Little evidence for an effect of smoking on multiple sclerosis risk: A Mendelian Randomization study

Lifetime exposure to smoking and substance abuse may be associated with late-onset multiple sclerosis: a population-based case-control study

BACKGROUND

Late-onset multiple sclerosis (LOMS), defined as the development of MS after the age of 50, has shown a substantial surge in incidence rates and is associated with more rapid progression of disability. Besides, studies have linked tobacco smoking to a higher chance of MS progression. However, the role of smoking on the risk of developing LOMS remains unclear. This study aims to evaluate the possible association between lifetime exposure to cigarette and waterpipe smoking, drug abuse, and alcohol consumption and the risk of LOMS.

METHODS

This population-based case-control study involved LOMS cases and healthy sex and age-matched controls from the general population in Tehran, Iran. The primary data for confirmed LOMS cases were obtained from the nationwide MS registry of Iran (NMSRI), while supplementary data were collected through telephone and on-site interviews. Predesigned questionnaire for multinational case-control studies of MS environmental risk factors was used to evaluate the LOMS risk factors. The study employed Likelihood ratio chi-square test to compare qualitative variables between the two groups and utilized two independent sample t-test to compare quantitative data. Adjusted odds ratio (AOR) for age along with 95% confidence intervals (CI) were calculated using matched logistic regression analysis in SPSS 23.

RESULTS

Totally, 83 LOMS cases and 207 controls were included in the analysis. The female to male ratio in the cases was 1.5: 1. The mean ± SD age of 83 cases and 207 controls was 61.14 ± 5.38) and 61.51 ± 7.67 years, respectively. The mean ± SD expanded disability status scale (EDSS) score was 3.68 ± 2.1. Although the results of waterpipe exposure had no significant effect on LOMS development (P-value: 0.066), ever cigarette-smoked participants had a significantly higher risk of developing LOMS than those who never smoked (AOR: 2.57, 95% CI: 1.44-4.60). Furthermore, people with a history of smoking for more than 20 years had 3.45 times the odds of developing MS than non-smokers. Drug and alcohol abuse were both associated with LOMS in our study; of which opioids (AOR: 5.67, 95% CI: 2.05-15.7), wine (AOR: 3.30, 95% CI: 1.41-7.71), and beer (AOR: 3.12, 95% CI: 1.45-6.69) were found to pose the greatest risk of LOMS, respectively.

CONCLUSION

For the first time, we identified smoking, drug, and alcohol use as potential risk factors for LOMS development. According to the global increase in cigarette smoking and alcohol use, these findings highlight the importance of conducting interventional approaches for prevention.

An atlas of genetic determinants of forearm fracture

Osteoporotic fracture is among the most common and costly of diseases. While reasonably heritable, its genetic determinants have remained elusive. Forearm fractures are the most common clinically recognized osteoporotic fractures with a relatively high heritability. To establish an atlas of the genetic determinants of forearm fractures, we performed genome-wide association analyses including 100,026 forearm fracture cases. We identified 43 loci, including 26 new fracture loci. Although most fracture loci associated with bone mineral density, we also identified loci that primarily regulate bone quality parameters. Functional studies of one such locus, at TAC4, revealed that Tac4-/- mice have reduced mechanical bone strength. The strongest forearm fracture signal, at WNT16, displayed remarkable bone-site-specificity with no association with hip fractures. Tall stature and low body mass index were identified as new causal risk factors for fractures. The insights from this atlas may improve fracture prediction and enable therapeutic development to prevent fractures.

A systematic review of Mendelian randomization studies on multiple sclerosis

Mendelian randomization (MR) is a powerful approach for assessing the causal effect of putative risk factors on an outcome, using genetic variants as instrumental variables. The methodology and application developed in the framework of MR have been dramatically improved, taking advantage of the many public genome-wide association study (GWAS) data. The availability of summary-level data allowed to perform numerous MR studies especially for complex diseases, pinpointing modifiable exposures causally related to increased or decreased disease risk. Multiple sclerosis (MS) is a complex multifactorial disease whose aetiology involves both genetic and non-genetic risk factors and their interplay. Previous observational studies have revealed associations between candidate modifiable exposures and MS risk; although being prone to confounding, and reverse causation, these studies were unable to draw causal conclusions. MR analysis addresses the limitations of observational studies and allows to establish reliable and accurate causal conclusions. Here, we systematically reviewed the studies evaluating the causal effect, through MR, of genetic and non-genetic exposures on MS risk. Among 107 papers found, only 42 were eligible for final evaluation and qualitative synthesis. We found that, above all, low vitamin D levels and high adult body mass index (BMI) appear to be uncontested risk factors for increased MS risk.

