Multiple sclerosis in the two northernmost counties of Norway

Systematic literature review and meta-analysis of the prevalence of secondary progressive multiple sclerosis in the USA, Europe, Canada, Australia, and Brazil

Background

Secondary progressive multiple sclerosis (SPMS) is a subtype of multiple sclerosis (MS), which is a chronic neurological disease, characterised by inflammation of the central nervous system. Most of MS patients eventually progress to SPMS. This study estimates the prevalence of SPMS in the United States of America, Europe, Canada, Australia, and Brazil.

Methods

A systematic literature search of the Medline and Embase databases was performed using the OVID™ SP platform to identify MS epidemiological studies published in English from database inception to September 22, 2020. Studies reporting the prevalence of MS and proportion of SPMS patients in the included population were selected. The pooled prevalence of SPMS was calculated based on the proportion of SPMS patients. The Loney quality assessment checklist was used for quality grading. A meta-analysis of the proportions was conducted in RStudio.

Results

A total of 4754 articles were retrieved, and prevalence was calculated from 97 relevant studies. Overall, 86 medium- and high-quality studies were included in the meta-analysis. Most studies were conducted in European countries (84 studies). The estimated pooled prevalence of SPMS was 22.42 (99% confidence interval: 18.30, 26.95)/100,000. The prevalence of SPMS was more in the North European countries, highest in Sweden and lowest in Brazil. A decline in SPMS prevalence was observed since the availability of oral disease-modifying therapies. We also observed a regional variation of higher SPMS prevalence in urban areas compared with rural areas.

Conclusion

High variability was observed in the estimated SPMS prevalence, and the quality of the studies conducted. The influence of latitude and other factors known to affect overall MS prevalence did not fully explain the wide range of inter-country and intra-country variability identified in the results.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12883-022-02820-0.

Time trends in the incidence and prevalence of multiple sclerosis in Norway during eight decades

Norway has been subjected to numerous epidemiological investigations on the prevalence and incidence of multiple sclerosis (MS), dating back to 1935. The objective of this study was to review the studies on the prevalence and incidence of MS in Norway, provide an update on the prevalence of MS in Norway, and describe the time trends in the prevalence and incidence of MS in relation to risk factors, case ascertainment, and data. We performed a systematic search on PubMed and MEDLINE up to November 2014 using the search string ‘multiple sclerosis prevalence in Norway’ or ‘multiple sclerosis incidence in Norway’. In addition, we scrutinized the reference lists of the publications identified for relevant citations. We retrieved data on the distribution of MS in Norway on December 31, 2013 from the Norwegian Multiple Sclerosis Registry and Biobank and the Norwegian Patient Registry. We identified 29 articles. From 1961 to 2014, the reported prevalence of MS increased from 20 to 203 per 100,000 inhabitants, and the incidence increased from 1.9 to 8.0 per 100,000. The nationwide crude prevalence in Norway, based on the Norwegian Patient Registry, was 208 per 100,000 on December 31, 2013. The reported prevalence of MS in Norway has increased 10-fold, with several possible causes. During eight decades, neurological health services have generally become more accessible to the population, and transforming diagnostic criteria has made the diagnosis of MS more precise and valid. There have also been changes in lifestyle behavior and known risk factors, such as vitamin D and smoking, that might have contributed to the increased incidence of MS. A possible role of increased survival in MS needs to be examined further.

This article is commented on by Berg-Hansen et al, published in 132: 364–367 (DOI: 10.1111/ane.12489).

Incidence and prevalence of multiple sclerosis in Norway

The incidence and prevalence of multiple sclerosis in several Norwegian counties have been assessed in a number of epidemiological studies since the first nationwide study covering the period from 1935 to 1948. Although the observations are not continuous, a large increase in incidence and prevalence is reported in these studies. The most remarkable incline has taken place in western and northern Norway. Parallel to the observed increase in occurrence of multiple sclerosis (MS), the Norwegian society has gone through notable changes from being a poor country immediately after World War II to an affluent, modern nation today. Thus, the healthcare system and neurological services have improved. Readily accessible services contribute to a quicker and better case ascertainment. Also, a lower threshold among the public to seek help for symptoms thought to originate in the CNS is probable. Environmental factors of possible biological importance in MS have also changed, for example diet, smoking habits and exposure to ultraviolet radiation, but the knowledge of change in these factors is so far mainly on the population level. To explore these questions, a comprehensive national MS registry combined with detailed information of assumed environmental risk factors operating in parallel in the society might be an important tool to further knowledge.

