MS risk in immigrants in the McDonald era: A population-based study in Ontario, Canada

The misclassification of depression and anxiety disorders in the multiple sclerosis prodrome: A probabilistic bias analysis

BACKGROUND

Studies suggest that depression/anxiety form part of the multiple sclerosis (MS) prodrome. However, several biases have not been addressed. We re-examined this association after correcting for: (i) misclassification of individuals not seeking healthcare, (ii) differential surveillance of depression/anxiety in the health system, and (iii) misclassified person-time from using the date of the first MS-related diagnostic claim (i.e., a demyelinating event) as a proxy for MS onset.

METHODS

In this cohort study, we applied a validated algorithm to health administrative ('claims') data in British Columbia, Canada (1991-2020) to identify MS cases, and matched to general population controls. The neurologist-recorded date of MS symptom onset was available for a subset of the MS cases. We identified depression/anxiety in the 5-years preceding the first demyelinating claim using a validated algorithm. We compared the prevalence of depression/anxiety using modified Poisson regression. To account for misclassification and differential surveillance, we applied probabilistic bias analyses; for misclassified person-time, we applied time-distribution matching to the MS symptom onset date.

RESULTS

Our cohort included 9929 MS cases and 49,574 controls. The prevalence ratio for depression/anxiety was 1.74 (95 %CI: 1.66-1.81). Following correction for misclassification, differential surveillance using a detection ratio of 1.11, and misclassified person-time, the prevalence ratio increased to 3.25 (95 %CI: 1.98-40.54). When the same correction was conducted, but a detection ratio of 1.16 was applied, the prevalence ratio increased to 3.13 (95 %CI: 1.97-33.52).

CONCLUSIONS

Previous conventional analyses were biased towards the null, leading to an under-estimation of the association between depression/anxiety and MS in the prodromal period. This first application of probabilistic quantitative bias analysis within MS research demonstrates both its feasibility and utility.

Differential diagnosis of suspected multiple sclerosis: considerations in people from minority ethnic and racial backgrounds in North America, northern Europe, and Australasia

The differential diagnosis of suspected multiple sclerosis has been developed using data from North America, northern Europe, and Australasia, with a focus on White populations. People from minority ethnic and racial backgrounds in regions where prevalence of multiple sclerosis is high are more often negatively affected by social determinants of health, compared with White people in these regions. A better understanding of changing demographics, the clinical characteristics of people from minority ethnic or racial backgrounds, and the social challenges they face might facilitate equitable clinical approaches when considering a diagnosis of multiple sclerosis. Neuromyelitis optica, systemic lupus erythematous, neurosarcoidosis, infections, and cerebrovascular conditions (eg, hypertension) should be considered in the differential diagnosis of multiple sclerosis for people from minority ethnic and racial backgrounds in North America, northern Europe, and Australasia. The diagnosis of multiple sclerosis in people from a minority ethnic or racial background in these regions requires a comprehensive approach that considers the complex interplay of immigration, diagnostic inequity, and social determinants of health.

Multiple sclerosis: emerging epidemiological trends and redefining the clinical course

Multiple sclerosis is a chronic, inflammatory, and neurodegenerative disease of the central nervous system and a major cause of neurological disability in young adults. Its prevalence and incidence are increasing, and it has been estimated at over 2.8 million cases worldwide, in addition to recent trends towards a shift in MS prevalence to older ages, with peak prevalence estimates in the sixth decade of life. Although historically the relapsing and progressive phases of the disease have been considered separate clinical entities, recent evidence of progression independent of relapse activity (PIRA) has led to a reconsideration of multiple sclerosis as a continuum, in which relapsing and progressive features variably coexist from the earliest stages of the disease, challenging the traditional view of the disease course. In this Series article, we provide an overview of how the traditional description of the clinical course of MS and epidemiological trends in Europe have evolved. For this purpose, we focus on the concept of PIRA, discussing its potential as the main mechanism by which patients acquire disability, how its definition varies between studies, and ongoing research in this field. We emphasise the importance of incorporating the assessment of hidden clinical manifestations into patient management to help uncover and quantify the PIRA phenomenon and the possible implications for future changes in the clinical classification of the disease. At the same time, we provide insights into overcoming the challenges of identifying and defining PIRA and adopting a new understanding of the clinical course of MS.

