Smoking and amyotrophic lateral sclerosis: A mendelian randomization study

Clinical and Sociodemographic Factors Related to Amyotrophic Lateral Sclerosis in Spain: A Pilot Study

Background: Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease of unknow etiology. Male sex is a well stablished risk factor, but other factors such as early and adult life expositions show contradictory evidence. Aim: to explore the link of clinical, sociodemographic, and occupational factors with ALS patients in Spain and the impact of these factors in functionality. Methods: A cross-sectional study was conducted with ALS patients and healthy controls. Registered variables were smoking, arterial hypertension, diabetes mellitus type 2, previous cancer to reproductive organs or breast, occupational exposure, and early life exposures. Functionality in ALS patients was compared according to each exposure. Results: The ALS group consisted of 59 participants and the control group of 90 participants. ALS patients showed a significant association with previous cancer (p = 0.011), occupational exposure (p < 0.001), and older siblings (p = 0.029). ALS patients presented significant differences in BMI according to hypertension and older-sibling factors. Moreover, respiratory function was affected in patients with previous cancer (p = 0.031). Conclusions: Occupational exposure and previous cancer to reproductive organs or breast could be linked to ALS patients. In addition, hypertension and previous cancer could affect their BMI and respiratory function. Other factors such as longer smoking periods and exposition to older siblings could also characterize ALS patients.

Lifestyle and medical conditions in relation to ALS risk and progression-an introduction to the Swedish ALSrisc Study

BACKGROUND

This study was an introduction to the Swedish ALSrisc Study and explored the association of lifestyle and medical conditions, with risk and progression of amyotrophic lateral sclerosis (ALS).

METHODS

We included 265 newly diagnosed ALS patients during 2016-2022 in Stockholm and 207 ALS-free siblings and partners of the patients as controls. Information on body mass index (BMI), smoking, and history of head injuries, diabetes mellitus, hypercholesterolemia, and hypertension was obtained through the Euro-MOTOR questionnaire at recruitment. Patients were followed from diagnosis until death, invasive ventilation, or November 30, 2022.

RESULTS

Higher BMI at recruitment was associated with lower risk for ALS (OR 0.89, 95%CI 0.83-0.95), especially among those diagnosed after 65 years. One unit increase in the average BMI during the 3 decades before diagnosis was associated with a lower risk for ALS (OR 0.94, 95%CI 0.89-0.99). Diabetes was associated with lower risk of ALS (OR 0.38, 95%CI 0.16-0.90), while hypercholesterolemia was associated with higher risk of ALS (OR 2.10, 95%CI 1.13-3.90). Higher BMI at diagnosis was associated with lower risk of death (HR 0.91, 95%CI 0.84-0.98), while the highest level of smoking exposure (in pack-years) (HR 1.90, 95%CI 1.20-3.00), hypercholesterolemia (HR 1.84, 95%CI 1.06-3.19), and hypertension (HR 1.76, 95%CI 1.03-3.01) were associated with higher risk of death, following ALS diagnosis.

CONCLUSIONS

Higher BMI and diabetes were associated with lower risk of ALS. Higher BMI was associated with lower risk of death, whereas smoking (especially in high pack-years), hypercholesterolemia, and hypertension were associated with higher risk of death after ALS diagnosis.

Physical Activity, Fitness, and Long-Term Risk of Amyotrophic Lateral Sclerosis: A Prospective Cohort Study

BACKGROUND AND OBJECTIVES

Observational studies have demonstrated an increased amyotrophic lateral sclerosis (ALS) risk among professional athletes in various sports. For moderately increased levels of physical activity and fitness, the results are diverging. Through a cohort study, we aimed to assess the relationship between indicators of physical activity and fitness (self-reported physical activity and resting heart rate) and long-term ALS risk.

METHODS

From a large Norwegian cardiovascular health survey (1985-1999), we collected information on self-reported physical activity in leisure time, resting heart rate, and other cardiovascular risk factors. Patients with ALS were identified through health registries covering the whole population. We fitted Cox proportional hazard models to assess the risk of ALS according to levels of self-reported physical activity in 3 categories (1: sedentary; 2: minimum 4 hours per week of walking or cycling; 3: minimum 4 hours per week of recreational sports or hard training), and resting heart rate modeled both on the continuous scale and as quartiles of distribution.

RESULTS

Out of 373,696 study participants (mean 40.9 [SD 1.1] years at inclusion), 504 (41.2% women) developed ALS during a mean follow-up time of 27.2 (SD 5.0) years. Compared with participants with the lowest level of physical activity, the hazard ratio was 0.71 (95% CI 0.53-0.95) for those with the highest level. There were no clear associations between resting heart rate and ALS in the total sample. In men, the hazard ratio of ALS was 0.71 (95% CI 0.53-0.95) for those reporting moderate levels of physical activity and 0.59 (95% CI 0.42-0.84) for those reporting high levels, compared with those reporting low levels. Men with resting heart rate in the lowest quartile had 32% reduced risk of ALS (hazard ratio 0.68, 95% CI 0.49-0.94) compared with those in the second highest quartile. In women, no association was detected between neither self-reported levels of physical activity nor resting heart rate and ALS risk.

