Latitude continues to be significantly associated with the prevalence of multiple sclerosis: an updated meta-analysis.

OBJECTIVES: Previous studies have demonstrated a strong latitudinal gradient in multiple sclerosis (MS) prevalence. Herein, we present a meta-analysis of the latitudinal gradient of MS prevalence including studies published since our 2011 review, seeking to assess the latitudinal gradient and whether it has changed since our previous analysis. METHODS: Studies published up to December 2018 were located via Embase, Web of Knowledge and PubMed, using standardised search terms; data were extracted from peer-reviewed studies and these studies added to those from our previous analysis. Where age-specific data were available, prevalence estimates were age-/sex-standardised to the 2009 European population. Prevalence estimates were adjusted for study prevalence year and ascertainment methods. The latitudinal association with MS prevalence was assessed by meta-regression. RESULTS: A total of 94 studies met inclusion criteria, yielding 230 new prevalence points and 880 altogether with those from the prior study. There was a significant positive gradient in time-corrected MS prevalence with increasing latitude (5.27/100 000 per degree latitude), attenuating slightly to 4.34/100 000 on age-standardisation, these associations persisting on adjustment for ascertainment method. Of note, the age-standardised gradient was consistently significantly enhanced from our previous study, regardless of whether it was as-measured, time-corrected or adjusted for ascertainment methods. Certain areas, such as the Scandinavian and Atlantic Coast/Central Europe regions, showed changes in MS prevalence gradient over time, but other regional gradients were similar. CONCLUSIONS: This new meta-analysis confirms that MS prevalence is still strongly positively associated with increasing latitude and that the gradient is increasing, suggesting that potentially modifiable environmental factors, such as sun exposure, are still strongly associated with MS risk.

Lipid-related genetic polymorphisms significantly modulate the association between lipids and disability progression in multiple sclerosis.

OBJECTIVE: To investigate whether lipid-related or body mass index (BMI)-related common genetic polymorphisms modulate the associations between serum lipid levels, BMI and disability progression in multiple sclerosis (MS). METHODS: The association between disability progression (annualised Expanded Disability Status Scale (EDSS) change over 5 years, ΔEDSS) and lipid-related or BMI-related genetic polymorphisms was evaluated in a longitudinal cohort (n=184), diagnosed with MS. We constructed a cumulative genetic risk score (CGRS) of associated polymorphisms (p<0.05) and examined the interactions between the CGRS and lipid levels (measured at baseline) in predicting ΔEDSS. All analyses were conducted using linear regression. RESULTS: Five lipid polymorphisms (rs2013208, rs9488822, rs17173637, rs10401969 and rs2277862) and one BMI polymorphism (rs2033529) were nominally associated with ΔEDSS. The constructed lipid CGRS showed a significant, dose-dependent association with ΔEDSS (ptrend=1.4×10-6), such that participants having ≥6 risk alleles progressed 0.38 EDSS points per year faster compared with those having ≤3. This CGRS model explained 16% of the variance in ΔEDSS. We also found significant interactions between the CGRS and lipid levels in modulating ΔEDSS, including high-density lipoprotein (HDL; pinteraction=0.005) and total cholesterol:high-density lipoprotein ratio (TC:HDL; pinteraction=0.030). The combined model (combination of CGRS and the lipid parameter) explained 26% of the disability variance for HDL and 27% for TC:HDL. INTERPRETATION: In this prospective cohort study, both lipid levels and lipid-related polymorphisms individually and jointly were associated with significantly increased disability progression in MS. These results indicate that these polymorphisms and tagged genes might be potential points of intervention to moderate disability progression.

Complementary and alternative treatments of multiple sclerosis: a review of the evidence from 2001 to 2016.

People with multiple sclerosis (PwMS) commonly use complementary and alternative medicines (CAM), but an understanding of their efficacy is lacking. Here, we quantitatively review the class I and class II studies of treatment efficacy for multiple sclerosis from January 2001 to January 2017, in order to assess the modern evidence for CAM use. The 38 studies included in this review are divided across five CAM types (cannabis, diet, exercise, psychological approaches and other). We found little evidence to support CAM efficacy. The studies contained little replication in intervention, primary outcomes or study design. Six of 16 CAMs included in this review were only researched in a single study. Future work in this area should build consensus around study methodologies and primary outcomes.

Effects of multiple sclerosis disease-modifying therapies on employment measures using patient-reported data.