Prevalence and incidence of multiple sclerosis in Oppland County: a cross-sectional population-based study in a landlocked county of Eastern Norway

OBJECTIVES - We report the prevalence and incidence rates of multiple sclerosis (MS) in Oppland County, Norway. METHODS - Records from all patients diagnosed with MS at the two Oppland County hospitals, Gjøvik and Lillehammer during 1989-2001 were evaluated. In addition, all general practitioners in Oppland County reported their patients into the study. RESULTS - The age-adjusted prevalence rate of definite MS was 174.4/ 100 000 on the prevalence day 1 January 2002. When the probable cases were included, the prevalence rate rose to 185.6/100 000. The highest prevalence rates were detected in the northern mountain areas, thus corroborating the results from previous local surveys 30-50 years ago. The prevalence of MS was statistically significantly associated with climatic, socioeconomic and geographic variables in the county. The age-adjusted incidence of definite and probable MS in Oppland County was 6.6/100 000 during 1989-1993 increasing to 7.6/100 000 during 1994-1998. DISCUSSION - We found the highest prevalence rates of MS ever reported in Norway. Our findings indicate a possible influence of environmental factors.

Contribution of incidence to increasing prevalence of multiple sclerosis in Alberta, Canada

Alberta Health Care Insurance Plan (AHCIP) data were used to calculate prevalence and incidence rates for multiple sclerosis (MS) in the general population of Alberta from 1990 to 2004. Multiple sclerosis prevalence rose steadily each year over this time period, from 217.6/100,000 individuals in 1990 to 357.6/100,000 in 2004. Multiple sclerosis incidence fluctuated with a slight increase from 1990 to 2004, at 20.9/100,000 and 23.9/100,000, respectively. Age-specific prevalence rates were higher between ages 30 and 60 in 2004 than in 1990. The pattern of age-specific incidence rates was similar in 1990 and 2004, with a slight shift toward diagnosis in younger years. Gender-specific prevalence rates were higher for females in both 1990 and 2004, with a greater increase in females (43%) than males (29%). Gender-specific incidence rates were higher for females than males in both years, but there was no differential increase in incidence by gender from 1990 to 2004. The 2004 Alberta MS prevalence rate remains among the highest reported worldwide. Both increasing incidence and longer duration have likely contributed to increasing MS prevalence in the province.

Prevalence of multiple sclerosis in First Nations people of Alberta

BACKGROUND

Multiple Sclerosis (MS) is reported to be uncommon among North American aboriginals despite frequent intermarriage with people of European ancestry, but few population-based studies have been conducted. The purpose of this study was to determine the prevalence of MS among First Nations aboriginal people in Alberta, Canada compared to the general population.

METHODS

All hospital in-patient and physician fee-for-service records between 1994 and 2002 where a diagnosis of MS was mentioned were extracted from government health databases in the province of Alberta. First Nations people can be identified since the federal government (Health Canada) pays health care insurance premiums on their behalf. Multiple Sclerosis prevalence per 100,000 population for both First Nations people and the general population of Alberta were calculated for each year during this time span.

RESULTS

Among First Nations in Alberta, MS prevalence was 56.3 per 100,000 in 1994 and 99.9 per 100,000 in 2002, an increase of 43.6%. In 2002 prevalence was 158.1 and 38.0 for females and males respectively, a female to male ratio of 4.2:1. Multiple Sclerosis prevalence among the general population of Alberta was 262.6 per 100,000 in 1994 and 335.0 per 100,000 in 2002, an increase of 21.6%. In 2002 prevalence was 481.5 and 187.5 for females and males respectively, a female to male ratio of 2.6:1. Peak prevalence for both First Nations and general population females in 2002 was age 50-59, also 50-59 for both First Nations and general population males.

CONCLUSION

While MS prevalence in First Nations people is lower than in the general population of Alberta, it is not rare by worldwide standards.