DISCUSSION

Indicators of high levels of physical activity and fitness are associated with a reduced risk of ALS more than 30 years later in men, but not in women.

Dietary factors and risk for amyotrophic lateral sclerosis: A two sample mendelian randomization study

Correlations between dietary factors and amyotrophic lateral sclerosis (ALS) have been found in previous observational studies. However, no further studies have used Mendelian randomization to further explore the causal relationship between dietary factors and ALS. Clarifying these relationships is a crucial part of developing nutritional recommendations for ALS prevention. The exposure and outcome datasets employed in this study were extracted from the IEU Open GWAS project (https://gwas.mrcieu.ac.uk/). The exposure datasets involved in our Mendelian analyses consisted of meat intake (processed meat intake, poultry intake, beef intake, pork intake, non-oily fish intake, and oily fish intake), staple foods intake (bread intake and cereal intake), vegetable intake (cooked vegetable intake, salad/raw vegetable intake), fruit intake (fresh fruit intake and dried fruit intake), and beverage intake (coffee intake and tea intake). The weighted median, MR-Egger, Inverse Variance Weighted, Simple mode and Weighted mode methods were all utilized. And we applied Inverse Variance Weighted method as the main judgement criterion for Mendelian randomization analysis. Heterogeneity and pleiotropy analyses were conducted to confirm the validity of the outcomes. Genetically predicted that oily fish intake (OR: 0.7648; 95% CI: 0.5905-0.9904; P = .0420), coffee intake (OR: 0.7385; 95% CI: 0.5660-0.9637; P = .0256), and fresh fruit intake (OR: 0.6165; 95% CI: 0.4007-0.9487; P = .0278) were causally associated with a decreased risk of ALS. Negative results (P > .05) were received for all other dietary factors. This study found that oily fish intake, coffee intake and fresh fruit intake reduced the risk of developing ALS. Additionally, other factors were not associated with ALS.

From use of omics to systems biology: Identifying therapeutic targets for amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a heterogeneous progressive neurodegenerative disorder with available treatments such as riluzole and edaravone extending survival by an average of 3-6 months. The lack of highly effective, widely available therapies reflects the complexity of ALS. Omics technologies, including genomics, transcriptomic and proteomics have contributed to the identification of biological pathways dysregulated and targeted by therapeutic strategies in preclinical and clinical trials. Integrating clinical, environmental and neuroimaging information with omics data and applying a systems biology approach can further improve our understanding of the disease with the potential to stratify patients and provide more personalised medicine. This chapter will review the omics technologies that contribute to a systems biology approach and how these components have assisted in identifying therapeutic targets. Current strategies, including the use of genetic screening and biosampling in clinical trials, as well as the future application of additional technological advances, will also be discussed.

Premorbid lipid levels and long-term risk of ALS-a population-based cohort study

OBJECTIVE

To assess the temporal relationship between premorbid lipid levels and long-term amyotrophic lateral sclerosis (ALS) risk.

METHODS

From Norwegian cardiovascular health surveys (1974-2003), we collected information on total cholesterol (TC), triglycerides (TG), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), glucose, and other cardiovascular risk factors. ALS incidence and mortality were identified through validated Norwegian health registries. The relation between premorbid lipid levels and ALS risk was assessed by Cox regression models.

RESULTS

Out of 640,066 study participants (51.5% females), 974 individuals (43.5% females) developed ALS. Mean follow-up time was 23.7 (SD 7.1) years among ALS cases. One mmol/l increase in LDL-C was associated with 6% increase in risk for ALS (hazard ratio 1.06 [95% CI: 1.01-1.09]). Higher levels of TC and TG were also associated with increased ALS risk, but only within the last 6-7 years prior to ALS diagnosis or death. No association between HDL-C and ALS risk was found. Adjusting for body mass index, birth cohort, smoking, and physical activity did not alter the results.

CONCLUSIONS

Higher levels of LDL-C are associated with increased ALS risk over 40 years later, compatible with a causal relationship. The temporal relationship between TG, TC, and ALS risk suggests that increased levels of these lipid biomarkers represent consequences of ALS.

Tuberculin responses after BCG vaccination predict amyotrophic lateral sclerosis risk

Background

T cell infiltration around dying motor neurons is a hallmark of amyotrophic lateral sclerosis (ALS). It is not known if this immune response represents a cause or a consequence of the disease. We aimed to establish whether individual variation in regulation of a T cell driven immune response is associated with long-term ALS risk.

Methods

Tuberculin skin test (TST) following BCG vaccination represents a standardized measure of a secondary T cell driven immune response. During a Norwegian tuberculosis screening program (1963-1975) Norwegian citizens born from 1910 to 1955 underwent TST. In those previously BCG vaccinated (median 7 years prior to TST), we related tuberculin skin tests to later ALS disease identified through validated Norwegian health registers. We fitted Cox proportional hazard models to investigate the association between tuberculin reactivity and ALS risk.

Results

Among 324,629 participants (52 % women) with median age 22 (IQR 10) years at tuberculosis screening, 496 (50 % women) later developed ALS. Hazard ratio for ALS was 0.74 (95% CI 0.57-0.95) for those who remained TST negative compared to those who mounted a positive TST. The association was strongest when time between BCG immunization and TST was short. The associations observed persisted for more than four decades after TST measurement.

