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Background: Environmental factors are associated with acquiring multiple sclerosis (MS) particularly in adolescence. Objective: To test for association between MS and exposure to passive smoking at the age of 10–19. Methods: A total of 919 patients from the Danish MS Registry and Biobank and 3419 healthy blood donors who had not smoked before the age of 19 were targeted. We analyzed separately for each sex and for those never-smokers (cohort 1) and active smokers above the age of 19 (cohort 2). All participants completed standardized questionnaires about smoking and lifestyle. We matched cases and controls in the ratio of 1:2 by propensity scores discarding unmatchable individuals and used logistic regression adjusted for all covariates and interactions. Results: After matching, we included 110/213 male cases/controls and 232/377 female case/controls in cohort 1. In cohort 2, the numbers were 160/320 and 417/760, respectively. Among women in cohort 1, the odds ratio (OR) for MS by passive smoking at the age of 10–19 was 1.432 ( p = 0.037) but in men it was 1.232 ( p = 0.39). Among men in cohort 2, OR was 1.593 ( p = 0.022) but among women it was only 1.102 ( p = 0.44). Conclusion: Among never smokers, female MS cases were more often than female controls reported with passive smoking between the age of 10 and 19, and among smokers above the age of 19, male MS patients were more often than male controls reported with passive smoking.

Background: Current knowledge concerning the association between exposure to stressful life-events (SFLEs) in childhood and later risk of multiple sclerosis (MS) is sparse. Objectives: We studied the associations between SFLEs in childhood and subsequent risk of MS in a nationwide cohort of 2.9 million Danes born from 1968 to 2011. Methods: A SFLE in childhood was defined as exposure before age 18 years to parental divorce, parental death, or death of a sibling, using information from the Danish Civil Registration System. MS cases in the cohort were identified in the Danish Multiple Sclerosis Registry. Associations of SFLE with MS risk were evaluated by incidence rate ratios (RR) of MS obtained in log-linear Poisson regression models. Results: Persons exposed to any SFLE in childhood were at 11% elevated risk of MS (RR = 1.11; 95% confidence interval: 1.03–1.20), compared to non-exposed persons. Stratification by subtype of SFLE showed that parental death and death of a sibling were not associated with MS risk. However, persons exposed to parental divorce were at 13% increased risk of developing MS compared to non-exposed (RR = 1.13; 1.04–1.23). Conclusions: Associations of SFLEs in childhood with risk of MS are weak. However, parental divorce is somehow associated with modestly increased risk of MS.

Background: The female preponderance in incidence of multiple sclerosis (MS) calls for investigations into sex differences in comorbidity with other autoimmune diseases (ADs). Objectives: To determine whether male and female patients with MS have a higher frequency of autoimmune comorbidity than controls, and to describe the type and frequency of ADs that are associated with MS. Methods: Our database was established by linkage of the Danish MS Registry to The Danish National Patient Register and consisted of 1403 patients of both sexes with clinical onset of MS between 2000 and 2004, and 25 matched controls for every case. Results: None of the ADs occurred more frequently in female cases than in controls. Male cases were more likely to have Type I diabetes mellitus (odds ratio (OR) = 3.34; 95% CI 1.40 – 7.02; p < 0.008), Crohn’s disease (OR = 5.03; 95% CI 1.18 – 16.10; p = 0.03) and systemic lupus erythematosus (OR = 12.55; 95% CI 1.62 – 69.95; p = 0.02) than male controls. Conclusions: Autoimmune disorders are rare, but some of them tend to occur together with MS at a higher rate than in controls. Although women are generally more prone to ADs than men, significantly increased occurrence of other ADs were only found in male MS patients.