Mendelian randomization as a tool to gain insights into the mosaic causes of autoimmune diseases

Autoimmune diseases (ADs) are a broad range of disorders which are characterized by long-term inflammation and tissue damage arising from an immune response against one's own tissues. It is now widely accepted that the causes of ADs include environmental factors, genetic susceptibility and immune dysregulation. However, the exact etiology of ADs has not been fully elucidated to date. Because observational studies are plagued by confounding factors and reverse causality, no firm conclusions can be drawn about the etiology of ADs. Over the years, Mendelian randomization (MR) analysis has come into focus, offering unique perspectives and insights into the etiology of ADs and promising the discovery of potential therapeutic interventions. In MR analysis, genetic variation (alleles are randomly dispensed during meiosis, usually irrespective of environmental or lifestyle factors) is used instead of modifiable exposure to explore the link between exposure factors and disease or other outcomes. Therefore, MR analysis can provide a valuable method for exploring the causal relationship between different risk factors and ADs when its inherent assumptions and limitations are fully considered. This review summarized the recent findings of MR in major ADs, including systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), multiple sclerosis (MS), and type 1 diabetes mellitus (T1DM), focused on the effects of different risk factors on ADs risks. In addition, we also discussed the opportunities and challenges of MR methods in ADs research.

Assessment of the genetic and clinical determinants of hip fracture risk: Genome-wide association and Mendelian randomization study

Hip fracture is the clinically most important fracture, but the genetic architecture of hip fracture is unclear. Here, we perform a large-scale hip fracture genome-wide association study meta-analysis and Mendelian randomization study using five cohorts from European biobanks. The results show that five genetic signals associate with hip fractures. Among these, one signal associates with falls, but not with bone mineral density (BMD), while four signals are in loci known to be involved in bone biology. Mendelian randomization analyses demonstrate a strong causal effect of decreased femoral neck BMD and moderate causal effects of Alzheimer's disease and having ever smoked regularly on risk of hip fractures. The substantial causal effect of decreased femoral neck BMD on hip fractures in both young and old subjects and in both men and women supports the use of change in femoral neck BMD as a surrogate outcome for hip fractures in clinical trials.

Towards a global view of multiple sclerosis genetics

Multiple sclerosis (MS) is a neuroimmunological disorder of the CNS with a strong heritable component. The genetic architecture of MS susceptibility is well understood in populations of European ancestry. However, the extent to which this architecture explains MS susceptibility in populations of non-European ancestry remains unclear. In this Perspective article, we outline the scientific arguments for studying MS genetics in ancestrally diverse populations. We argue that this approach is likely to yield insights that could benefit individuals with MS from all ancestral groups. We explore the logistical and theoretical challenges that have held back this field to date and conclude that, despite these challenges, inclusion of participants of non-European ancestry in MS genetics studies will ultimately be of value to all patients with MS worldwide.

Genetics of multiple sclerosis: lessons from polygenicity

Large-scale mapping studies have identified 236 independent genetic variants associated with an increased risk of multiple sclerosis. However, none of these variants are found exclusively in patients with multiple sclerosis. They are located throughout the genome, including 32 independent variants in the MHC and one on the X chromosome. Most variants are non-coding and seem to act through cell-specific effects on gene expression and splicing. The likely functions of these variants implicate both adaptive and innate immune cells in the pathogenesis of multiple sclerosis, provide pivotal biological insight into the causes and mechanisms of multiple sclerosis, and some of the variants implicated in multiple sclerosis also mediate risk of other autoimmune and inflammatory diseases. Genetics offers an approach to showing causality for environmental factors, through Mendelian randomisation. No single variant is necessary or sufficient to cause multiple sclerosis; instead, each increases total risk in an additive manner. This combined contribution from many genetic factors to disease risk, or polygenicity, has important consequences for how we interpret the epidemiology of multiple sclerosis and how we counsel patients on risk and prognosis. Ongoing efforts are focused on increasing cohort sizes, increasing diversity and detailed characterisation of study populations, and translating these associations into an understanding of the biology of multiple sclerosis.

Neuroinflammation in neurodegeneration via microbial infections

Recent epidemiological studies show a noticeable correlation between chronic microbial infections and neurological disorders. However, the underlying mechanisms are still not clear due to the biological complexity of multicellular and multiorgan interactions upon microbial infections. In this review, we show the infection leading to neurodegeneration mediated by multiorgan interconnections and neuroinflammation. Firstly, we highlight three inter-organ communications as possible routes from infection sites to the brain: nose-brain axis, lung-brain axis, and gut-brain axis. Next, we described the biological crosstalk between microglia and astrocytes upon pathogenic infection. Finally, our study indicates how neuroinflammation is a critical player in pathogen-mediated neurodegeneration. Taken together, we envision that antibiotics targeting neuro-pathogens could be a potential therapeutic strategy for neurodegeneration.

Environmental risk factors in multiple sclerosis: bridging Mendelian randomization and observational studies

Multiple sclerosis (MS) is a complex disease with both genetic variants and environmental factors involved in disease susceptibility. The main environmental risk factors associated with MS in observational studies include obesity, vitamin D deficiency, Epstein-Barr virus infection and smoking. As modifying these environmental and lifestyle factors may enable prevention, it is important to pinpoint causal links between these factors and MS. Leveraging genetics through the Mendelian randomization (MR) paradigm is an elegant way to inform prevention strategies in MS. In this review, we summarize MR studies regarding the impact of environmental factors on MS susceptibility, thereby paying attention to quality criteria which will aid readers in interpreting any MR studies. We draw parallels and differences with observational studies and randomized controlled trials and look forward to the challenges that such work presents going forward.

