Association Between Alcohol Consumption and Disability Accumulation in Multiple Sclerosis.

BACKGROUND AND OBJECTIVES: Previous studies have indicated that alcohol consumption is associated with multiple sclerosis (MS) disease progression. We aimed to study the influence of alcohol consumption habits on disease progression and health-related quality of life in MS. METHODS: We categorized patients from 2 population-based case-control studies by alcohol consumption habits at diagnosis and followed them up to 15 years after diagnosis through the Swedish MS registry regarding changes in the Expanded Disability Status Scale (EDSS) and Multiple Sclerosis Impact Scale 29 (MSIS-29). We used Cox regression models with 95% confidence intervals (CIs) using 24-week confirmed disability worsening, EDSS 3, EDSS 4, and physical and psychological worsening from the patient's perspective as end points. RESULTS: Our study comprised 9,051 patients with MS, with a mean age of 37.5 years at baseline/diagnosis. Compared with nondrinking, low and moderate alcohol consumption was associated with reduced risk of EDSS-related unfavorable outcomes (hazard ratios between 0.81 and 0.90) and with reduced risk of physical worsening. The inverse association was confined to relapsing-remitting MS and was more pronounced among women. High alcohol consumption did not significantly affect disease progression. The inverse relationship between low-moderate alcohol consumption and disability progression became stronger when we only included those who had not changed their alcohol consumption during follow-up (hazard ratios between 0.63 and 0.71). There were no differences in measures of disability at baseline between drinkers who continued drinking alcohol after diagnosis and those who later discontinued. Our findings speak against bias due to reverse causation. DISCUSSION: Low and moderate alcohol consumption was associated with more favorable outcomes in relapsing-remitting MS, compared with nondrinking, while there was no significant influence of high alcohol consumption on disease outcomes.

Adolescent sleep patterns, genetic predisposition, and risk of multiple sclerosis.

STUDY OBJECTIVES: Shift work, insufficient sleep, and poor sleep quality at young age have been associated with increased risk of multiple sclerosis (MS). This study aimed to investigate the potential interaction between aspects of inadequate sleep (short sleep, phase shift, and poor sleep quality) during adolescence and HLA-DRB1*15:01 in relation to MS risk. METHODS: We used a Swedish population-based case-control study (1253 cases and 1766 controls). Participants with different sleep patterns during adolescence and HLA-DRB1*15:01 status were compared regarding MS risk by calculating odds ratios with 95% confidence intervals (CI) using logistic regression models. Additive interaction between aspects of inadequate sleep and HLA-DRB1*15:01 status was assessed by calculating the attributable proportion due to interaction (AP) with 95% CI. RESULTS: Short sleep duration (<7 hours/night) during adolescence acted synergistically with HLA-DRB1*15:01, increasing the risk of MS (AP 0.38, 95% CI: 0.01 to 0.75, p = .04). Similarly, subjective low sleep quality during adolescence interacted with HLA-DRB1*15:01 regarding risk of MS (AP 0.30, 95% CI: 0.06 to 0.56, p = .03), whereas phase shift did not significantly influence the risk of the disease, irrespective of HLA-DRB1*15:01 status. CONCLUSIONS: Our findings underscore the importance of addressing inadequate sleep during adolescence, particularly in the context of the HLA-DRB1*15:01 allele, as it appears to amplify the risk of subsequently developing MS.

Genetics of immune response to Epstein-Barr virus: prospects for multiple sclerosis pathogenesis.