BACKGROUND: The direct comparative evidence on treatment effects of available multiple sclerosis (MS) disease-modifying therapies (DMTs) is limited, and few studies have examined the benefits of DMTs on employment outcomes. We compared the effects of DMTs used in the previous 5 years on improving the work attendance, amount of work and work productivity of people with MS. METHODS: The Australian MS Longitudinal Study collected data from participants on DMTs usage from 2010 to 2015 and whether DMTs contributed to changes in employment outcomes. We classified 11 DMTs into three categories based on their clinical efficacy (ß-interferons and glatiramer acetate as category 1; teriflunomide and dimethyl fumarate as category 2; fingolimod, natalizumab, alemtuzumab and mitoxantrone as category 3). Each DMT used by a participant was treated as one observation and analysed by log-multinomial regression. RESULTS: Of the 874 participants included, 1384 observations were generated. Those who used category 3 (higher efficacy) DMTs were 2-3 times more likely to report improvements in amount of work, work attendance and work productivity compared with those who used category 1 (classical injectable) DMTs. Natalizumab was associated with superior beneficial effects on patient-reported employment outcomes than fingolimod (RR=1.76, 95% CI 1.02 to 3.03 for increased work attendance and RR=1.46, 95% CI 1.02 to 2.10 for increased work productivity). CONCLUSIONS: Those using the higher efficacy (category 3) DMTs, particularly fingolimod and natalizumab, reported significant increases in amount of work, work attendance and work productivity, suggesting they have important beneficial effects on work life in people with MS.

Novel modulating effects of PKC family genes on the relationship between serum vitamin D and relapse in multiple sclerosis.

BACKGROUND: The interplay between genes and environmental factors on multiple sclerosis (MS) clinical course has been little studied. METHODS: We conducted a prospective cohort study of 141 participants with relapsing-remitting MS (RRMS) and genotype data followed from 2002 to 2005 and examined genes in the vitamin D metabolism and vitamin D receptor (VDR)/retinoid X receptor (RXR) transcription factor formation pathway. Gene-vitamin D interactions and the genetic predictors of relapse were assessed using survival analysis. Genetic predictors of 25-hydroxyvitamin D (25(OH)D) were evaluated by multilevel mixed-effects linear regression. Significance threshold was adjusted by Bonferroni correction for the number of genes evaluated. RESULTS: The relationship between 25(OH)D and hazard of relapse was significantly different for different alleles of two intronic single nucleotide polymorphisms (SNPs) (rs908742 in PRKCZ and rs3783785 in PRKCH) in the protein kinase C (PKC) family genes (p(interaction)=0.001, p(adj)=0.021, respectively). Two other intronic SNPs (rs1993116 in CYP2R1and rs7404928 in PRKCB) were significantly associated with lower levels of 25(OH)D (p(interaction)=0.001, p(adj)=0.021, respectively). A cumulative effect of multiple 'risk' genotypes on 25(OH)D levels and hazard of relapse was observed for the significant SNPs (p(trend)=7.12×10(-6) for 25(OH)D levels, p(trend)=8.86×10(-6) for hazard of relapse). CONCLUSIONS: Our data support the hypothesis that gene-vitamin D interactions may influence MS clinical course and that the PKC family genes may play a role in the pathogenesis of MS relapse through modulating the association between 25(OH)D and relapse.

Higher consumption of ultra-processed foods and increased likelihood of central nervous system demyelination in a case-control study of Australian adults.

BACKGROUND: Consumption of ultra-processed foods (UPFs) has been linked to risk of chronic diseases, with scant evidence in relation to multiple sclerosis (MS). METHODS: We tested associations between UPF consumption and likelihood of a first clinical diagnosis of central nervous system demyelination (FCD) (267 cases, 508 controls), a common precursor to MS. We used data from the 2003-2006 Ausimmune Study and logistic regression with full propensity score matching for age, sex, region of residence, education, smoking history, body mass index, physical activity, history of infectious mononucleosis, dietary misreporting, and total energy intake. RESULTS: Higher UPF consumption was statistically significantly associated with an increased likelihood of FCD (adjusted odds ratio = 1.08; 95% confidence interval = 1.0,1.15; p = 0.039), representing an 8% increase in likelihood of FCD per one energy-adjusted serving/day of UPFs. CONCLUSION: Higher intakes of UPF were associated with increased likelihood of FCD in this Australian cohort. Nutrition education and awareness of healthy eating patterns may benefit those at high risk of FCD.

Alcohol intake is associated with a decreased risk of developing primary biliary cholangitis.