Predicting Multiple Sclerosis: Challenges and Opportunities

Determining effective means of preventing Multiple Sclerosis (MS) relies on testing preventive strategies in trial populations. However, because of the low incidence of MS, demonstrating that a preventive measure has benefit requires either very large trial populations or an enriched population with a higher disease incidence. Risk scores which incorporate genetic and environmental data could be used, in principle, to identify high-risk individuals for enrolment in preventive trials. Here we discuss the concepts of developing predictive scores for identifying individuals at high risk of MS. We discuss the empirical efforts to do so using real cohorts, and some of the challenges-both theoretical and practical-limiting this work. We argue that such scores could offer a means of risk stratification for preventive trial design, but are unlikely to ever constitute a clinically-helpful approach to predicting MS for an individual.

Genetics and functional genomics of multiple sclerosis

Multiple sclerosis (MS) is an inflammatory neurodegenerative disease with genetic predisposition. Over the last decade, genome-wide association studies with increasing sample size led to the discovery of robustly associated genetic variants at an exponential rate. More than 200 genetic loci have been associated with MS susceptibility and almost half of its heritability can be accounted for. However, many challenges and unknowns remain. Definitive studies of disease progression and endophenotypes are yet to be performed, whereas the majority of the identified MS variants are not yet functionally characterized. Despite these shortcomings, the unraveling of MS genetics has opened up a new chapter on our understanding MS causal mechanisms.

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.

Genetically predicted circulating homocysteine, vitamin B12, and folate levels and risk of multiple sclerosis: evidence from a two-sample Mendelian randomization analysis

The association between homocysteine and risk of multiple sclerosis (MS) remains unclear. We implemented a two-sample Mendelian randomization (MR) analysis to comprehensively investigate the causal relationships between circulating homocysteine, vitamin B12 (VitB12), and folate levels and MS with data from large-scale genome-wide association studies. MR results demonstrated an inverse association between genetically predicted higher circulating homocysteine levels (per 1 standard deviation (SD) increase) and risk of MS (OR 0.78, 95% CI 0.64-0.94, p = 0.0106). No significant causal relationships between genetically determined higher VitB12 and folate levels and MS were observed. Further studies are warranted to elucidate the potential mechanisms.

Clinical Features of Late-Onset Multiple Sclerosis: a Systematic Review and Meta-analysis

BACKGROUND

Multiple sclerosis (MS) commonly affects young adults at the ages 20 to 40 years old, but it can onset at each age. Late-onset multiple sclerosis (LOMS) is defined as symptoms initiating after the age of 50. Misdiagnosis and a remarkable gap in diagnosis of LOMS is a challenge of the elderly population so in this article we described the proportion of LOMS and the clinical features and phenotype of the disease in this age group.

METHODS

After registration of the study protocol, an electronic search was performed in 3 databases and for full coverage of the published studies, we also checked the references of each related article. Two independent researchers screened the records in title/abstract and full-text stages and extracted the data using a data extraction table. The risk of bias was assessed using Joanna Briggs Institute checklist and meta-analysis was conducted by CMA 2. Only the studies with 50 years old cut-off and using McDonald or Poser diagnostic criteria were included in the meta-analysis.

RESULTS

After removing duplicated studies, out of 733 results of electronic and hand searching, 31 studies met our inclusion criteria for the systematic review, and 11 of them were included in the quantitative synthesis. With different cut-offs and diagnostic methods 1.1% to 21.3% proportion of LOMS, has been reported in the studies. Meta-analysis reached a 5.01% (95% CI: 3.78% to 6.57%), proportion of LOMS in total MS cases. The female cases were more than males (range between 57.7% to 70.2%) and 64.46% (95% CI: 61.94% to 66.91%) proportion of females has been found in this study. 65.00% (95% CI: 44.71% to 81.02%) proportion of spinal cord involvements and 49.80% (95% CI: 39.28% to 60.24%) proportion of relapsing-remitting multiple sclerosis (RRMS) was also observed in LOMS cases. In 4 of included studies, the progressive form was the predominant phenotype. The most prevalent first disease presentation of LOMS was motor dysfunction (ranges between 100% to 35.4%) followed by sensory problems (ranges between 94% to 5%), visual symptoms (ranges between 22.9% to 5%), and brainstem dysfunction (ranges between 25% to 12.3%). The proportion of positive oligoclonal band (OCB), was varied from 46% to 98% in different studies and positive immunoglobulin G (IgG) index also was seen in 45.04% and 66% of the patients. 2.2% - 12.5% of the LOMS cases had a positive family history.

CONCLUSION

In about 5% of cases, MS can be diagnosed at ages above 50 years old. There is an increasing concern of a more progressive form of MS in LOMS cases. Unlike the adult-onset MS, the first presentation of LOMS is usually motor dysfunction. Understanding the proportion and clinical features of LOMS will help clinicians with the diagnosis of MS in this age group and prevention of wrong management plans and complications in these patients. Although the proportion of females is still more than males in LOMS cases; but there is a trend to increase in male cases with aging.