The overall and smoking-attributable burden of multiple sclerosis among older adults aged 65-89 years from 1990 to 2019 and predictions to 2040

Background

The global prevalence of aging individuals with multiple sclerosis (MS) is increasing. This study aimed to assess the burden and trends of overall and smoking-attributable MS in older adults aged 65-89 years at the global, regional, and national levels.

Methods

The number and rates of years of life lived with disability (YLD) and years of life lost (YLL) due to MS for older adults in 204 countries and territories from 1990 to 2019 were retrieved from the Global Burden of Disease (GBD) Study 2019. Estimated annual percentage change (EAPC) in the age-standardized YLD and YLL rates were calculated to quantify the temporal trends. The Bayesian age-period-cohort model was used to predict the trends from 2020 to 2040.

Results

In 2019, there were an estimated 80,040 (95% uncertainty interval 57,534 to 103,608) YLD and 139,132 (107,632 to 161,172) YLL caused by MS among older adults globally. The age-standardized YLD and YLL rates decreased by an average of -0.21% (95% CI -0.26 to -0.16) and - 0.2% (95% CI -0.26 to -0.14) per year for overall MS from 1990 to 2019, respectively. The number of YLL globally in 2019 was 7,891 (5,003 to 10,991) and 15,667 (10,833 to 20,076) due to smoking-attributable MS. The age-standardized YLD and YLL rates decreased by an annual average of -1.14% (95% CI -1.25 to -1.04) and - 1.15% (95% CI -1.27 to -1.03) for MS attributable to smoking. Although the global age-standardized rates of YLD and YLL for MS among older adults declined from 1990 to 2019, many regions showed increases. The largest increase in age-standardized YLD rate of MS was observed in East Asia (average annual change 1.62% [95% CI: 1.56 to 1.68]), while the largest increase in the age-standardized YLL rate occurred in High-income North America (1.74% [1.53 to 1.96]). Nationally, the age-standardized YLD and YLL rates for overall and smoking-attributable MS increased exponentially with increases in SDI level (all model p < 0.001). Furthermore, projections have also indicated an expected decrease in the age-standardized rates of YLD and YLL of MS in the elderly population from 2020 to 2040.

Conclusion

Tracking trends in MS burden among older adults provides insights into the potential shifts in disease patterns over time. The findings lay the groundwork for informed decision-making in public health and healthcare delivery, aiming to ensure that older adults with MS receive appropriate care and support.

The Role of Intestinal Microbiota and Probiotics Supplementation in Multiple Sclerosis Management

Multiple sclerosis (MS) is a neurological autoimmune disorder predominantly afflicting young adults. The etiology of MS is intricate, involving a variety of environmental and genetic factors. Current research increasingly focuses on the substantial contribution of gut microbiota in MS pathogenesis. The commensal microbiota resident within the intestinal milieu assumes a central role within the intricate network recognized as the gut-brain axis (GBA), wielding beneficial impact in neurological and psychological facets. As a result, the modulation of gut microbiota is considered a pivotal aspect in the management of neural disorders, including MS. Recent investigations have unveiled the possibility of using probiotic supplements as a promising strategy for exerting a positive impact on the course of MS. This therapeutic approach operates through several mechanisms, including the reinforcement of gut epithelial integrity, augmentation of the host's resistance against pathogenic microorganisms, and facilitation of mucosal immunomodulatory processes. The present study comprehensively explains the gut microbiome's profound influence on the central nervous system (CNS). It underscores the pivotal role played by probiotics in forming the immune system and modulating neurotransmitter function. Furthermore, the investigation elucidates various instances of probiotic utilization in MS patients, shedding light on the potential therapeutic advantages afforded by this intervention.