Low frequency of the disease-associated DRB1*15-DQB1*06 haplotype may contribute to the low prevalence of multiple sclerosis in Sami

This study confirms a low frequency of multiple sclerosis (MS) among Sami. Only 12 Sami with a diagnosis of MS were identified in the Norwegian Sami population, which represents a significantly lower prevalence of MS in Sami (30/10(5)) compared with other Norwegians (73-164/10(5)). The clinical characteristics as well as the results of human leukocyte antigen (HLA)-DRB1 and -DQB1 typing of the Sami MS patients are reported, showing that three (27%) of the Sami MS patients carried the MS-associated HLA-DRB1*15-DQB1*06 haplotype. Interestingly, the DRB1*15-DQB1*06 haplotype had a significantly reduced frequency among Sami controls (0.086) compared with non-Sami Norwegian controls (0.163) (P(corrected) = 0.015). The low frequency of the disease-associated DRB1*15-DQB1*06 haplotype in the Sami population may contribute to the low prevalence of MS in Sami, in addition to other yet unidentified genetic and environmental factors.

Immunomodulatory treatment of multiple sclerosis in Norway

OBJECTIVES AND METHODS

National guidelines for immunomodulatory treatment in multiple sclerosis (MS) were established in Norway in 2001. However, the nation-wide treatment practice has not been evaluated since. We therefore obtained information of all patients who have received prescriptions for the approved immunomodulatory medications, interferon-beta (Betaferon, Avonex, Rebif) and glatiramer acetate (Copaxone) registered in the Norwegian Prescription Database (Reseptregisteret). We also made a survey of patients treated with mitoxantrone (Novantrone) as well as patients supplied with immunomodulatory drugs in treatment trials. To further calculate the treatment frequency, a nation-wide prevalence of MS in Norway was estimated, based on available prevalence studies.

RESULTS

The estimated frequency of MS was approximately 150/100,000 in southern Norway and 100/100,000 in northern Norway. The treatment frequencies varied from 15% to 47% between the different counties with a frequency of 28% for the whole country.

CONCLUSION

Substantial differences in treatment frequencies between counties were detected, reflecting major differences in clinical practice within the country. This calls for increased focus on clinical application of the established treatment guidelines.

Genetics in multiple sclerosis: past and future perspectives

The enormous development in the field of molecular genetics during the last decades has lead to optimism concerning the possibilities for identifying the causes of multiple sclerosis (MS) through genetic studies. However, we have learned that dense mapping of large sample sets is needed, which only can be achieved through large collaborative studies. The contribution from each yet unidentified gene is probably weaker than that of the well established human leukocyte antigen association. The ultimate goal of the search for susceptibility genes in MS is to develop diagnostic tools and better treatments that can prevent or reduce the development of symptoms of this often devastating disease.

Ethnic variation of Fc gamma receptor polymorphism in Sami and Norwegian populations

Receptors for the Fc domain of IgG (Fc gammaR) play a critical role in linking cellular and humoral immunity. The various Fc gammaR genotypes may contribute to differences in infectious and immune-related diseases in various ethnic populations. The Samis are the aboriginal inhabitants of Norway and Fennoscandinavia and differ ethnically from the Norwegians. The distribution of various immune-related diseases has been reported to differ between Sami and Norwegians. This is the first study to evaluate the distribution of Fc gammaR polymorphisms in a Sami population. Two hundred Samis were genotyped for polymorphisms in the Fc gammaRIIA, Fc gammaRIIIA and Fc gammaRIIIB genes. The genotype and allele frequencies were compared with those of 272 healthy Norwegians. The Sami and Norwegian Fc gammaRIIA, Fc gammaRIIIA and Fc gammaRIIIB genotypes differed significantly. The Samis had higher frequencies of the Fc gammaRIIa-H/H131, Fc gammaRIIIa-F/F158 and Fc gammaRIIIb-NA1/NA1 genotypes. The Fc gammaR genotypes were non-randomly distributed in both populations. These findings may be important for the prevalence of autoimmune and infectious diseases in the two populations.

Ethnic Variations of IL-10 Polymorphisms in a Sami and Norwegian Population

Interleukin-10 (IL-10) production is genetically determined and influenced by different polymorphisms in the promoter region of IL-10. These polymorphisms may contribute to the risk and clinical outcome of various infectious and immunological-related diseases. The Samis are the aboriginal inhabitants of Norway and Fennoscandinavia and are ethnically different from the Norwegians. Different distribution of various immune-related diseases among the Samis compared with Norwegians have been reported. This is the first study to evaluate the distribution of IL-10 polymorphisms in the Sami population. Two hundred healthy Samis were genotyped for polymorphisms in the promoter region of IL-10 at region -1082 (G/A), -819 (T/C) and -592 (A/C). The allele frequencies, genotypes and haplotypes were compared with 187 healthy Norwegians. A significantly higher number of the Samis than the Norwegians had the ATA/ATA genotype, whereas the Norwegians displayed a higher frequency of the GCC/GCC genotype (P=0.0057). There was a significant difference in haplotypes in the two populations with a P=0.0024. These findings may be important for the distribution and clinical outcome of various infectious and immune-related disorders in the two populations.