Background: Apart from a recent study reporting a 2- to 3-fold increased risk of multiple sclerosis (MS) among women and men who were delivered by Cesarean section (C-section), little attention has been given to the possible association between mode of delivery and the risk of MS. Objectives: We studied the association between C-section and risk of MS, in a cohort of 1.7 million Danes born from 1973 to 2005. Methods: Information on C-section and MS was obtained from the Danish Medical Birth Register and the Danish MS Register, respectively. The association between C-section and MS was evaluated by means of MS incidence rate ratios (RR) with 95% confidence intervals (CI) obtained in log-linear Poisson regression analyses. Results: There were 930 cases of MS in the study cohort, of whom 80 (9%) were delivered by C-section. Overall, we found there was no significant association between C-section and risk of MS (RR = 1.17; 0.92–1.46). Analyses stratified by sex revealed no unusual risk of MS for women (RR = 1.08: 0.80–1.42) nor men (RR = 1.37: 0.91–1.98). A supplementary sibling-matched Cox regression analysis likewise suggested there was no excess risk of MS in persons delivered by C-section (HR = 1.03; 0.63–1.69). Conclusions: Mode of delivery appears to be unimportant in relation to MS development in the offspring.

Background: Patients with multiple sclerosis (MS) are potentially at high risk of fracture due to falls and osteoporosis. Objective: To estimate incidence rates of fractures in MS patients, stratified by fracture type, sex and age, and to compare these rates with controls. Methods: The case population consisted of all patients with an accepted diagnosis of MS in the Danish MS Registry (1949–2007). Data were linked to the National Hospital Discharge Register (1977–2007). Patients with MS ( n = 11,157) were 1:6 matched by year of birth, gender, calendar time and region to persons without MS (controls). Incidence rates of fracture were estimated as the number of fractures per 1000 person-years. Incidence rate ratios (IRRs) were calculated by dividing fracture rates in MS patients by fracture rates in controls. Results: Among patients with MS, the incidence rate of any fracture yielded 22.8 per 1000 person-years. The IRR of any fracture between MS patients and controls was 1.40 (95% CI 1.33–1.46). In particular, IRRs of tibia fracture (3.36 [2.75–4.11]), femur fracture (6.66 [5.06–8.76]) and hip fracture (3.20 [2.83–3.62]) were elevated in MS patients versus controls. Conclusion: Fractures occurred more often in patients with MS, especially fractures of the tibia, hip and femur.

Background: In the clinical trials about 9% of natalizumab treated multiple sclerosis (MS) patients generated anti-natalizumab antibodies, of which 6% were persistent and 3% transient. The occurrence of antibodies reduced serum levels of natalizumab, decreased bio-efficacy, and abrogated the therapeutic efficacy. Objective: The objective was to assess the frequency of anti-natalizumab antibodies in an unselected cohort of patients from four different countries. Methods: We measured anti-natalizumab antibodies in a large cohort of 4881 unselected patients from four MS centres that systematically measured antibodies in patients treated with natalizumab. We applied the same ELISA assay developed by Biogen Idec and used in the pivotal trials of natalizumab. Results: Antibodies occurred in 4.5% (95% confidence interval, CI: 4.0–5.1%) of the patients, and were persistent in 3.5% (95% CI: 3.0–4.0%) and transient in 1.0% (95% CI: 0.7–1.3%) of the patients. The frequencies of permanently antibody positive patients did not show statistically significant differences between the four centres, whereas the frequencies of transiently antibody positive patients showed some variations. Conclusion: The frequencies of antibodies appeared to be of the same magnitude in the four centres, but might be less than in the pivotal studies of natalizumab.

Multiple sclerosis is an inflammatory disease of the central nervous system of unknown aetiology. Its prevalence varies by ethnicity and place: persons of northern European descent are at increased risk while persons living at lower latitudes appear to be protected against the disease. The Danish Multiple Sclerosis Registry is a national registry established in 1956 after a population-based survey which receives information from numerous sources. It is considered to be more than 90% complete, with a validity of 94%. Using data from the Registry, we calculated prevalences per 100,000 inhabitants. The standardized prevalence of multiple sclerosis increased from 58.8 (95% confidence interval: 54.9—62.7) in 1950 to 154.5 per 100,000 (95% confidence interval: 148.8—160.2) in 2005, and the female to male ratio increased from 1.31 in 1950 to 2.02 in 2005. The increase in prevalence is due to both increased survival of multiple sclerosis patients and an increased incidence rate. The rise in prevalence in the past 50 years is probably due more to environmental factors than to genetic changes in the Danish population. Among women, environmental changes could include older age at first birth, use of oral contraceptives, or changes in sun behaviour and/or vitamin D status.