Epstein-Barr virus (EBV) infection has been advocated as a prerequisite for developing multiple sclerosis (MS) and possibly the propagation of the disease. However, the precise mechanisms for such influences are still unclear. A large-scale study investigating the host genetics of EBV serology and related clinical manifestations, such as infectious mononucleosis (IM), may help us better understand the role of EBV in MS pathogenesis. This study evaluates the host genetic factors that influence serological response against EBV and history of IM and cross-evaluates them with MS risk and genetic susceptibility in the Swedish population. Plasma IgG antibody levels against EBV nuclear antigen-1 [EBNA-1, truncated = amino acids (aa) (325-641), peptide = aa(385-420)] and viral capsid antigen p18 (VCAp18) were measured using bead-based multiplex serology for 8744 MS cases and 7229 population-matched control subjects. The MS risk association for high/low EBV antibody levels and history of IM was compared to relevant clinical measures along with sex, age at sampling, and associated HLA allele variants. Genome-wide and HLA allele association analyses were also performed to identify genetic risk factors for EBV antibody response and IM history. Higher antibody levels against VCAp18 [odds ratio (OR) = 1.74, 95% confidence interval (CI) = 1.60-1.88] and EBNA-1, particularly the peptide (OR = 3.13, 95% CI = 2.93-3.35), were associated with an increased risk for MS. The risk increased with higher anti-EBNA-1 IgG levels up to 12× the reference risk. We also identified several independent HLA haplotypes associated with EBV serology overlapping with known MS risk alleles (e.g. DRB1*15:01). Although there were several candidates, no variants outside the HLA region reached genome-wide significance. Cumulative HLA risk for anti-EBNA-1 IgG levels, particularly the peptide fragment, was strongly associated with MS. In contrast, the genetic risk for high anti-VCAp18 IgG levels was not as strongly associated with MS risk. IM history was not associated with class II HLA genes but negatively associated with A*02:01, which is protective against MS. Our findings emphasize that the risk association between anti-EBNA-1 IgG levels and MS may be partly due to overlapping HLA associations. Additionally, the increasing MS risk with increasing anti-EBNA-1 levels would be consistent with a pathogenic role of the EBNA-1 immune response, perhaps through molecular mimicry. Given that high anti-EBNA-1 antibodies may reflect a poorly controlled T-cell defence against the virus, our findings would be consistent with DRB1*15:01 being a poor class II antigen in the immune defence against EBV. Last, the difference in genetic control of IM supports the independent roles of EBNA-1 and IM in MS susceptibility.

Association between sun exposure habits and disease progression in multiple sclerosis.

BACKGROUND AND PURPOSE: Higher latitude has been associated with increased occurrence of multiple sclerosis (MS) and with more severe disease. The aim was to study the impact of sun exposure habits on MS disease progression and health-related quality of life. METHODS: Patients from a population-based case-control study were categorized based on sun exposure habits at diagnosis and were followed up to 15 years post-diagnosis through the Swedish MS registry (n = 3314) with regard to changes in Expanded Disability Status Scale (EDSS). Linear mixed models were used to analyse long-term changes, while Cox regression models, with 95% confidence intervals, were used to investigate outcomes, including 24-week confirmed diasability worsening, EDSS3, EDSS4, and physical worsening as measured by the physical component of the Multiple Sclerosis Impact Scale 29. RESULTS: Compared to average sun exposure (median value), low exposure to sunlight was associated with faster EDSS progression, increased risk of confirmed disability worsening (hazard ratio [HR] 1.48, 95% CI 1.21-1.81), increased risk of reaching EDSS 3 (HR 1.35, 95% CI 1.02-1.79), EDSS 4 (HR 1.47, 95% CI 1.01-2.20) and self-reported physical worsening (HR 1.27, 95% CI 1.00-1.62). Significant trends revealed a lower risk of unfavourable outcomes with increasing sun exposure. CONCLUSIONS: Very low levels of sun exposure are associated with worse disease progression and health-related quality of life in patients with MS.

Medically unexplained symptoms are common in women in tertiary neurological healthcare center: A survey cohort study of persons investigated for suspected multiple sclerosis.