Conclusions

Negative TST responses after BCG vaccination is associated with decreased long-term risk for ALS development, supporting a primary role for adaptive immunity in ALS development.

Neutrophils Are Associated with Higher Risk of Incident Amyotrophic Lateral Sclerosis in a BMI- and Age-Dependent Manner

OBJECTIVE

Peripheral immune markers have been associated with the progression and prognosis of amyotrophic lateral sclerosis (ALS). However, whether dysregulation of peripheral immunity is a risk factor for ALS or a consequence of motor neuron degeneration has not yet been clarified. We aimed to identify longitudinal associations between prediagnostic peripheral immunity and the risk of incident ALS.

METHODS

A total of 345,000 individuals from the UK Biobank between 2006 and 2010 were included at the baseline. The counts of peripheral immune markers (neutrophils, lymphocytes, monocytes, platelets, and CRP) and its derived metrics (neutrophil-to-lymphocyte ratio [NLR], platelet-to-lymphocyte ratio [PLR], lymphocyte-to-monocyte ratio [LMR], and systemic immune-inflammation index [SII]) were analyzed in relation to the following incident ALS by Cox proportional hazard models. Subgroup and interaction analyses were performed to explore the covariates of these relationships further.

RESULTS

After adjusting for all covariates, the multivariate analysis showed that high neutrophil counts and their derived metrics (NLR and SII) were associated with an increased risk of ALS incidence (per SD increment hazard ratio [HR] = 1.15, 95% confidence interval [CI] = 1.02-1.29 for neutrophils; HR = 1.15, 95% CI = 1.03-1.28 for NLR; and HR = 1.17, 95% CI = 1.05-1.30 for SII). Subgroup and interaction analyses revealed that body mass index (BMI) and age had specific effects on this association. In participants with BMI ≥ 25 or age < 65 years, higher neutrophil counts, and their metrics increased the risk of incident ALS; however, in participants with BMI < 25 or age ≥ 65 years, neutrophils had no effect on incident ALS.

INTERPRETATION

Our study provides evidence that increased neutrophil levels and neutrophil-derived metrics (NLR and SII) are associated with an increased risk of developing ALS. ANN NEUROL 2023;94:942-954.

Evaluating the causal effect of tobacco smoking on white matter brain aging: a two-sample Mendelian randomization analysis in UK Biobank

BACKGROUND AND AIMS

Tobacco smoking is a risk factor for impaired brain function, but its causal effect on white matter brain aging remains unclear. This study aimed to measure the causal effect of tobacco smoking on white matter brain aging.

DESIGN

Mendelian randomization (MR) analysis using two non-overlapping data sets (with and without neuroimaging data) from UK Biobank (UKB). The group exposed to smoking and control group consisted of current smokers and never smokers, respectively. Our main method was generalized weighted linear regression with other methods also included as sensitivity analysis.

SETTING

United Kingdom.

PARTICIPANTS

The study cohort included 23 624 subjects [10 665 males and 12 959 females with a mean age of 54.18 years, 95% confidence interval (CI) = 54.08, 54.28].

MEASUREMENTS

Genetic variants were selected as instrumental variables under the MR analysis assumptions: (1) associated with the exposure; (2) influenced outcome only via exposure; and (3) not associated with confounders. The exposure smoking status (current versus never smokers) was measured by questionnaires at the initial visit (2006-10). The other exposure, cigarettes per day (CPD), measured the average number of cigarettes smoked per day for current tobacco users over the life-time. The outcome was the 'brain age gap' (BAG), the difference between predicted brain age and chronological age, computed by training machine learning model on a non-overlapping set of never smokers.

FINDINGS

The estimated BAG had a mean of 0.10 (95% CI = 0.06, 0.14) years. The MR analysis showed evidence of positive causal effect of smoking behaviors on BAG: the effect of smoking is 0.21 (in years, 95% CI = 6.5 × 10-3 , 0.41; P-value = 0.04), and the effect of CPD is 0.16 year/cigarette (UKB: 95% CI = 0.06, 0.26; P-value = 1.3 × 10-3 ; GSCAN: 95% CI = 0.02, 0.31; P-value = 0.03). The sensitivity analyses showed consistent results.

CONCLUSIONS

There appears to be a significant causal effect of smoking on the brain age gap, which suggests that smoking prevention can be an effective intervention for accelerated brain aging and the age-related decline in cognitive function.