Prevalence and disease disability in immigrants with multiple sclerosis in Malmö, southern Sweden

BACKGROUND

Multiple sclerosis (MS) is the most common chronic demyelinating disease of the central nervous system and the major non-traumatic cause of permanent disability in young adults. Several migration studies have been performed over the years suggesting a pattern of higher disease disability in certain ethnic groups. To our knowledge, differences in disease progression in immigrants have not been studied in Sweden before. Thus, the aims of our study were to estimate the prevalence of multiple sclerosis among first-generation immigrants in the City of Malmö and to compare differences in disease severity with the native population.

METHODS

All persons with multiple sclerosis living in Malmö on prevalence day 31 Dec 2010 were included. Cases were classified according to the country of birth into Scandinavians, Western and non-Western.

RESULTS

The crude prevalence was 100/100,000 (95% CI, 80-124) among first-generation immigrants, 154/100,000 (95% CI, 137-173) among individuals with Scandinavian background, 123/100,000 (95% CI, 94-162) in the Western group and 76/100,000 (95% CI, 53-108) in the non-Western group. The mean Multiple Sclerosis Severity Score (MSSS) value among Scandinavians was 4.2 (SD 3.5), whereas the figures in the immigrant group were 4.6 (SD 3.3) and 5.2 (SD 3.7) among Westerns respectively non-Westerns, which differences were not statistically significant. When adjusting for gender, age at onset and initial disease course, the mean MSSS difference between the non-Western and the Scandinavian individuals was 1.7 (95% CI 0.18-3.3, p = 0.030). There were no differences on time to diagnosis or the time from diagnosis to treatment initiation between the three groups.

CONCLUSIONS

We found a lower prevalence among Western and non-Western first-generation immigrants compared to the Scandinavian population and a more severe disease in non-Western immigrants than in Scandinavians.

Proportion of Life Spent in Canada and the Incidence of Multiple Sclerosis in Permanent Immigrants

BACKGROUND AND OBJECTIVES

While immigrants to high-income countries have a lower risk of multiple sclerosis (MS) compared with host populations, it is unknown whether this lower risk among immigrants increases over time. Our objective was to evaluate the association between proportion of life spent in Canada and the hazard of incident MS in Canadian immigrants.

METHODS

We conducted a population-based retrospective cohort study in Ontario, using linked health administrative databases. We followed immigrants, who arrived in Ontario between 1985 and 2003, from January 1, 2003, to December 31, 2016, to record incident MS using a validated algorithm based on hospital admission or outpatient visits. We derived proportion of life spent in Canada based on age at arrival and time since immigration obtained from linked immigration records. We used multivariable proportional hazard models, adjusting for demographics and comorbidities, to evaluate the association between proportion of life in Canada and the incidence of MS, where proportion of life was modelled using restricted cubic spline terms. We further evaluated the role of age at migration (15 or younger vs older than 15 years), sex, and immigration class in sensitivity analyses.

RESULTS

We included 1.5 million immigrants (49.9% female, mean age 35.9 [SD 14.2] years) who had spent a median of 20% (Q1-Q3 10%-30%) of their life in Canada. During a mean follow-up of 13.9 years (SD 1.0), 934 (0.44/100,000 person-years) were diagnosed with MS. Compared with the median, a higher risk of MS was observed at higher values of proportion of life spent (e.g., hazard ratio [70% vs 20% proportion of life] 1.38; 1.07-1.78). This association did not vary by sex (p(sex × proportion of life) = 0.70) or immigration class (p(immigration class × proportion of life) = 0.13). The results did not vary by age at migration but were statistically significant only at higher values of proportion of life for immigrants aged 15 years or younger at arrival.

DISCUSSION

The risk of incident MS in immigrants varied with the proportion of life spent in Canada, suggesting an acculturation effect on MS risk. Further work is required to understand environmental and sociocultural factors driving the observed association.