BACKGROUND: A significant proportion of individuals with suspicious onset of multiple sclerosis (MS) does not fulfill the diagnostic criteria. Although some receive other diagnoses, many remain undiagnosed and lack healthcare follow-up. This study aimed to characterize persons with undetermined diagnosis (PwUD) through a questionnaire. METHODS: Incident cases with suspected MS were consecutively admitted to a tertiary neurological healthcare center in a prospective cohort study. Those who remained undiagnosed after 40 months (mean, range 31-52) were considered PwUD. They completed a modified questionnaire, previously used in a population-based case-control study of incident MS cases. Their responses were compared with two control cohorts, persons with MS (PwMS) and healthy controls, randomly selected from national registries, matched by age, gender, and area of residence. RESULTS: Out of 271 patients with suspected MS onset, 72 (20.3%) were PwUD with a female majority (79%). The response rate was 83% and 39% reported persisting MS-like symptoms. Compared to controls (n = 548) and PwMS (n = 277), fewer PwUD were currently smoking (p = .4 and p = .03), consumed less alcohol (p = .04 and p = .01), and had children (p = .02 and p = .002). PwUD reported occurrence of other autoimmune disease in 29%, higher compared to PwMS and controls (p < .001 and p < .001). CONCLUSIONS: UD is common among persons investigated for suspected MS, in particular among female parents. Our data suggest that PwUD can be characterized as nonsmokers with low alcohol consumption and a higher prevalence of autoimmune disease, in particular thyroid disease.

Head trauma results in manyfold increased risk of multiple sclerosis in genetically susceptible individuals.

BACKGROUND: Large register-based studies have reported an association between head trauma and increased risk of multiple sclerosis (MS). We aimed to investigate possible interactions between head trauma and MS-associated HLA genes in relation to MS risk. METHODS: We used a Swedish population-based case-control study (2807 incident cases, 5950 matched controls with HLA genotypes available for 2057 cases, 2887 controls). Subjects with and without a history of self-reported head trauma were compared regarding MS risk, by calculating ORs with 95% CIs using logistic regression models. Additive interaction between head trauma, HLA-DRB1*1501 and absence of HLA-A*0201, was assessed by calculating the attributable proportion (AP) due to interaction. RESULTS: A history of head trauma was associated with a 30% increased risk of subsequently developing MS (OR 1.34, 95% CI 1.17 to 1.53), with a trend showing increased risk of MS with increasing number of head impacts (p=0.03). We observed synergistic effects between recent head trauma and HLA-DRB1*15:01 as well as absence of HLA*02:01 in relation to MS risk (each AP 0.40, 95% CI 0.1 to 0.7). Recent head trauma in individuals with both genetic risk factors rendered an 18-fold increased risk of MS, compared with those with neither the genetic risk factors nor a history of head trauma (OR 17.7, 95% CI 7.13 to 44.1). CONCLUSIONS: Our findings align with previous observations of a dose-dependent association between head trauma and increased risk of MS and add a novel aspect of this association by revealing synergistic effects between recent head trauma and MS-associated HLA genes.

Risk factors for multiple sclerosis in the context of Epstein-Barr virus infection.

Compelling evidence indicates that Epstein Barr virus (EBV) infection is a prerequisite for multiple sclerosis (MS). The disease may arise from a complex interplay between latent EBV infection, genetic predisposition, and various environmental and lifestyle factors that negatively affect immune control of the infection. Evidence of gene-environment interactions and epigenetic modifications triggered by environmental factors in genetically susceptible individuals supports this view. This review gives a short introduction to EBV and host immunity and discusses evidence indicating EBV as a prerequisite for MS. The role of genetic and environmental risk factors, and their interactions, in MS pathogenesis is reviewed and put in the context of EBV infection. Finally, possible preventive measures are discussed based on the findings presented.

Treatment Options for Epstein-Barr Virus-Related Disorders of the Central Nervous System.

