Eight published investigations were identified, including a total of 1,005 cases and 1,060 controls. The summary odds ratio of MS comparing EBV seropositive individuals with EBV seronegative individuals was 13.5 (95% CI = 6.3-31.4). The strength and consistency of this association and the high sensitivity and specificity of EBV serology suggest that these results are not readily explained by an aspecific immune activation among MS patients. These findings support a role of EBV in the etiology of MS.

The genetic epidemiology of multiple sclerosis

Epidemiological studies have implicated an interplay between genetic and environmental factors in the aetiology of multiple sclerosis (MS). There is a familial recurrence rate of approximately 15%. Meta-analysis of the recurrence risk shows that the rate is highest overall for siblings, then parents and children, with lower rates in second- and third-degree relatives. Recurrence is highest for monozygotic twins. Conversely, the frequency in adoptees is similar to the population lifetime risk. The age-adjusted risk for half siblings is also less than for full siblings. Recurrence is higher in the children of conjugal pairs with MS than the offspring of single affected. These classical genetic observations suggest that MS is a complex trait in which susceptibility is determined by several genes acting independently or epistatically. Comparisons between co-affected sibling pairs provide no evidence for correlation with age or year at onset and mode of presentation or disability. Thus far, the identification of susceptibility genes has proved elusive but genetic strategies are now in place which should illuminate the problem. The main dividend will be an improved understanding of the pathogenesis. To date, population studies have demonstrated an association between the class II major histocompatibility complex (MHC) alleles DR15 and DQ6 and their corresponding genotypes. An association with DR4, with or without the primary DR15 link, is seen in some Mediterranean populations. Candidate gene approaches have otherwise proved unrewarding. Four groups of investigators have undertaken a systematic search of the genome. In common with most other complex traits, no major susceptibility gene has been identified but regions of interest have been provisionally identified. These genetic analyses are predicated on the assumption that MS is one disease. Genotypic and phenotypic analyses are beginning to question this assumption. A major part of future studies in the genetics of MS will be to resolve the question of disease heterogeneity.