Multiple sclerosis disease-modifying drug use by immigrants: a real-world study

Little is known about disease-modifying drug (DMD) initiation by immigrants with multiple sclerosis (MS) in countries with universal health coverage. We assessed the association between immigration status and DMD use within 5-years after the first MS-related healthcare encounter. Using health administrative data, we identified MS cases in British Columbia (BC), Canada. The index date was the first MS-related healthcare encounter (MS/demyelinating disease-related diagnosis or DMD prescription filled), and ranged from 01/January/1996 to 31/December/2012. Those included were ≥ 18 years old, BC residents for ≥ 1-year pre- and ≥ 5-years post-index date. Persons becoming permanent residents 1985-2012 were defined as immigrants, all others were long-term residents. The association between immigration status and any DMD prescription filled within 5-years post-index date (with the latest study end date being 31/December/2017) was assessed using logistic regression, reported as adjusted odds ratios (aORs) with 95% confidence intervals (CIs). We identified 8762 MS cases (522 were immigrants). Among immigrants of lower SES, odds of filling any DMD prescription were reduced, whereas they did not differ between immigrants and long-term residents across SES quintiles (aOR 0.96; 95%CI 0.78-1.19). Overall use (odds) of a first DMD within 5 years after the first MS-related encounter was associated with immigration status.

Exposure to systemic antibiotics in outpatient care and the risk of multiple sclerosis

BACKGROUND

Infections, early life exposures and the microbiome have been associated with the aetiology of multiple sclerosis (MS). Data on any possible roles of antibiotics is scarce and conflicting.

OBJECTIVE

The objective of this study was to investigate associations between outpatient systemic antibiotic exposure and the risk of MS in a nationwide case-control setting.

METHODS

Patients with MS were identified from the nation MS registry and their exposure to antibiotics was compared with that of persons without MS, provided by the national census authority. Antibiotic exposure was investigated using the national prescription database and analyzed by Anatomical Therapeutic Chemical (ATC) category.

RESULTS

Among the 1830 patients with MS and 12765 control persons, there were no associations between exposure to antibiotics in childhood (5-9 years) or adolescence (10-19 years) and the subsequent risk of MS. There was also no association between antibiotic exposure 1-6 years before disease onset and the risk of MS, save for exposure to fluoroquinolones in women (odds ratio: 1.28; 95% confidence interval: 1.03, 1.60; p = 0.028) which is probably associated with the increased infection burden in the MS prodrome.

CONCLUSION

Use of systemic prescription antibiotics was not associated with subsequent MS risk.

Differential impact of environmental factors on systemic and localized autoimmunity

The influence of environmental factors on the development of autoimmune disease is being broadly investigated to better understand the multifactorial nature of autoimmune pathogenesis and to identify potential areas of intervention. Areas of particular interest include the influence of lifestyle, nutrition, and vitamin deficiencies on autoimmunity and chronic inflammation. In this review, we discuss how particular lifestyles and dietary patterns may contribute to or modulate autoimmunity. We explored this concept through a spectrum of several autoimmune diseases including Multiple Sclerosis (MS), Systemic Lupus Erythematosus (SLE) and Alopecia Areata (AA) affecting the central nervous system, whole body, and the hair follicles, respectively. A clear commonality between the autoimmune conditions of interest here is low Vitamin D, a well-researched hormone in the context of autoimmunity with pleiotropic immunomodulatory and anti-inflammatory effects. While low levels are often correlated with disease activity and progression in MS and AA, the relationship is less clear in SLE. Despite strong associations with autoimmunity, we lack conclusive evidence which elucidates its role in contributing to pathogenesis or simply as a result of chronic inflammation. In a similar vein, other vitamins impacting the development and course of these diseases are explored in this review, and overall diet and lifestyle. Recent work exploring the effects of dietary interventions on MS showed that a balanced diet was linked to improvement in clinical parameters, comorbid conditions, and overall quality of life for patients. In patients with MS, SLE and AA, certain diets and supplements are linked to lower incidence and improved symptoms. Conversely, obesity during adolescence was linked with higher incidence of MS while in SLE it was associated with organ damage. Autoimmunity is thought to emerge from the complex interplay between environmental factors and genetic background. Although the scope of this review focuses on environmental factors, it is imperative to elaborate the interaction between genetic susceptibility and environment due to the multifactorial origin of these disease. Here, we offer a comprehensive review about the influence of recent environmental and lifestyle factors on these autoimmune diseases and potential translation into therapeutic interventions.