Epstein-Barr virus (EBV), a causative agent for several types of lymphomas and mucosal cancers, is a human lymphotropic herpesvirus with the capacity to establish lifelong latent infection. More than 90% of the human population worldwide is infected. The primary infection is usually asymptomatic in childhood, whereas infectious mononucleosis (IM) is common when the infection occurs in adolescence. Primary EBV infection, with or without IM, or reactivation of latent infection in immunocompromised individuals have been associated with a wide range of neurologic conditions, such as encephalitis, meningitis, acute disseminated encephalomyelitis, and cerebellitis. EBV is also involved in malignant lymphomas in the brain. An increasing number of reports on EBV-related disorders of the central nervous system (CNS) including the convincing association with multiple sclerosis (MS) have put in focus EBV-related conditions beyond its established link to malignancies. In this review, we present the clinical manifestations of EBV-related CNS-disorders, put them in the context of known EBV biology and focus on available treatment options and future therapeutic approaches.

Inverse association between Mediterranean diet and risk of multiple sclerosis.

OBJECTIVE: There is some evidence implicating diet in the development of inflammatory diseases. We aimed to study the influence of dietary habits on the risk of developing multiple sclerosis (MS). METHODS: We used a population-based case-control study recruiting incident cases of MS (1953 cases, 3557 controls). Subjects with different dietary habits 5 years prior to MS diagnosis were compared regarding MS risk by calculating odds ratios (OR) with 95% confidence intervals (CI) using logistic regression models. Adjustment was made for a large number of environmental and lifestyle habits, including ancestry, smoking, alcohol consumption, body mass index, physical activity, and sun exposure habits. RESULTS: Mediterranean diet was associated with lower risk of developing MS (adjusted OR = 0.54, 95% CI: 0.34-0.86, p = 0.009), compared with Western-style diet. There was no significant association between vegetarian/vegan diet and MS risk (adjusted OR = 0.96, 95% CI: 0.75-1.24, p = 0.976), nor between diet with low glycemic index and MS risk (adjusted OR = 0.93, 95% CI: 0.60-1.42, p = 0.518). CONCLUSIONS: Mediterranean diet may exert a protective influence regarding the risk of subsequently developing MS compared with Western-style diet.

Influence of oral tobacco versus smoking on multiple sclerosis disease activity and progression.

We aimed to study the influence of smoking habits, exposure to passive smoking and snuff use on disease progression, cognitive performance and quality of life in patients with multiple sclerosis (MS). METHOD: Patients from two population-based case-control studies were categorised based on tobacco exposure at diagnosis and were followed up to 15 years post diagnosis through the Swedish MS registry (n=9089) regarding changes in Expanded Disability Status Scale (EDSS), Multiple Sclerosis Impact Scale 29 and Symbol Digit Modalities Test. We used linear mixed models to analyse long-term changes, and Cox regression models with 95% CI using 24-week confirmed disability worsening, reaching EDSS 3 and EDSS 4, respectively, physical and psychological worsening and cognitive disability worsening as end points. The influence of smoking cessation post diagnosis was also investigated. RESULTS: Compared with non-smokers, current smokers had a faster EDSS progression (ßcurrent smoking×time=0.03, 95% CI 0.02 to 0.04). A faster EDSS progression was also associated with passive smoking (ßcurrent passive smoking×time=0.04, 95% CI 0.03 to 0.06). Smoke exposure negatively impacted all secondary outcomes. Those who continued smoking had worse outcomes than those who stopped smoking post diagnosis. Snuff users had a more favourable EDSS progression, compared with never users. CONCLUSIONS: Our findings indicate that both smoking and passive smoking have a negative influence on MS and that smoking cessation post diagnosis may be an important secondary preventive measure. Snuff use was associated with slower disease progression, suggesting that nicotine replacement therapy could be an attractive way to increase the chance of quitting smoking among patients with MS.

Observed associations between indicators of socioeconomic status and risk of multiple sclerosis in Sweden are explained by a few lifestyle-related factors.