A review of Mendelian randomization in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis is a relatively common and rapidly progressive neurodegenerative disease that, in the majority of cases, is thought to be determined by a complex gene-environment interaction. Exponential growth in the number of performed genome-wide association studies combined with the advent of Mendelian randomization is opening significant new opportunities to identify environmental exposures that increase or decrease the risk of amyotrophic lateral sclerosis. Each of these discoveries has the potential to shape new therapeutic interventions. However, to do so, rigorous methodological standards must be applied in the performance of Mendelian randomization. We have reviewed Mendelian randomization studies performed in amyotrophic lateral sclerosis to date. We identified 20 Mendelian randomization studies, including evaluation of physical exercise, adiposity, cognitive performance, immune function, blood lipids, sleep behaviours, educational attainment, alcohol consumption, smoking and type 2 diabetes mellitus. We have evaluated each study using gold standard methodology supported by the Mendelian randomization literature and the STROBE-Mendelian randomization checklist. Where discrepancies exist between Mendelian randomization studies, we suggest the underlying reasons. A number of studies conclude that there is a causal link between blood lipids and risk of amyotrophic lateral sclerosis; replication across different datasets and even different populations adds confidence. For other putative risk factors, such as smoking and immune function, Mendelian randomization studies have provided cause for doubt. We highlight the use of positive control analyses in choosing exposure single nucleotide polymorphisms (SNPs) to make up the Mendelian randomization instrument, use of SNP clumping to avoid false positive results due to SNPs in linkage and the importance of multiple testing correction. We discuss the implications of survival bias for study of late age of onset diseases such as amyotrophic lateral sclerosis and make recommendations to mitigate this potentially important confounder. For Mendelian randomization to be useful to the amyotrophic lateral sclerosis field, high methodological standards must be applied to ensure reproducibility. Mendelian randomization is already an impactful tool, but poor-quality studies will lead to incorrect interpretations by a field that includes non-statisticians, wasted resources and missed opportunities.

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.

1,2-Dehydropyrrolizidine Alkaloids: Their Potential as a Dietary Cause of Sporadic Motor Neuron Diseases

Sporadic motor neuron diseases (MNDs), such as amyotrophic lateral sclerosis (ALS), can be caused by spontaneous genetic mutations. However, many sporadic cases of ALS and other debilitating neurodegenerative diseases (NDDs) are believed to be caused by environmental factors, subject to considerable debate and requiring intensive research. A common pathology associated with MND development involves progressive mitochondrial dysfunction and oxidative stress in motor neurons and glial cells of the central nervous system (CNS), leading to apoptosis. Consequent degeneration of skeletal and respiratory muscle cells can lead to death from respiratory failure. A significant number of MND cases present with cancers and liver and lung pathology. This Perspective explores the possibility that MNDs could be caused by intermittent, low-level dietary exposure to 1,2-dehydropyrrolizidine alkaloids (1,2-dehydroPAs) that are increasingly recognized as contaminants of many foods consumed throughout the world. Nontoxic, per se, 1,2-dehydroPAs are metabolized, by particular cytochrome P450 (CYP450) isoforms, to 6,7-dihydropyrrolizines that react with nucleophilic groups (-NH, -SH, -OH) on DNA, proteins, and other vital biochemicals, such as glutathione. Many factors, including aging, gender, smoking, and alcohol consumption, influence CYP450 isoform activity in a range of tissues, including glial cells and neurons of the CNS. Activation of 1,2-dehydroPAs in CNS cells can be expected to cause gene mutations and oxidative stress, potentially leading to the development of MNDs and other NDDs. While relatively high dietary exposure to 1,2-dehydroPAs causes hepatic sinusoidal obstruction syndrome, pulmonary venoocclusive disease, neurotoxicity, and diverse cancers, this Perspective suggests that, at current intermittent, low levels of dietary exposure, neurotoxicity could become the primary pathology that develops over time in susceptible individuals, along with a tendency for some of them to also display liver and lung pathology and diverse cancers co-occurring with some MND/NDD cases. Targeted research is recommended to investigate this proposal.

Higher blood high density lipoprotein and apolipoprotein A1 levels are associated with reduced risk of developing amyotrophic lateral sclerosis

BACKGROUND

Premorbid body mass index, physical activity, diabetes and cardiovascular disease have been associated with an altered risk of developing amyotrophic lateral sclerosis (ALS). There is evidence of shared genetic risk between ALS and lipid metabolism. A very large prospective longitudinal population cohort permits the study of a range of metabolic parameters and the risk of subsequent diagnosis of ALS.

METHODS

The risk of subsequent ALS diagnosis in those enrolled prospectively to the UK Biobank (n=502 409) was examined in relation to baseline levels of blood high and low density lipoprotein (HDL, LDL), total cholesterol, total cholesterol:HDL ratio, apolipoproteins A1 and B (apoA1, apoB), triglycerides, glycated haemoglobin A1c (HbA1c) and creatinine, plus self-reported exercise and body mass index.

RESULTS

Controlling for age and sex, higher HDL (HR 0.84, 95% CI 0.73 to 0.96, p=0.010) and apoA1 (HR 0.83, 95% CI 0.72 to 0.94, p=0.005) were associated with a reduced risk of ALS. Higher total cholesterol:HDL was associated with an increased risk of ALS (HR 1.17, 95% CI 1.05 to 1.31, p=0.006). In models incorporating multiple metabolic markers, higher LDL or apoB was associated with an increased risk of ALS, in addition to a lower risk with higher HDL or apoA. Coronary artery disease, cerebrovascular disease and increasing age were also associated with an increased risk of ALS.

CONCLUSIONS

The association of HDL, apoA1 and LDL levels with risk of ALS contributes to an increasing body of evidence that the premorbid metabolic landscape may play a role in pathogenesis. Understanding the molecular basis for these changes will inform presymptomatic biomarker development and therapeutic targeting.