BACKGROUND: Primary biliary cholangitis (PBC) is a chronic progressive liver disease of unknown aetiology characterised by immune-mediated destruction of small and medium-sized intrahepatic bile ducts. There are few well-established risk factors and epidemiological studies are needed to further evaluate the pathogenesis of the disease. AIM: To evaluate the relationship between alcohol intake, smoking and marijuana use with PBC development. METHODS: We conducted a prevalent case control study of 200 cases and 200 age (within a five year age band) and sex-matched controls, identified from the Victorian PBC prevalence study. We assessed lifetime alcohol intake and smoking behaviour (both tobacco and marijuana) prior to PBC onset and used conditional logistic regression for analyses. RESULTS: Alcohol intake consistently showed a dose-dependent inverse association with case status, and this was most substantial for 21-30 years and 31-40 years (P trend < 0.001). Smoking was associated with PBC, with a stronger association with a longer duration of smoking [e.g., adjusted OR 2.27 (95%CI: 1.12- 4.62) for those who had smoked for 20-35 years]. There was no association between marijuana use and PBC. CONCLUSION: Alcohol appears to have an inverse relationship with PBC. Smoking has been confirmed as an environmental risk factor for PBC. There was no association between marijuana use and PBC.

Human leukocyte antigen-DR15, low infant sibling exposure and multiple sclerosis: gene-environment interaction.

The risk for development of multiple sclerosis has been associated with human leukocyte antigen-DRB1*1501-DQB1*0602 (HLA-DR15) genotype, low infant sibling exposure, and high Epstein-Barr nuclear antigen IgG levels. In a population-based case-control study (Tasmania, Australia), we found that the combined effect of HLA-DR15 positivity and low infant sibling exposure on multiple sclerosis (odds ratio, 7.88; 95% confidence interval, 3.43-18.11) was 3.9-fold greater than expected (test for interaction, p = 0.019) This interaction was observed irrespective of Epstein-Barr nuclear antigen IgG levels. This suggests that immune mechanisms involving HLA class II molecules are susceptible to modulation in early life. Ann Neurol 2009;66:261-265 ANN NEUROL 2010;67:259-263.

The role of latitude, ultraviolet radiation exposure and vitamin D in childhood asthma and hayfever: an Australian multicenter study.

Observations of increasing allergy prevalence with decreasing distance from the Equator and positive associations with ambient ultraviolet radiation have contributed to a growing interest in the possible role of vitamin D in the etiology of allergy. The aims of this study were to describe any latitudinal variation in the prevalence of childhood allergy in Australia and to evaluate, in parallel, the individual associations between ultraviolet radiation (UVR)- and vitamin D-related measures and hayfever asthma and both conditions. Participants were population-based controls who took part in a multicenter case-control study, aged 18-61 yr and resident in one of four study regions ranging in latitude from 27°S to 43°S. Data were derived from a self-administered questionnaire, interview and examination by a research officer and biologic sampling. Latitude and longitude coordinates were geocoded from participants' residential locations and climatic data were linked to postcodes of current residence. Stored serum was analyzed for 25-hydroxyvitamin D concentrations and silicone rubber casts of the skin were used as an objective measure of cumulative actinic damage. There was an inverse latitude gradient for asthma (a 9% decrease per increasing degree of latitude); however, this pattern did not persist after adjusting for average daily temperature. There was no association between any of the UVR- or vitamin D-related measures and childhood asthma, but greater time in the sun in winter between the ages 6-15 yr was associated with an increase in the odds of having hayfever [adjusted odds ratios (OR) 1.29; 95% CI 1.01-1.63]. Oral supplementation with cod liver oil in childhood increased the odds of a history of having both asthma and hayfever (2.87; 1.00-8.32). Further investigation of the possible role of early vitamin D supplementation in the development of allergy is warranted. Our results also suggest that solar exposure during childhood may be important in allergic sensitization. Plausible explanations, including biologic mechanisms, exist for both observations.

Latitudinal variation in incidence and type of first central nervous system demyelinating events.