BACKGROUND AND PURPOSE: The association between socioeconomic status (SES) and the risk of multiple sclerosis (MS) is unclear. The aim was to study whether a potential association between indicators of SES and MS risk in Sweden is explained by lifestyle/environmental factors. METHODS: Using the Swedish MS registry and the Swedish patient registries, a register study was performed comprising all cases diagnosed with MS in Sweden between 1990 and 2018 (N = 24,729) and five randomly selected controls per case, matched by year and age at disease onset, sex and residential area at disease onset. Data from two matched case-control studies combined comprising data on environment/lifestyle factors (7193 cases, 9609 controls, inclusion period 2005-2018) were also utilized. For all participants, information regarding ancestry, formal education (available 1990-2018) and family income (available 1998-2018) was retrieved from the National Board of Health and Welfare. RESULTS: The registry study revealed no association between education and MS risk, whereas an income exceeding the upper quartile was associated with lower MS risk compared to having an income in the lowest quartile (odds ratio 0.86, 95% confidence interval 0.82-0.90). These findings were replicated in the crude analyses of the case-control study. However, after adjustment for confounding, no association was observed between income and risk of MS. CONCLUSIONS: Education and income were not associated with occurrence of MS after adjustment for a few lifestyle-related factors (smoking, alcohol consumption, body mass index and sun exposure habits), indicating that SES has no influence on MS risk besides its association with these lifestyle factors in the Swedish context.

Insufficient sleep during adolescence and risk of multiple sclerosis: results from a Swedish case-control study.

BACKGROUND: Shift work, which often results in sleep deprivation and circadian desynchrony, has been associated with increased risk of multiple sclerosis (MS). We aimed at studying the impact of sleep duration, circadian disruption and sleep quality on MS risk. METHODS: We used a Swedish population-based case-control study (2075 cases, 3164 controls). Aspects of sleep were associated with MS risk by calculating OR with 95% CIs using logistic regression models. RESULTS: Compared with sleeping 7-9 hours/night during adolescence, short sleep (<7 hours/night) was associated with increased risk of developing MS (OR 1.4, 95% OR 1.1-1.7). Similarly, subjective low sleep quality during adolescence increased the risk of subsequently developing MS (OR 1.5, 95% CI 1.3 to 1.9), whereas phase shift did not significantly influence the risk. Our findings remained similar when those who worked shifts were excluded. CONCLUSIONS: Insufficient sleep and low sleep quality during adolescence seem to increase the risk of subsequently developing MS. Sufficient restorative sleep at young age, needed for adequate immune functioning, may be a preventive factor against MS.

Disease Activity and Health-Related Quality of Life Among Patients With Rheumatoid Arthritis With Different Alcohol Consumption Habits.

OBJECTIVE: Multiple studies have found a relationship between alcohol consumption and disease activity in rheumatoid arthritis (RA), although reverse causation has been suggested to explain the association. We aimed to study the relationship between alcohol consumption and disease activity, disease progression, and health-related quality of life in patients with RA. METHODS: We followed up 1,228 patients with newly diagnosed RA from a population-based case-control study, Epidemiological Investigation of Rheumatoid Arthritis (EIRA). Drinkers and non-drinkers were compared to evaluate risk of unfavorable outcomes regarding disease activity and health-related quality of life. Odds ratios with 95% confidence intervals were calculated using logistic regression models. RESULTS: Non-drinkers at baseline had higher disease activity and estimated their pain as more severe compared to drinkers. At 1 year of follow-up, non-drinkers reported higher swollen and tender joint counts and experienced more pain and fatigue, lower global health scores, and lower health-related quality of life. The inverse relationship between alcohol consumption and RA-specific outcomes was also observed when comparing drinkers and non-drinkers who had not changed their alcohol consumption habits at or after the year of disease onset. Those who stopped drinking postbaseline experienced higher disease activity, more pain, and lower health-related quality of life at 1 year of follow-up, compared to drinkers, although there was no difference in disease activity at baseline between drinkers who continued versus discontinued drinking. Our findings argue against bias due to reverse causation. CONCLUSION: Alcohol consumption was associated with lower disease activity and higher health-related quality of life in RA patients in a dose-dependent manner.

Association between exposure to combustion-related air pollution and multiple sclerosis risk.