Unraveling the complex interplay between genes, environment, and climate in ALS

Various genetic and environmental risk factors have been implicated in the pathogenesis of amyotrophic lateral sclerosis (ALS). Despite this, the cause of most ALS cases remains obscure. In this review, we describe the current evidence implicating genetic and environmental factors in motor neuron degeneration. While the risk exerted by many environmental factors may appear small, their effect could be magnified by the presence of a genetic predisposition. We postulate that gene-environment interactions account for at least a portion of the unknown etiology in ALS. Climate underlies multiple environmental factors, some of which have been implied in ALS etiology, and the impact of global temperature increase on the gene-environment interactions should be carefully monitored. We describe the main concepts underlying such interactions. Although a lack of large cohorts with detailed genetic and environmental information hampers the search for gene-environment interactions, newer algorithms and machine learning approaches offer an opportunity to break this stalemate. Understanding how genetic and environmental factors interact to cause ALS may ultimately pave the way towards precision medicine becoming an integral part of ALS care.

Pre-Morbid Risk Factors for Amyotrophic Lateral Sclerosis: Prospective Cohort Study

AIM

In the absence of effective treatments for amyotrophic lateral sclerosis (ALS), a neurodegenerative disorder with high case fatality, there is a clear need to identify its primary risk factors.

METHODS

UK Biobank is a prospective cohort study in which baseline data were captured between 2006 and 2010 in 502,649 participants aged 37 to 73 years. Follow-up for ALS hospitalisations and death was made via national registries.

RESULTS

Eleven years of event surveillance gave rise to 301 hospitalisations and 279 deaths due to ALS. After adjustment for selected confounding factors, being older (hazard ratio per 10 year increase; 95% confidence interval: 1.92; 1.58, 2.33) and male (1.37; 1.00, 1.87) were associated with elevated rates of hospitalisation for ALS. Similar effects were apparent when death ascribed to the disorder was the outcome of interest. Of the remaining 23 social, biological, and behavioural risk indices, however, there was only a suggestion that taller people experienced an increased risk of hospitalisation (per SD increase: 1.31; 1.09, 1.59).

CONCLUSION

In the present, large-scale study, other than well known associations, we did not find convincing evidence of links with ALS for other risk indices.

Gut microbiome and amyotrophic lateral sclerosis: A systematic review of current evidence

Amyotrophic lateral sclerosis (ALS), characterized by a loss of motor neurons in the brain and spinal cord, is a relatively rare but currently incurable neurodegenerative disease. The global incidence of ALS is estimated as 1.75 per 100,000 person-years and the global prevalence is estimated as 4.1-8.4 per 100,000 individuals. Contributions from outside the central nervous system to the etiology of ALS have been increasingly recognized. Gut microbiome is one of the most quickly growing fields of research for ALS. In this article, we performed a comprehensive review of the results from existing animal and human studies, to provide an up-to-date summary of the current research on gut microbiome and ALS. In brief, we found relatively consistent results from animal studies, suggesting an altered gut microbiome composition in experimental ALS. Publication bias might however be a concern. Findings from human studies are largely inconclusive. A few animal and human studies demonstrated the usefulness of intervention with microbial-derived metabolites in modulating the disease progression of ALS. We discussed potential methodological concerns in these studies, including study design, statistical power, handling process of biospecimens and sequencing data, as well as statistical methods and interpretation of results. Finally, we made a few proposals for continued microbiome research in ALS, with the aim to provide valid, reproducible, and translatable findings.

Oxidative Stress as a Therapeutic Target in Amyotrophic Lateral Sclerosis: Opportunities and Limitations

Amyotrophic lateral sclerosis (ALS), also known as motor neuron disease (MND) and Lou Gehrig’s disease, is characterized by a loss of the lower motor neurons in the spinal cord and the upper motor neurons in the cerebral cortex. Due to the complex and multifactorial nature of the various risk factors and mechanisms that are related to motor neuronal degeneration, the pathological mechanisms of ALS are not fully understood. Oxidative stress is one of the known causes of ALS pathogenesis. This has been observed in patients as well as in cellular and animal models, and is known to induce mitochondrial dysfunction and the loss of motor neurons. Numerous therapeutic agents have been developed to inhibit oxidative stress and neuroinflammation. In this review, we describe the role of oxidative stress in ALS pathogenesis, and discuss several anti-inflammatory and anti-oxidative agents as potential therapeutics for ALS. Although oxidative stress and antioxidant fields are meaningful approaches to delay disease progression and prolong the survival in ALS, it is necessary to investigate various animal models or humans with different subtypes of sporadic and familial ALS.