Mortality of Multiple Sclerosis in Spain: Demonstration of a North-South Gradient

OBJECTIVE

To analyse the geographical distribution of multiple sclerosis in Spain from 1975 to 1998.

METHODS

Age-adjusted mortality rates by province were obtained by the indirect method using the whole Spanish population as the reference. Then, standardised mortality ratios (SMRs) and their 95% confidence intervals were estimated.

RESULTS

For both men and women, provinces with SMRs higher than the mean tended to be in the northern third of Spain, whilst those with SMRs lower than the mean were mostly located in the southern half. A linear regression analysis showed a significant positive association between mortality and latitude.

CONCLUSION

A north-south gradient in age-adjusted multiple sclerosis mortality exists in Spain.

Multiple sclerosis in Nord-Trøndelag County, Norway: a prevalence and incidence study

OBJECTIVE

To calculate the prevalence and incidence of multiple sclerosis (MS) in Nord-Trøndelag County, Norway.

MATERIAL AND METHODS

The study comprised everyone diagnosed with MS according to the Poser criteria. On 1 January 2000 a total of 208 were identified: 130 women (62.5%) and 78 men (37.5%). We calculated the crude and age-adjusted annual incidence rates from 1974 to 1999.

RESULTS

The prevalence on 1 January 2000 was 163.6 of 100,000, 204.8 of 100,000 for women and 122.6 of 100,000 for men. The age-adjusted annual incidence increased from 3.9 to 5.6 per 100,000 from 1974 to 1999; women from 4.6 to 6.3 and men from 2.2 to 4.4. After 1984, the incidence among women increased most, peaking at 10.2 per 100,000 in 1984-88.

CONCLUSIONS

MS incidence is increasing in Nord-Trøndelag County. The prevalence is among the highest ever in Norway.

Phosphate depletion is the link between growth, stress and diet in the aetiology of MS

Predisposition to multiple sclerosis (MS) can originate in adolescence, when nutrient requirement is high and not satisfied and because of too little food intake and/or a poor diet. Growth per se increases the need for phosphate, an often neglected mineral in clinical conditions. The combination of marginal nutrition (either under- or malnutrition) with a negative phosphate balance, physical exertion, infections or other types of stress during puberty can disturb metabolism and result in demyelinization. Phosphate depletion (PD) can lead to neurological complications, which have been characterized in experimental and clinical studies. Hypophosphataemia, whether acute or chronic, induced by stress from accident, surgery or burns, by infection and/or undernutrition, is therefore an important etiological factor. Low SP levels have been reported in MS patients and the hypothesis that PD causes MS is presented here.

Increasing frequency of multiple sclerosis in Padova, Italy: a 30 year epidemiological survey

OBJECTIVE

To determine the incidence and prevalence rates of multiple sclerosis (MS) and their temporal profiles over the last 30 years in the province of Padova (northeast Italy).

BACKGROUND

In the early 1970s an epidemiological survey in the province of Padova showed a MS prevalence and incidence of 16/100 000 and 0.9/100 000 population, respectively; these figures are much lower than current estimates in other regions of Italy and Central Europe.

METHODS

The population of the study area was approximately 820 000 (422 028 women, 398 290 men) in the 1991 census. All possible sources of case collection were used, but only clinically definite/probable and laboratory-supported definite/probable MS were considered in the analysis of incidence and prevalence trends from 1971 to 1999.

RESULTS

On 31 December 1999, the crude prevalence rate was 80.5/100 000 (95% CI 70.3-90.7); prevalence was higher in women (111.1/100 000; 95% CI 99.0-123.1) than in men (49.7/100 000; 95% CI 41.3-58.1). This difference was significant (F/M = 2.43; z = 10.1, P < 0,00001); a rate adjusted for the European population was 81.4/100 000. On 31 December 1980 and on 31 December 1990 the estimated prevalence rates were 18/100 000 and 45.7/100 000, respectively. Thus, a fivefold increase in prevalence was observed from the 1970s. The mean annual incidence was 2.2/100 000 in the period 1980-89, 3.9 in the period 1990-94 and 4.2 in the period 1995 99. Thus, incidence increased more than fourfold from the 1970s through 1994 and remained quite stable in the last several years. Mean age at onset was 31.3 +/- 9.88 years. Mean diagnostic latency decreased significantly from 49.2 +/- 44.5 months in 1985 to 23.0 +/- 30.3 months in 1990, 12.9 +/- 15.61 in 1995 and 5.3 +/- 4.7 in 1999.