A national case-control study investigating demographic and environmental factors associated with NMOSD

BACKGROUND

Risk factors for aquaporin-4 (AQP4+) antibody neuromyelitis optica spectrum disorder (NMOSD) are not well-established.

OBJECTIVE

To investigate demographic and environmental factors associated with NMOSD using a validated questionnaire and case-control design.

METHODS

We enrolled patients with AQP4 + NMOSD through six Canadian Multiple Sclerosis Clinics. Participants completed the validated Environmental Risk Factors in Multiple Sclerosis Study (EnvIMS) questionnaire. Their responses were compared to those of 956 unaffected controls from the Canadian arm of EnvIMS. We calculated odds ratios (ORs) for the association between each variable and NMOSD using logistic regression and Firth's procedure for rare events.

RESULTS

In 122 participants (87.7% female) with NMOSD, odds of NMOSD in East Asian and Black participants were ⩾8 times that observed in White participants. Birthplace outside Canada was associated with an increased risk of NMOSD (OR = 5.5, 95% confidence interval (CI) = 3.6-8.3) as were concomitant autoimmune diseases (OR = 2.7, 95% CI = 1.4-5.0). No association was observed with reproductive history or age at menarche.

CONCLUSION

In this case-control study, risk of NMOSD in East Asian and Black versus White individuals was greater than that observed in many previous studies. Despite the preponderance of affected women, we did not observe any association with hormonal factors such as reproductive history or age at menarche.

Role of environmental factors in multiple sclerosis

INTRODUCTION

Environmental factors play a significant role in the pathogenesis and progression of multiple sclerosis (MS), either acting alone or by interacting with other environmental or genetic factors. This cumulative exposure to external risk factors is highly complex and highly variable between individuals.

AREAS COVERED

We narratively review the current evidence on the role of environment-specific risk factors in MS onset and progression, as well as the effect of gene-environment interactions and the timing of exposure We have reviewed the latest literature, by Ovid Medline, retrieving the most recently published systematic reviews and/or meta-analyses and more recent studies not previously included in meta-analyses or systematic reviews.

EXPERT OPINION

There is some good evidence supporting the impact of some environmental risk factors in increasing the risk of developing MS. Tobacco smoking, low vitamin D levels and/or low sun exposure, Epstein Barr Virus (EBV) seropositivity and a history of infectious mononucleosis may increase the risk of developing MS. Additionally, there is some evidence that gene-smoking, gene-EBV, and smoking-EBV interactions additively affect the risk of MS onset. However, the evidence for a role of other environmental factors in MS progression is limited. Finally, there is some evidence that tobacco smoking, insufficient vitamin D levels and/or sun exposure have impacts on MS phenotypes and various markers of disease activity including relapse, disability progression and MRI findings. Clearly the effect of environmental factors on MS disease course is an area that requires significantly more research.

High prevalence of comorbidities at diagnosis in immigrants with multiple sclerosis

Background:

Multiple sclerosis (MS) has been associated with certain comorbidities in general population studies, but it is unknown how comorbidity may affect immigrants with MS.

Objective:

To compare prevalence of comorbidities in immigrants and long-term residents at MS diagnosis, and in matched control populations without MS.

Methods:

We identified incident MS cases using a validated definition applied to health administrative data in Ontario, Canada, from 1994 to 2017, and categorized them as immigrants or long-term residents. Immigrants and long-term residents without MS (controls) were matched to MS cases 3:1 on sex, age, and geography.

Results:

There were 1534 immigrants and 23,731 long-term residents with MS matched with 4585 and 71,193 controls, respectively. Chronic obstructive pulmonary disease (COPD), diabetes, hypertension, ischemic heart disease, migraine, epilepsy, mood/anxiety disorders, schizophrenia, inflammatory bowel disease (IBD), and rheumatoid arthritis were significantly more prevalent among immigrants with MS compared to their controls. Prevalence of these conditions was generally similar comparing immigrants to long-term residents with MS, although COPD, epilepsy, IBD, and mood/anxiety disorders were less prevalent in immigrants.