A Novel Method for Mendelian Randomization Analyses With Pleiotropy and Linkage Disequilibrium in Genetic Variants From Individual Data

Mendelian randomization makes use of genetic variants as instrumental variables to eliminate the influence induced by unknown confounders on causal estimation in epidemiology studies. However, with the soaring genetic variants identified in genome-wide association studies, the pleiotropy, and linkage disequilibrium in genetic variants are unavoidable and may produce severe bias in causal inference. In this study, by modeling the pleiotropic effect as a normally distributed random effect, we propose a novel mixed-effects regression model-based method PLDMR, pleiotropy and linkage disequilibrium adaptive Mendelian randomization, which takes linkage disequilibrium into account and also corrects for the pleiotropic effect in causal effect estimation and statistical inference. We conduct voluminous simulation studies to evaluate the performance of the proposed and existing methods. Simulation results illustrate the validity and advantage of the novel method, especially in the case of linkage disequilibrium and directional pleiotropic effects, compared with other methods. In addition, by applying this novel method to the data on Atherosclerosis Risk in Communications Study, we conclude that body mass index has a significant causal effect on and thus might be a potential risk factor of systolic blood pressure. The novel method is implemented in R and the corresponding R code is provided for free download.

Polygenic associations and causal inferences between serum immunoglobulins and amyotrophic lateral sclerosis

BACKGROUND

Due to the limitations like reverse causation and residual confounding commonly seen in the observational studies, the relationship between serum immunoglobulins and amyotrophic lateral sclerosis (ALS) remains unclear.

METHODS

Summary statistics from large-scale genome-wide association studies (GWAS) among European ancestry populations (~15,000 individuals for serum immunoglobulins, and more than 36,000 individuals for ALS) were accessed and used in the discovery and replication phase, respectively. Polygenic risk score analysis was performed to test the polygenic association, and Mendelian randomization analysis was used to infer the causality.

RESULTS

An inverse polygenic association was discovered between IgA and ALS, as well as between IgM and ALS. Such associations were however not replicated using a larger GWAS of ALS, and no causal association was observed for either IgA-ALS or IgM-ALS. For IgG and ALS, a positive polygenic association was both discovered [odds ratio (OR) = 1.18, 95% confidence interval (CI): 1.12-1.25, P = 5.9x10^-7] and replicated (OR = 1.13, 95% CI: 1.06-1.20, P = 0.001). A causal association between IgG and ALS was suggested in the discovery analysis (OR = 1.06, 95 %CI: 1.02-1.10, P = 0.009), but it was not statistically significant in the replication analysis (OR = 1.07, 95 %CI: 0.90-1.24, P = 0.420).

CONCLUSION

This study suggests a positive polygenic association between serum IgG and ALS.

Physical exercise is a risk factor for amyotrophic lateral sclerosis: Convergent evidence from Mendelian randomisation, transcriptomics and risk genotypes

Background

Amyotrophic lateral sclerosis (ALS) is a universally fatal neurodegenerative disease. ALS is determined by gene-environment interactions and improved understanding of these interactions may lead to effective personalised medicine. The role of physical exercise in the development of ALS is currently controversial.

Methods

First, we dissected the exercise-ALS relationship in a series of two-sample Mendelian randomisation (MR) experiments. Next we tested for enrichment of ALS genetic risk within exercise-associated transcriptome changes. Finally, we applied a validated physical activity questionnaire in a small cohort of genetically selected ALS patients.

Findings

We present MR evidence supporting a causal relationship between genetic liability to frequent and strenuous leisure-time exercise and ALS using a liberal instrument (multiplicative random effects IVW, p=0.01). Transcriptomic analysis revealed that genes with altered expression in response to acute exercise are enriched with known ALS risk genes (permutation test, p=0.013) including C9ORF72, and with ALS-associated rare variants of uncertain significance. Questionnaire evidence revealed that age of onset is inversely proportional to historical physical activity for C9ORF72-ALS (Cox proportional hazards model, Wald test p=0.007, likelihood ratio test p=0.01, concordance=74%) but not for non-C9ORF72-ALS. Variability in average physical activity was lower in C9ORF72-ALS compared to both non-C9ORF72-ALS (F-test, p=0.002) and neurologically normal controls (F-test, p=0.049) which is consistent with a homogeneous effect of physical activity in all C9ORF72-ALS patients.

Interpretation

Our MR approach suggests a positive causal relationship between ALS and physical exercise. Exercise is likely to cause motor neuron injury only in patients with a risk-genotype. Consistent with this we have shown that ALS risk genes are activated in response to exercise. In particular, we propose that G4C2-repeat expansion of C9ORF72 predisposes to exercise-induced ALS.

Funding

We acknowledge support from the Wellcome Trust (JCK, 216596/Z/19/Z), NIHR (PJS, NF-SI-0617-10077; IS-BRC-1215-20017) and NIH (MPS, CEGS 5P50HG00773504, 1P50HL083800, 1R01HL101388, 1R01-HL122939, S10OD025212, P30DK116074, and UM1HG009442).

Associations between lifestyle and amyotrophic lateral sclerosis stratified by C9orf72 genotype: a longitudinal, population-based, case-control study

BACKGROUND

Amyotrophic lateral sclerosis (ALS) is considered to be caused by both genetic and environmental factors. The causal cascade is, however, not known. We aimed to assess lifestyle during the presymptomatic phase of ALS, stratified by C9orf72 mutation, and examine evidence supporting causality of lifestyle factors.