CONCLUSIONS

The actual prevalence (80.5/100 000) and incidence (4.2/100 000) of MS in the province of Padova agree with the most recent epidemiological estimates/trends observed in other Italian and European areas, except for Sardinia and Scotland. The increase in both incidence and prevalence rates observed in much of this region over the last 30 years parallels the introduction of more sensitive diagnostic techniques and a highly significant decrease in diagnostic latency. These findings probably do not support a real increase in the frequency of MS in northeast Italy because recent estimates of incidence have increased only slightly (3.9 to 4.2, which is < 10% in five years) and increase in the prevalence rate was almost completely due to the accumulation of new incidence cases.

Multiple sclerosis in Oslo, Norway: prevalence on 1 January 1995 and incidence over a 25-year period

The Oslo Multiple Sclerosis (MS) Registry was established in 1990, and this is the first report on the prevalence and incidence of MS in the city of Oslo, Norway. The prevalence rate of definite MS on 1 January 1995 was 120.4/10(5). Inclusion of patients of native Norwegian ancestry only and exclusion of non-Norwegian immigrants yielded a prevalence rate of 136.0/10(5). A similar prevalence rate (136.5/10(5)) was found when patients and immigrants from the other Nordic countries (Finland, Sweden, Denmark) were included. Segregation of the native Norwegian patients according to the counties where they were born showed no significant differences except for a disproportionate increase of patients born in the inland county of Oppland. A total of 794 cases were resident in Oslo at the time of a diagnosis of definite MS in the period 1972-99. The crude average annual incidence rate for each 5-year period, between 1972 and 1996, increased significantly from 3.7/10(5) in the 1972-76 to 8.7/10(5) in the 1992-96 period. The increase was more marked in relapsing-remitting (RR) than in primary progressive disease and in female cases.

The genetics of multiple sclerosis. A review

Multiple sclerosis (MS) is characterized by chronic inflammation and demyelination in the central nervous system (CNS). Although the etiology of MS is unknown, both genetic and environmental contributions to the pathogenesis are inferred from epidemiologic studies. Geographic distributions and epidemics of MS and data from migration studies provide evidence for some, thus far unidentified, environmental effects. The co-occurrence of MS with high and low frequencies in ethnic groups often sharing an environment, the increased recurrence rate in families, and the high concordance rate among identical twins point to inheritable determinants of susceptibility. Based on the autoimmune hypothesis of demyelination, genetic studies sought associations between MS and polymorphic alleles of candidate genes which regulate either the immune response or myelin production. The most consistent finding in case-control studies was the association with the major histocompatibility complex (MHC) (also called human leukocyte antigen--HLA) class II, DR15, DQ6, Dw2 haplotype. Studies on other gene products encoded within or close to the MHC complex on chromosome 6p21.3 (e.g., HLA DP, complement components, transporter proteins, tumor necrosis factor, and myelin-oligodendrocyte glycoprotein) resulted in conflicting observations in different patient populations. The potential contribution of polymorphic alleles within the genes of the T-cell receptor alpha beta chains, immunoglobulins, cytokines, and oligodendrocyte growth factors or their receptors to MS susceptibility either remains equivocal or is rejected. Studies on families with multiple affected members have revealed that MS is a complex trait, that the contribution of individual genes to susceptibility is probably small, and that differences are possible between familial and sporadic forms. The development of molecular and computer technologies have facilitated the performance of comprehensive genomic scans in multiplex families, which have confirmed the possible linkage of multiple loci to susceptibility, each with a minor contribution. Several provisional sites were reported, but only 6p21 (MHC complex), 5p14, and 17q22 were positive in more than one study. The British update demonstrated segregation among regions of interest depending on DR15 sharing, and excluded a gene of major effect from 95%, and one with a moderate effect from 65% of the genome. The extended study by the US collaboration group revealed that the MHC linkage was limited to families segregating HLA DR2 alleles, which suggested that linkage to the MHC is related to the HLA DR2 association, and that sporadic and familial MS share at least one common susceptibility marker. Further identification of MS susceptibility loci may involve additional family sets, more polymorphic markers, and the exploration of telomeric chromosomal regions. Data from these studies may further elucidate pathogenic mechanisms of MS.