Conclusion:

Immigrants have a high prevalence of multiple comorbidities at MS diagnosis despite the “healthy immigrant effect.” Clinicians should pay close attention to identification and management of comorbidity in immigrants with MS.

Joinpoint Regression Analysis of Trends in Multiple Sclerosis Incidence in Kuwait: 1980-2019

BACKGROUND

Multiple sclerosis (MS) is a chronic inflammatory demyelinating and neurodegenerative disease of the central nervous system with unknown precise etiology. Temporally, a tendency for increasing MS incidence has been recorded worldwide. This cross-sectional cohort study sought to quantify trends in the age-standardized incidence rates (ASIRs) (per million person-years) of MS in Kuwait from 1980 to 2019, overall and by subcohorts defined by age at MS onset, sex, and nationality.

METHODS

MS incidence data from 1980 to 2019 were obtained from the Kuwait National MS Registry (KNMSR). Using midyear relevant Kuwait population as denominator and the World Standard Population as a reference, MS ASIRs overall and by subcohorts defined by age at onset (0-19, 20-39, and 40+ years), sex (male and female), and nationality (Kuwaiti and non-Kuwaiti) were computed. Joinpoint regression analysis was conducted to estimate average annual percent change (AAPC) and its 95% confidence interval (CI) overall and by subcohorts.

RESULTS

During 1980-2019, a total of 1,764 MS incident cases of 95.6 million person-years at-risk were diagnosed and registered in KNMSR. The overall MS ASIR (per million person-years) during the study period was 34.1 (95% CI: 16.1, 52.1). Between 1980 and 2010, in the total cohort, ASIRs of MS significantly increased by 13% (AAPC = 13.0; 95% CI: 10.8, 15.3; p < 0.001), followed by statistically nonsignificant declining trend during the ensuing period (AAPC = -3.8; 95% CI: -14.8, 8.8; p = 0.522). Joinpoint regression analysis revealed that 2 subcohorts of Kuwaiti females each with one joinpoint had significant increasing trends in MS ASIRs (0- to 19-year-old Kuwaiti females, AAPC: 1980-2009, 81.0; 95% CI: 58.2, 107.0; p = 0.001; 20- to 39-year-old Kuwaiti females, AAPC: 1980-1999, 131.7; 95% CI: 26.9, 322.8; p = 0.021). Additionally, of remaining 10, 6 subcohorts had significantly (p < 0.05) increasing trends in MS ASIRs from 1980 to 2019.

CONCLUSIONS

From 1980 to 2010, Kuwait has an overall significantly increasing trend in MS ASIRs followed by a nonsignificant declining drift in the ensuing period. The increasing trend in MS risk appeared to be driven by increased risk among Kuwaiti females younger than 40 years. The underlying factors modulating MS risk in Kuwait need further studies.

Multiple sclerosis among first- and second-generation immigrant groups in Sweden

OBJECTIVES

Risk of multiple sclerosis (MS) is low among first-generation immigrants in Sweden. We aimed to study incident MS in first- and second-generation immigrant groups.

MATERIALS & METHODS

We included adults aged 18 years and older in Sweden in first-generation (n = 6 042 891) and second-generation (n = 4 860 469) sub-studies. MS was defined via two diagnoses in the Swedish National Patient Register. MS risk was estimated by Cox regression, with hazard ratios (HRs) and 95% confidence intervals (CI), in different immigrant groups, using Swedish-born as referents in first-generation sub-study, and individuals with Swedish-born parents in the second-generation. Full models were adjusted for age, geographic residence in Sweden, educational level, marital status, neighborhood socioeconomic status, and co-morbidity.