METHODS

This study was a longitudinal, population-based, case-control study that used data from the Prospective ALS study the Netherlands. We included patients with a C9orf72 mutation (C9+ group), patients without a C9orf72 mutation (C9- group), and controls. Patients fulfilled the revised El Escorial criteria and were recruited through neurologists and rehabilitation physicians in the Netherlands as well as the Dutch Neuromuscular Patient Association and ALS Centrum website. 1322 population-based controls, matched for age and sex, were enrolled via the patients' general practitioners. Blood relatives or spouses of patients were not eligible as controls. We studied the relationship between ALS risk and smoking, alcohol, physical activity, body-mass index (BMI), and energy intake by the use of structured questionnaires. Smoking, physical activity, and BMI were longitudinally assessed up to 50 years before onset (defined as the period before onset of muscle weakness or bulbar symptoms for cases, or age at completing the questionnaire for controls). We calculated posterior probabilities (P(θ|x)) for causal effects of smoking, alcohol, and BMI, using Bayesian instrumental variable analyses.

FINDINGS

Between Jan 1, 2006 and Jan 27, 2016, we included 143 patients in the C9+ group, 1322 patients in the C9- group, and 1322 controls. Compared with controls, cigarette pack-years (C9+ group mean difference from control 3·15, 95% CI 0·36 to 5·93, p=0·027; C9- group 3·20, 2·02 to 4·39, p<0·0001) and daily energy intake at symptom onset (C9+ group 712 kJ, 95% CI 212 to 1213, p=0·0053; C9- group 497, 295 to 700, p<0·0001) were higher in the C9+ and C9- groups, whereas current BMI (C9+ group -2·01 kg/m², 95% CI -2·73 to -1·29, p<0·0001; C9- group -1·35, -1·64 to -1·06, p<0·0001) and lifetime alcohol consumption (C9+ group -5388 units, 95% CI -9113 to -1663, p=0·0046; C9- group -2185, -3748 to -622, p=0·0062) were lower in the C9+ and C9- groups. Median BMI during the presymptomatic phase for the C9+ group was lower (-0·69 kg/m², 95% CI -1·24 to -0·13, p=0·015) and physical activity was similar (-348 metabolic equivalent of task [MET], 95% CI -966 to 270, p=0·27) to controls, whereas both the median BMI during the presymptomatic phase (0·27 kg/m², 95% CI 0·04 to 0·50, p=0·022) and physical activity (585 MET, 291 to 878, p=0·0001) were higher in the C9- group than controls. Longitudinal analyses showed more cigarette pack-years in the C9- (starting 47 years pre-onset) and C9+ (starting 24 years pre-onset) groups, and higher physical activity over time in the C9- group (starting >30 years pre-onset). BMI of the C9+ group increased more slowly and was significantly lower (starting at 36 years pre-onset) than in controls, whereas the BMI of the C9- group was higher than controls (23-49 years pre-onset, becoming lower 10 years pre-onset). Instrumental variable analyses supported causal effects of alcohol consumption (P(θ|x)=0·9347) and smoking (P(θ|x)=0·9859) on ALS in the C9- group. We found evidence supporting a causal effect of increased BMI at younger age (mean 33·8 years, SD 11·7) in the C9- group (P[θ|x]=0·9272), but not at older ages.

INTERPRETATION

Lifestyle during the presymptomatic phase differs between patients with ALS and controls decades before onset, depends on C9- status, and is probably part of the presymptomatic causal cascade. Identification of modifiable disease-causing lifestyle factors offers opportunities to lower risk of developing neurodegenerative disease.

FUNDING

Netherlands ALS Foundation.

Application of a bioinformatic pipeline to RNA-seq data identifies novel viruslike sequence in human blood

Numerous reports have suggested that infectious agents could play a role in neurodegenerative diseases, but specific etiological agents have not been convincingly demonstrated. To search for candidate agents in an unbiased fashion, we have developed a bioinformatic pipeline that identifies microbial sequences in mammalian RNA-seq data, including sequences with no significant nucleotide similarity hits in GenBank. Effectiveness of the pipeline was tested using publicly available RNA-seq data and in a reconstruction experiment using synthetic data. We then applied this pipeline to a novel RNA-seq dataset generated from a cohort of 120 samples from amyotrophic lateral sclerosis patients and controls, and identified sequences corresponding to known bacteria and viruses, as well as novel virus-like sequences. The presence of these novel virus-like sequences, which were identified in subsets of both patients and controls, were confirmed by quantitative RT-PCR. We believe this pipeline will be a useful tool for the identification of potential etiological agents in the many RNA-seq datasets currently being generated.

Pathophysiological Correlation between Cigarette Smoking and Amyotrophic Lateral Sclerosis

Cigarette smoke (CS) has been consistently demonstrated to be an environmental risk factor for amyotrophic lateral sclerosis (ALS), although the molecular pathogenic mechanisms involved are yet to be elucidated. Here, we propose different mechanisms by which CS exposure can cause sporadic ALS pathogenesis. Oxidative stress and neuroinflammation are widely implicated in ALS pathogenesis, with blood–spinal cord barrier disruption also recognised to be involved in the disease process. In addition, immunometabolic, epigenetic and microbiome alterations have been implicated in ALS recently. Identification of the underlying pathophysiological mechanisms that underpin CS-associated ALS will drive future research to be conducted into new targets for treatment.