BACKGROUND: Smoking and occupational pulmonary irritants contribute to multiple sclerosis (MS) development. We aimed to study the association between ambient air pollution and MS risk and potential interaction with the human leukocyte antigen (HLA)-DRB1*15:01 allele. METHODS: Exposure to combustion-related air pollution was estimated as outdoor levels of nitrogen oxides (NOx) at the participants' residence locations, by spatially resolved dispersion modelling for the years 1990-18. Using two population-based case-control studies (6635 cases, 8880 controls), NOx levels were associated with MS risk by calculating odds ratios (OR) with 95% confidence intervals (CI) using logistic regression models. Interaction between high NOx levels and the HLA-DRB1*15:01 allele regarding MS risk was calculated by the attributable proportion due to interaction (AP). In addition, a register study was performed comprising all MS cases in Sweden who had received their diagnosis between 1993 and 2018 (n = 22 173), with 10 controls per case randomly selected from the National Population register. RESULTS: Residential air pollution was associated with MS risk. NOx levels (3-year average) exceeding the 90th percentile (24.6 µg/m3) were associated with an OR of 1.37 (95% CI 1.10-1.76) compared with levels below the 25th percentile (5.9 µg/m3), with a trend of increasing risk of MS with increasing levels of NOx (P <0.0001). A synergistic effect was observed between high NOx levels (exceeding the lower quartile among controls) and the HLA-DRB1*15:01 allele regarding MS risk (AP 0.26, 95% CI 0.13-0.29). CONCLUSIONS: Our findings indicate that moderate levels of combustion-related ambient air pollution may play a role in MS development.

Influence of Smoking on Disease Activity and Quality of Life in Patients With Rheumatoid Arthritis: Results From a Swedish Case-Control Study With Longitudinal Follow-Up.

OBJECTIVE: Inconclusive findings have been reported regarding the influence of smoking on disease outcomes in established rheumatoid arthritis (RA). This study was undertaken to investigate the influence of smoking habits on disease activity and health-related quality of life (HRQoL) in RA patients. METHODS: Patients with newly diagnosed RA (n = 1,531) from the population-based case-control Epidemiological Investigation of Rheumatoid Arthritis study were followed up for up to 3 years after recruitment. Using logistic regression models, the risks of unfavorable outcomes in patients with different smoking habits were compared using self-reported swollen and tender joint counts, the Short Form 36 health survey, the Health Assessment Questionnaire, and the Hospital Anxiety and Depression Scale by calculating odds ratios with 95% confidence intervals. RESULTS: At 1-year and 3-year follow-up, current smokers reported higher disease activity and lower HRQoL life compared to non-smokers, regarding both physical and mental aspects. Patients who stopped smoking within 1-year post-baseline had less disease activity measured as swollen joint counts at 1-year follow-up compared to those who continued smoking. Patients who stopped smoking after the 1-year follow-up had higher disease activity and lower HRQoL at baseline than smokers who did not quit, and late smoking cessation was not associated with more favorable outcomes compared to continued smoking. CONCLUSION: Current smoking is associated with increased disease activity and lower HRQoL among RA patients. Smoking cessation within the first year after baseline appears to have a favorable effect on disease activity.

Neither low social support nor low decision latitude at work is associated with disease remission among patients with rheumatoid arthritis: results from the Swedish EIRA study.