Increasing prevalence and variable geographic patterns of occurrence of multiple sclerosis suggest an environmental role in causation. There are few descriptive, population-level, data on whether such variability applies to first demyelinating events (FDEs). We recruited 216 adults (18-59 years), with a FDE between 1 November 2003 and 31 December 2006 in a multi-center incident case-control study in four locations on the south-eastern and eastern seaboard of Australia, spanning latitudes 27 degrees south to 43 degrees south. Population denominators were obtained from the Australian Bureau of Statistics censuses of 2001 and 2006. Age and sex adjusted FDE incidence rates increased by 9.55% (95% confidence interval (CI) 7.37-11.78, p < 0.001) per higher degree of latitude. The incidence rate gradient per higher degree of latitude varied by gender (male: 14.69% (95% CI 9.68-19.94, p < 0.001); female 8.13% (95% CI 5.69-10.62, p < 0.001)); and also by the presenting FDE type: optic neuritis 11.39% (95% CI 7.15-15.80, p < 0.001); brainstem/cerebellar syndrome 9.47% (95% CI 5.18-13.93, p < 0.001); and spinal cord syndrome 5.36% (95% CI 1.78-9.06, p = 0.003). Differences in incidence rate gradients were statistically significant between males and females (p = 0.02) and between optic neuritis and spinal cord syndrome (p = 0.04). The male to female ratio varied from 1 : 6.7 at 27 degrees south to 1 : 2.5 at 43 degrees south. The study establishes a positive latitudinal gradient of FDE incidence in Australia. The latitude-related factor(s) influences FDE incidence variably according to subtype and gender, with the strongest influence on optic neuritis presentations and for males. These descriptive case analyses show intriguing patterns that could be important for understanding the etiology of multiple sclerosis.

CTLA-4 and multiple sclerosis: the A49G single nucleotide polymorphism shows no association with multiple sclerosis in a Southern Australian population.

Multiple sclerosis (MS) is a chronic autoimmune disorder that causes inflammatory demyelination and axonal damage in the central nervous system (CNS). We have investigated whether the A49G single nucleotide polymorphism (SNP) genotype of the CTLA-4 gene influenced the development of MS in Southern Australians as well as the interaction of this SNP with the DRB1*15 haplotype. There were no significant (P<0.05) associations between the A49G genotype and risk of MS, either before or after stratification for presence of the DR15 haplotype.

Monthly ambient sunlight, infections and relapse rates in multiple sclerosis.

BACKGROUND: Monthly variation in multiple sclerosis (MS) relapses has been found. The relationship between seasonal environmental factors, infections, serum vitamin D [25(OH)D] and MS relapses is undetermined. METHODS: We prospectively followed a population-based cohort of relapsing-remitting (RR) MS patients in Southern Tasmania for a mean 2.3 years (January 2002-April 2005). Associations between monthly ambient environmental factors, estimated serum 25(OH)D, upper respiratory tract (URT) infections and relapse rates were examined using weighted Pearson's correlation and linear regression. RESULTS: Of 199 definite MS patients, 142 had RRMS. The lowest relapse rate of 0.5 per 1,000 days (95% CI: 0.2-1.3) occurred in February (mid-late summer) versus the March-January RR of 1.1 per 1,000 days (95% CI: 0.9-1.3; p = 0.018, weighted regression). Monthly relapse rates correlated with: (1) prior erythemal ultraviolet radiation (EUV): lagged 1.5 months, r = -0.32, p = 0.046; (2) URT infection rate: no lag, r = 0.39, p = 0.014; (3) 25(OH)D: no lag, r = -0.31, p = 0.057. The association between URT infections and relapses was reduced after adjustment for monthly EUV. CONCLUSIONS: Relapse rates were inversely associated with EUV and serum 25(OH)D levels and positively associated with URT infections. The demonstrated lag between EUV but not 25(OH)D and relapse rates is consistent with a role for EUV-generated 25(OH)D in the alteration of relapse rates. Future work on the association between URT infections and relapses should be considered in the context of ultraviolet radiation and vitamin D.

The multiple sclerosis risk allele within the AHI1 gene is associated with relapses in children and adults.