Update on management and genetics of multiple sclerosis

Although the exact etiology of multiple sclerosis (MS) remains uncertain, there is an increasing body of evidence to support the role of genetic factors in MS susceptibility in general and the familial aggregation of MS in particular. MS.management continues to be largely symptom-specific. MS relapses are now frequently treated with IV-methylprednisone. In recent years, MS treatment trials are being conducted throughout the world. Interferon beta-1b has been approved as the first ongoing therapy for relapsing/remitting MS, although some issues/concerns remain to be addressed. In summary, while much research is still needed, important progress is being made in unravelling the etiology of MS and in developing management protocols which are not symptom- or relapse-specific.

Evidence for genetic basis of multiple sclerosis. The Canadian Collaborative Study Group

BACKGROUND Increased familial risks in multiple sclerosis (MS) range from 300-fold for monozygotic twins to 20-40-fold for biological first-degree relatives, suggesting a genetic influence. Yet if one identical twin has MS the other usually will not. One way of sorting out the contributions of genes and environment is to study half-sibs. METHODS In a Canadian population-based sample of 16 000 MS cases seen at 14 regional MS clinics one half-sib (or more) was reported by 939 index cases. By interview we elicited information on family structure and an illness in half-sibs and any full brothers or sisters. FINDINGS The age-adjusted MS rate in the 1839 half-sibs of these index cases was 1.32 percent compared with 3.46 percent for the 1395 full sibs of the same cases (p<0.001; likelihood ratio test). There were no significant differences in risk for maternal versus paternal half-sibs (1.42 percent vs 1.19 percent) or for those raised together versus those raised apart from the index case (1.17 percent vs 1.47 percent). INTERPRETATION Besides demonstrating the power and the feasibility of using half-sib studies to throw light on the aetiology of complex disorders, our findings show that a shared environment does not account for familial risk in MS and that maternal effects (such as intrauterine and perinatal factors, breastfeeding, and genomic imprinting) have no demonstrable effect on familial risk. Halving the number of potentially contributory genes (by comparing full-sib and half-sib rates) lowers the risk of MS by a factor of 2.62, an observation consistent with a polygenic hypothesis.

Epidemiology of multiple sclerosis

The inhomogeneous distribution of MS may represent an important clue about the cause of the disease. The prevalence of MS appears to be increasing in many regions of the world, although it is likely that in a majority of regions surveyed, this increase is attributable to differences in ascertainment over the relatively short period that MS has been surveyed worldwide, which is almost exclusively the last 50 years. MS occurs most frequently in regions populated by northern Europeans, and in these areas, it is much more common in the northern European population than in the indigenous populations. MS occurs in relatives of MS patients at a rate 10- to 50-fold greater than in the general population. On average, the absolute risk to a first-degree relative of an MS patient is 2% to 5%, depending on the exact degree of relatedness. Although the mode of transmission is not certain, a multigenic pattern best fits the observed pattern of transmission. A majority of monozygotic twins are discordant for MS, indicating that a major component of MS susceptibility is environmentally determined, although recent observations in adopted relatives suggest that this risk is not transmissible. Rare epidemics of MS involving small numbers of individuals in geographically isolated regions have been reported. A number of migrant studies suggest that the risk of acquiring MS may be altered by migration, although some also support genetic factors. Analytic approaches to address the role of various risk factors include ecologic studies, case-control studies, and cohort studies. Ecologic studies are best suited for addressing risk factors that influence overall population risk, whereas case-control studies are best suited for addressing risk factors that pertain to individuals within a population. If a risk factor is distributed homogeneously in a given population, a case-control study is insensitive to its effect. Improved methodology to diminish the biases inherent in case-control studies and identification of other important risk factors from basic scientific studies undoubtedly will be important for analytic epidemiologic studies of the future. Furthermore, analysis of highly informative populations, such as discordant identical twins and adoptive siblings of MS patients, likely will improve the specificity of case-control studies by minimizing the vast number of potential differences between cases and controls.

The role of mast cells and diet in the onset and maintenance of multiple sclerosis: a hypothesis

Mast cells may invade the brain as a consequence of a childhood infection or predisposition, and it is proposed that multiple sclerosis arises due to the effect of various mediators (histamine and protease) released from the perivascular mast cells after stimulation by some diet factor.