Biomarkers that allow the identification of patients with multiple sclerosis (MS) with an insufficient response to immunomodulatory treatment would be desirable, as currently available treatments are only incompletely efficacious. Previous studies have shown that the expression of CD25, CD26 and CCR5 on T cells is altered in patients with active MS. We studied the expression of these molecules by flow cytometry in patients followed for six months during immunomodulatory treatment. In interferon (IFN)-β-treated patients, we found that the hazard ratio for developing an attack was 2.8 in patients with CD26+CD4+T cell counts above median, and this risk was independent of the risk conferred by neutralizing anti-IFN-β antibodies. CD26+CD4+T cell counts may identify patients with MS at increased risk of attack during treatment with IFN-β.

Background: Identification of MS registries and databases that are currently in use in Europe as well as a detailed knowledge of their content and structure is important in order to facilitate comprehensive analysis and comparison of data. Methods: National MS registries or databases were identified by literature search, from the results of the MS Barometer 2011 and by asking 33 national MS societies. A standardized questionnaire was developed and sent to the registries’ leaders, followed by telephone interviews with them. Results: Twenty registries were identified, with 13 completing the questionnaire and seven being interviewed by telephone. These registries differed widely for objectives, structure, collected data, and for patients and centres included. Despite this heterogeneity, common objectives of the registries were epidemiology ( n=10), long-term therapy outcome ( n=8), healthcare research ( n=9) and support/basis for clinical trials ( n=8). While physician-based outcome measures (EDSS) are used in all registries, data from patients’ perspectives were only collected in six registries. Conclusions: The detailed information on a large number of national MS registries in Europe is a prerequisite to facilitating harmonized integration of existing data from MS registries and databases, as well as comprehensive analyses and comparison across European populations.

After approval by the European Union in 1996 of interferon-beta for treatment of relapsing-remitting multiple sclerosis (RRMS), 862 patients in Denmark have received treatment (by April 1999), and 304 of those were enrolled into an open labelled randomised trial to compare the efficacy and tolerability of treatment with interferon-beta-1b (Betaferon) 8 MIU subcutaneous every other day and interferon-beta-1a (Rebif) 6 MIU subcutaneous once a week. Primary and secondary end-points included: (1) the relapse rate, (2) tolerability, (3) neutralizing antibody formation using the same specialised laboratory and validated assay, (4) time to first relapse, (5) time to sustained progression, and (6) number of gadolinium-enhancing lesions in T1-weighted MRI and the total lesion load in T2-weighted MRI. All the records are kept in a nationwide clinical database connected with the Danish Multiple Sclerosis Registry. The randomised trial will be completed by the end of 1999, and the results are not yet available. The annual relapse rate in all treated patients until April 1999 was 0.73, the annual rate of steroid treated relapses was 0.21. By 1 April 1999 8.8% of the patients had discontinued treatment and 10.4% had changed to another interferon-beta preparation. It has been planned to extend the follow-up of all patients treated according to the Danish National Protocol for a period of several years. The continuous and nation-wide registration of the course of the disease in interferon-beta treated RRMS patients may provide valuable knowledge of the treatment-modified long-term course of the disease in a cohort of patients, selected on the basis of well-defined criteria.

The incidence of multiple sclerosis (MS) in nurses during the period 1980-1996 was calculated in a nationwide study. The cohort consisted of 69 428 nurses, 2185 men and 67243 women. Sixty (two men and 58 women) with definite MS were observed, whereas 69.3 were expected. We found no significant difference between the observed and expected number of MS cases (standardized incidence ratio =0.87; 95% confidence interval, 0.66-1.12).