RESULTS

MS was diagnosed among 10 746 individuals in the first-generation sub-study, (men 3055 and women 7691), and 11 737 in the second-generation sub-study (men 3549 and women 8188) in the period 1998-2015. The annual incidence rate was higher in Swedish-born compared to foreign-born, 11.5 vs 6.3 per 100 000 person-years (age-standardized to the European standard population). Fully adjusted HRs were lower in first-generation immigrant men (HR 0.72, 0.64-0.82) and women (HR 0.67, 0.62-0.73), and in second-generation immigrant men (HR 0.88, 0.79-0.97) and women (HR 0.79; 0.73-0.84). Among first-generation immigrants, lower HRs were found in most groups.

SIGNIFICANCE

The MS risk was lower in first- and second-generation immigrants compared to Swedish-born or individuals with Swedish-born parents.

Clinical and MRI characteristics of multiple sclerosis in patients of Middle Eastern and North African ancestry residing in Ontario, Canada

BACKGROUND

Multiple sclerosis (MS) incidence is rising in traditionally low-burden regions, including the Middle East and North Africa (MENA).

OBJECTIVES

Our objective was to evaluate disease characteristics in MS patients of MENA descent (MENA-MS).

METHODS

MENA-MS patients and age- and sex-matched MS patients of European descent (EUR-MS) were identified through the MS Clinic Registry of St. Michael's Hospital in Toronto, Canada. Disease activity and severity were evaluated by the annualized relapse rate (ARR), magnetic resonance imaging (MRI) activity, change in the Expanded Disability Status Scale (EDSS), progression index (PI), and MS Severity Score (MSSS).

RESULTS

All MS patients within the registry identified to be of MENA origin (n = 192), and age- and sex-matched EUR-MS patients were included. Mean age was 42.9 years, 67% female. A total of 25% and 24% of EUR-MS and MENA-MS had progressive disease, with similar mean disease durations (11.5 and 11.4 years, respectively). Clinical and radiological disease activity (ARR, proportion with new/enlarging MRI lesions) was similar. MENA-MS showed greater disability progression over time (EDSS change = 0.24 vs. 0.06, p = 0.01), a higher MSSS (3.12 vs. 2.67, p = 0.04), and higher PI (0.34 vs. 0.27, p = 0.07).

CONCLUSION

MENA-MS patients demonstrate higher disease severity compared to EUR-MS patients, despite having similar inflammatory measures of disease activity, with disability progression in the absence of relapses. These observations illustrate the importance of the intersections of environmental, socioeconomic, and genetic determinants in optimizing individualized MS care.

Low sun exposure increases multiple sclerosis risk both directly and indirectly

Objective

We aimed to study (1) to what extent the influence of low sun exposure on multiple sclerosis (MS) risk is mediated by low vitamin D levels; (2) whether low sun exposure or vitamin D deficiency act synergistically with HLA-DRB1*15:01 and absence of HLA-A*02:01.

Methods

We used two population-based case–control studies (7069 cases, 6632 matched controls). Subjects with different HLA alleles, sun exposure habits and vitamin D status were compared regarding MS risk, by calculating odds ratios (OR) with 95% confidence intervals (CI) employing logistic regression. Mediation analysis was used to identify the potential mediation effect of vitamin D on the relationship between low sun exposure and MS risk.

Results

Low sun exposure increased MS risk directly as well as indirectly, by affecting vitamin D status. The direct effect, expressed as OR, was 1.26 (95% CI 1.04–1.45) and the indirect effect, mediated by vitamin D deficiency, was 1.10 (95% CI 1.02–1.23). Of the total effect, nearly 30% was mediated by vitamin D deficiency. There was a significant interaction between low sun exposure and vitamin D deficiency (attributable proportion due to interaction 0.3, 95% CI 0.04–0.5) accounting for about 12% of the total effect. Further, both factors interacted with HLA-DRB1*15:01 to increase MS risk.

Interpretation

Our findings indicate that low sun exposure acts both directly on MS risk as well as indirectly, by leading to low vitamin D levels. The protective effect of sun exposure thus seems to involve both vitamin D and non-vitamin D pathways, which is of relevance for prevention, in particular for those with a genetic susceptibility to MS.

Electronic supplementary material

The online version of this article (10.1007/s00415-019-09677-3) contains supplementary material, which is available to authorized users.