Is sporadic MS caused by an infection of adolescence and early adulthood? A case-control study of birth order position

Birth order position was examined in 164 cases with sporadic multiple sclerosis (MS), i.e. no other family members with MS, and spousal controls, matched for sibship size, socioeconomic status and opposite sex. The results did not find an association between birth order position and the subsequent development of MS and thus do not support the concept of an infectious cause for MS where "early exposure" is protective and exposure to the infection is a single event of short duration.

Descriptive epidemiology of multiple sclerosis in Europe in the 1980s: a critical overview

The oversimplified but commonly accepted belief, based on the comparison of the prevalence studies conducted until 1980, that the distribution of multiple sclerosis (MS) in Europe is related to latitude has been contradicted by a great number of prevalence and incidence studies carried out since 1980. The most recent studies, based on more appropriate methods, clearly indicate that the MS distribution in Europe is much more complex than supposed in the past. The MS distribution in Europe now appears to be very uneven, with great variations not only between areas at the same latitude, but also within the countries themselves. However, even the most recent European studies cannot be reliably compared because of differences in the denominator characteristics, case ascertainment accuracy, diagnostic criteria, and definitions of prevalence and incidence. Despite these problems, descriptive data since 1980 indicate that ethnicity plays an important role in determining the European MS distribution. Furthermore, variations in both prevalence and incidence rates in ethnically homogeneous populations confirm the i importance of environmental factors in determining the primary acquisition of the disease. Further descriptive studies based on more comparable methods and better control for ethnicity would more precisely define the role of genetic susceptibility as well as suggest more valuable clues regarding environmental factors affecting the primary acquisition of MS.

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.

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.

A possible paradox in the immunology of multiple sclerosis: its apparent lack of 'specificity' might provide clues to the etiology

As a further development from an earlier hypothesis, a pathogenic role of polyspecific natural, idiotypically connected antibodies is claimed, that recognize concomitantly a variety of CNS antigens and are matured to some degree to higher-affinity anti-CNS antibodies without ever losing their network association. On that basis, nitrophenol-carrier conjugates well-known to be foreign target antigens of natural antibodies and present in food commodities that have epidemiological links to MS, are considered as paradigmatic for agents of possible etiologic importance.

The prevalence of delayed and advanced sleep phase syndromes

To determine the prevalence of the delayed sleep phase syndrome (DSPS) and the contrasting advanced sleep phase syndrome (ASPS), a cross-sectional nationwide epidemiological study was performed in Norway. Screening questionnaires were sent to a random sample of 10,000 adult individuals (18-67 y), of both sexes, taken from the National register of Norway. The response rate was 77%. Diagnoses of DSPS and ASPS were based on International Classification of Sleep Disorders (ICSD) criteria. All individuals suspected of having DSPS or ASPS were requested to fill out a second questionnaire, and a sleep log for four weeks. Subjects for whom the suspicion of DSPS or ASPS could be upheld were contacted by telephone for a final confirmation. Of the 129 possible DSPS cases identified from the screening questionnaires, 17 (9 f; 8 m) remained with the confirmed diagnosis of DSPS. The prevalence was calculated to be 0.17% (95% Confidence Intervals: 0.10-0.28). Thirteen individuals had a mild to moderate DSPS and four had a severe DSPS. The mean age of onset was 15.4 y, and mean duration was 19.2 y. There was no significant correlation between prevalence and age. A sleep phase delay (MSPD) induced by social/environmental or psychological factors was found in 55 subjects (prevalence = 0.72%). Using strict ICSD criteria, no case of ASPS was detected, confirming earlier assumptions of the extreme rarity of this condition.

Multivariate analyses of factors associated with unemployment in people with multiple sclerosis

Variables at onset of multiple sclerosis (MS) as predictors of time to unemployment have been studied using multivariate survival (time-to-response) analyses. The study consisted of 79 patients with MS diagnosed in the two most northern counties of Norway between 1974-82. Diagnostic category, age at onset, sex, county, symptom groups, course of disease and occupation groups were identified as possible prognostic variables. Forty one patients (51%) were unemployed at last follow up. None of the 15 patients with probable or possible MS were unemployed due to MS. The multivariate analyses selected the nonremittent course or heavy physical work and age over 30 at onset as high risk factors associated with early unemployment.