BACKGROUND: While common variant non-HLA (human leukocyte antigen) alleles have been associated with MS risk, their role in disease course is less clear. We sought to determine whether established multiple sclerosis (MS) genetic susceptibility factors are associated with relapse rate in children and an independent cohort of adults with MS. METHODS: Genotyping was performed for 182 children with MS or clinically isolated syndrome with high risk for MS from two Pediatric MS Centers. They were prospectively followed for relapses. Fifty-two non-HLA MS susceptibility single nucleotide polymorphisms (SNPs) were evaluated for association with relapse rate. Cox regression models were adjusted for sex, genetic ancestry, disease-modifying therapy (DMT), 25-OH vitamin D level and HLA-DRB1*15:01/03 status. Investigation of pediatric subject SNP results was performed using a second cohort of 141 adult MS subjects of Northern European ancestry from the Southern Tasmanian Multiple Sclerosis Longitudinal Study. RESULTS: For pediatric subjects, 408 relapses were captured over 622 patient-years of follow-up. Four non-HLA risk SNPs (rs11154801, rs650258, rs12212193, rs2303759) were associated with relapses (p < 0.01) in the pediatric subjects. After adjustment for genetic ancestry, sex, age, vitamin D level, DMT use and HLA-DRB1*15 status, having two copies of the MS risk allele within AHI1 (rs11154801) was associated with increased relapses among children (HR = 1.75,95%CI = 1.18-2.48, p = 0.006) and this result was also observed among adults (HR = 1.81,95%CI = 1.05-3.03, p = 0.026). CONCLUSIONS: Our results suggest that the MS genetic risk variant within the gene AHI1 may contribute to disease course in addition to disease susceptibility.

The high prevalence of vitamin D insufficiency across Australian populations is only partly explained by season and latitude.

BACKGROUND: Inadequate sun exposure and dietary vitamin D intake can result in vitamin D insufficiency. However, limited data are available on actual vitamin D status and predictors in healthy individuals in different regions and by season. METHODS: We compared vitamin D status [25-hydroxyvitamin D; 25(OH)D] in people < 60 years of age using data from cross-sectional studies of three regions across Australia: southeast Queensland (27 degrees S; 167 females and 211 males), Geelong region (38 degrees S; 561 females), and Tasmania (43 degrees S; 432 females and 298 males). RESULTS: The prevalence of vitamin D insufficiency (

Multiple sclerosis: a haplotype association study.

Results are presented from a genomewide haplotype association study on multiple sclerosis (MS) cases from Tasmania, an island state of Australia. Cases were ascertained on strict clinical and radiological grounds and on the fact that they had at least one grandparent born in the state. This enriched for early settler chromosomes among present day Tasmanians with MS and increased the chances of finding common haplotype sharing at disease predisposition loci in distant relatives sharing common ancestral haplotypes. Four-to-five close relatives were also collected for each of 170 cases and 105 population-based controls. All were genotyped at a 5cM resolution, haplotypes reconstructed and sharing estimated using an empirical approach based on sorting haplotypes to find the most common at each locus and then generating a test statistic for excess sharing in the cases based on permutation testing. Five initial loci were found where there was an excess sharing in the cases. These were fine-mapped with 10-12 additional markers. Only loci on chromosomes 6 and 10 remained after fine mapping. These loci demonstrate an increase in sharing of multi-marker haplotypes in MS cases compared to both population control transmitted haplotypes and case non-transmitted haplotypes.

The co-occurrence of multiple sclerosis and type 1 diabetes: shared aetiologic features and clinical implication for MS aetiology.

We reviewed the evidence for the co-occurrence of type 1 diabetes mellitus (T1D) and multiple sclerosis (MS), and assessed the clinical significance of this association and the shared aetiological features of the two diseases. T1D and MS contribute considerably to the burden of autoimmune diseases in young adults. The co-occurrence of MS and T1D has been reported by a number of studies, suggesting that the two conditions share one or more aetiological components. Both conditions have been associated with distinct human leukocyte antigen (HLA) haplotypes but share a number of similarities in clinical, epidemiological and immunological features, leading to suggestions of possible common mechanisms of development. While underlying genetic factors may be important for the co-occurrence of both conditions, some evidence suggests that environmental factors such as vitamin D deficiency may also modulate an individual's risk for the development of both conditions. Evidence on whether the co-occurrence of the two autoimmune conditions will affect the disease course and severity of MS is merely absent. Further studies need to be conducted to ascertain whether the neuropathology associated with T1D might influence the disease course and contribute to the severity of MS.

Misclassification due to body hair and seasonal variation on melanin density estimates for skin type using spectrophotometry.

Recent advances have enabled quite accurate estimations of cutaneous melanin density by spectrophotometry using reflectance of light at wavelengths 400 and 420 nm. Our purpose was to assess the effect of body hair and seasonal variation at the upper inner arm and buttock on measurements of melanin density. We estimated melanin density of 104 volunteers at 3-monthly intervals over 12 months both before and after shaving. Removing body hair at the upper inner arm had no effect, but substantially reduced melanin estimates at the buttock in men. Significant seasonal variation was only observed at the upper inner arm, with highest readings in summer-autumn. In case-control studies, misclassification due to body hair at the buttock and seasonal variation at the upper inner arm could affect the observed odds ratio substantially. However, both sources of error can be reduced by careful attention to key aspects of study design.