OBJECTIVES: To investigate the association between psychosocial vulnerability, defined as either low social support or low decision latitude at work, and disease remission at 3, 12, and 60 months in patients with rheumatoid arthritis (RA). METHODS: This cohort study included all patients enrolled in both the Swedish Epidemiological Investigation of Rheumatoid Arthritis (EIRA) 1996-2015 and the Swedish Rheumatology Quality Register (SRQ, n = 2820). Information on social support and decision latitude at work at RA diagnosis were identified from the EIRA questionnaire. Indexes for levels of social support and decision latitude at work, respectively, were calculated based on the questionnaire. Low social support and low decision latitude at work, respectively, were identified by a score in the lowest quartile and compared with the three other quartiles (not low). Disease-activity parameters were retrieved from SRQ at 3, 12, and 60 months. The associations between social support or decision latitude at work, respectively, and Disease Activity Score 28 joint count with C-reactive protein (DAS28-CRP) remission were analysed using logistic regression models adjusted for age, sex, smoking habits, alcohol habits, symptom duration, and educational level. RESULTS: Having low social support (n = 591) was not associated with DAS28-CRP remission at 3 (OR 0.93, 95% CI 0.74-1.16), 12 (OR 0.96, 95%CI 0.75-1.23), or 60 (OR 0.89, 95%CI 0.72-1.10) months compared to not low social support (n = 2209). No association was observed for low (n = 212) versus not low (n = 635) decision latitude at work and DAS28-CRP remission at 3 (OR 0.84, 95%CI 0.54-1.31), 12 (OR 0.81, 95%CI 0.56-1.16), or 60 (OR 1.37, 95%CI 0.94-2.01) months. CONCLUSION: In a country with general access to healthcare, psychosocial vulnerability does not influence the likelihood of achieving remission in early RA.

High antibody levels against human herpesvirus-6A interact with lifestyle factors in multiple sclerosis development.

BACKGROUND: Infection with human herpesvirus 6A (HHV-6A) has been suggested to increase multiple sclerosis (MS) risk. However, potential interactions between HHV-6A and environmental/lifestyle risk factors for MS have not previously been studied. METHODS: We used two Swedish population-based case-control studies comprising 5993 cases and 5995 controls. Using logistic regression models, subjects with different HHV-6A antibody levels, environmental exposures, and lifestyle habits were compared regarding MS risk, by calculating odds ratios (ORs) with 95% confidence intervals (CIs). Potential interactions between high HHV-6A antibody levels and common environmental exposures and lifestyle factors were evaluated on the additive scale. RESULTS: High HHV-6A antibody levels were associated with increased risk of developing MS (OR = 1.5, 95% CI = 1.4-1.6). Regarding MS risk, significant interactions were observed between high HHV-6A antibody levels and both smoking (attributable proportion (AP) = 0.2, 95% CI = 0.1-0.3), low ultraviolet radiation (UVR) exposure (AP = 0.3, 95% CI = 0.1-0.4), and low vitamin D levels (AP = 0.3, 95% CI = 0.0-0.6). CONCLUSION: High HHV-6A antibody levels are associated with increased MS risk and act synergistically with common environmental/lifestyle risk factors for MS. Further research is needed to investigate potential mechanisms underlying the interactions presented in this study.

The increased risk of multiple sclerosis associated with HLA-DRB1*15:01 and smoking is modified by alcohol consumption.

Previous studies have observed an inverse association between alcohol consumption and multiple sclerosis (MS) risk. We aimed to investigate possible interactions between alcohol consumption, MS-associated human leukocyte antigen (HLA) genes and smoking regarding MS risk. We used a Swedish population-based case-control study (2059 incident cases, 2887 controls) matched by age, sex, and residential area. Subjects with different genotypes and alcohol consumption habits were compared regarding MS risk, by calculating odds ratios with 95% confidence intervals using logistic regression models. Interaction on the additive scale between non-drinking and both genotype and smoking were assessed by calculating the attributable proportion due to interaction (AP). There was a dose-dependent inverse association between alcohol consumption and MS risk (p for trend < 0.0001). A potentiating effect was observed between non-drinking and presence of DRB1*15:01 (AP 0.3, 95% CI 0.2-0.5) which was of similar magnitude irrespective of smoking habits. Non-drinking also interacted with smoking to increase MS risk (AP 0.2, 95% CI 0.06-0.4). Non-drinking interacts with DRB1*15:01 and smoking to increase the risk of MS. Better understanding of the mechanisms behind our findings may help to define ways to achieve protection against MS by other means than alcohol consumption.