Vascular comorbidities in the onset and progression of multiple sclerosis.

Vascular comorbidities are common in the general population and are associated with adverse health outcomes. In people with multiple sclerosis (MS), an increasing amount of evidence suggests that vascular comorbidities are also common, but an association with MS risk and disability has not been conclusively established. This review aims to critically examine published data on the relationship between vascular comorbidities (including vascular risk factors) and MS. The evidence suggests an increased risk of MS in people with a high BMI during childhood or adolescence but not adulthood. People with established MS appear to have a slightly increased risk of cardiovascular disease and a greater proportion of people with MS die from cardiovascular disease, which has important implications for clinicians trying to identify risk factors for cardiovascular disease and reviewing treatment options. In relation to whether vascular comorbidities influence MS clinical disability or other aspects of the disease course, the key finding was that having type-2-diabetes, hypertension, dyslipidaemia or peripheral vascular disease at any point in the disease course may be associated with a greater progression in disability. Additionally, a negative effect of high cholesterol and triglycerides and a positive effect of higher HDL (high density lipoprotein) levels on acute inflammatory activity were observed on magnetic resonance imaging. The results of the published clinical trials of statins as an intervention in MS were however conflicting and care needs to be taken when treating people with MS with statins. Taken together, the literature seems to indicate a potential association of vascular comorbidities with MS risk and disability, but the number of prospective studies was sparse, thus precluding ascription of causality. We therefore recommend that future studies of the frequency and effects of vascular comorbidities on MS risk and disability should be prospective and objective where relevant.

Multiple sclerosis susceptibility-associated SNPs do not influence disease severity measures in a cohort of Australian MS patients.

Recent association studies in multiple sclerosis (MS) have identified and replicated several single nucleotide polymorphism (SNP) susceptibility loci including CLEC16A, IL2RA, IL7R, RPL5, CD58, CD40 and chromosome 12q13-14 in addition to the well established allele HLA-DR15. There is potential that these genetic susceptibility factors could also modulate MS disease severity, as demonstrated previously for the MS risk allele HLA-DR15. We investigated this hypothesis in a cohort of 1006 well characterised MS patients from South-Eastern Australia. We tested the MS-associated SNPs for association with five measures of disease severity incorporating disability, age of onset, cognition and brain atrophy. We observed trends towards association between the RPL5 risk SNP and time between first demyelinating event and relapse, and between the CD40 risk SNP and symbol digit test score. No associations were significant after correction for multiple testing. We found no evidence for the hypothesis that these new MS disease risk-associated SNPs influence disease severity.

Smoking is associated with progressive disease course and increased progression in clinical disability in a prospective cohort of people with multiple sclerosis.

BACKGROUND: Multiple sclerosis has a variable disease course. The contribution of modifiable lifestyle factors to disease course has not been well studied, although one cohort has reported that smoking is associated with conversion to secondary progressive MS course and another that smoking is not. METHODS: We conducted a prospective cohort study of people with MS in Southern Tasmania from 2002 to 2004 with 78% (203/259) of eligible participating and 198 with one or more reviews and confirmed MS. The cohort had a high retention rate (90% (183/203)). The median follow-up time was 909 days. Smoking data were collected at baseline and six-monthly reviews. Clinical disability assessments were conducted annually in conjunction with a real time clinical notification system for relapses. A repeated measures analysis and other statistical methods were used. RESULTS: Cumulative pack-years (p-y) smoked after cohort entry was associated with an increase in longitudinal MSSS (p < 0.001). Relative to the 0 pack years (p-y) category (in the year prior to the MSSS measure) those in the 0 to 1 p-y category had an adjusted mean difference in MSSS of 0.34 (95% CI 0.28, 0.66); those in the 1 to 2 p-y category had a 0.41 (95% CI -0.03, 0.85) increase; and those in the 2 or more p-y category had a 0.99 (95% CI 0.41, 1.58) increase in MSSS. Similar results were found using a variety of statistical approaches or EDSS as a clinical outcome. Smoking during the cohort period was not associated with relapse (cumulative pack years smoked after cohort entry, HR 0.94 (0.69, 1.26) per pack year). CONCLUSION: A better understanding of the mechanisms underlying smoking and multiple sclerosis, particularly progressive forms of the disease, may provide new insights for the eventual goal of better treatment and prevention of multiple sclerosis.