No association of GSTP1 rs1695 polymorphism with amyotrophic lateral sclerosis: A case-control study in the Brazilian population

Amyotrophic Lateral Sclerosis (ALS) is a rare neurodegenerative disease that affects motor neurons and promotes progressive muscle atrophy. It has a multifactorial etiology, where environmental conditions playing a remarkable role through the increase of oxidative stress. Genetic polymorphisms in cell detoxification genes, such as Glutathione S-Transferase Pi 1 (GSTP1) can contribute to excessive oxidative stress, and therefore may be a risk factor to ALS. Thus, this study aimed to investigate the role of the GSTP1 rs1695 polymorphism in ALS susceptibility in different genetic inheritance models and evaluate the association of the genotypes with risk factors, clinical and demographic characteristics of ALS patients from the Brazilian central population. This case-control study was conducted with 101 patients with ALS and 101 healthy controls. GSTP1 rs1695 polymorphism genotyping was performed with Polymerase Chain Reaction-Restriction Fragment Length Polymorphism (PCR-RFLP). The statistical analysis was carried out using the SPSS statistical package and SNPStats software. Analysis of genetic inheritance models was performed by logistic regression, which was used to determine the Odds Ratio. The results of this first study in the Brazilian population demonstrated that there was no risk association between the development of ALS and the GSTP1 rs1695 polymorphism in any genetic inheritance model (codominant, dominant, recessive, overdominant, and logarithmic); and that the polymorphic variants were not associated with the clinical and demographic characteristics of ALS patients. No association of the GSTP1 rs1695 polymorphism and ALS development in the Brazilian central population was found. These findings may be justified by the multifactorial character of the disease.

Serum Creatinine Protects Against Amyotrophic Lateral Sclerosis: a Mendelian Randomization Study

Association between serum creatinine (sCr) and amyotrophic lateral sclerosis (ALS) has been reported in previous observational studies, but results are at risk of confounding bias and reverse causation. Therefore, whether such association is casual remains unclear. Herein, we performed a two-sample Mendelian randomization study to evaluate the causal relationship between sCr and ALS in both European and East Asian populations. Our analysis was conducted using summary statistics from genome-wide association studies with 358,072 individuals for sCr and 80,610 individuals for ALS in European population, and 142,097 individuals for sCr and 4,084 individuals for ALS in East Asian population. The inverse-variance weighted method was used to estimate the casual-effect of sCr on ALS in both populations, and other MR methods were also performed as sensitivity analyses. We found evidence that genetically predicted sCr was inversely associated with risk of ALS (OR, 0.92; 95% CI, 0.85-0.99; P = 0.028) in European population. However, there was no strong evidence for a causal relationship between sCr and ALS in East Asian population (OR, 0.92; 95% CI, 0.84-1.01; P = 0.084). This study provides evidence that sCr protects against ALS in European population but not in East Asian population.

Diagnostics of Amyotrophic Lateral Sclerosis: Up to Date

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease characterized by gradual loss of upper and lower motor neurons and their pathways, usually without affecting the extraocular and sphincter muscles. The cause of the disease is not yet known. It is a chain of subsequent events, ending in programmed cell death in selective neuronal subpopulations. The prognosis for survival is rather short with a median of 2 to 4 years. Survival may be prolonged based on prompt diagnosis, ALS subtype and proper management with supportive treatment (tracheostomy, gastrostomy, etc.). According to the clinical picture, the typical form of ALS with upper and lower motoneuron involvement and progressive bulbar paralysis with bulbar muscle involvement is observed. The ALS form with progressive muscle atrophy, where only the lower motoneuron is affected, and primary lateral sclerosis with only upper motoneuron damage are rare. Familiar forms of ALS (FALS) associated with specific genes (the most common is C9orf72) have been discovered. FALS is usually associated with dementia (frontotemporal lobar dementia, FTLD), behavioral disorders, cognitive dysfunction and impairment of executive functions. The diagnosis of ALS is determined by excluding other conditions and utilizing clinical examinations, laboratory and genetic tests and nerve conduction/needle electromyography studies (EMG). Needle EMG records abnormal activities at rest and looks for neurogenic patterns during muscle contraction. Motor evoked potentials after transcranial magnetic stimulation remain the test of choice to identify impairment of upper motor neurons. New biochemical, neurophysiological and morphological biomarkers are extensively studied as early diagnostic and prognostic factors and have implications for clinical trials, research and drug development.

Relationship between smoking and ALS: Mendelian randomisation interrogation of causality

OBJECTIVE

Smoking has been widely studied as a susceptibility factor for amyotrophic lateral sclerosis (ALS), but results are conflicting and at risk of confounding bias. We used the results of recently published large genome-wide association studies and Mendelian randomisation methods to reduce confounding to assess the relationship between smoking and ALS.

METHODS

Two genome-wide association studies investigating lifetime smoking (n=463 003) and ever smoking (n=1 232 091) were identified and used to define instrumental variables for smoking. A genome-wide association study of ALS (20 806 cases; 59 804 controls) was used as the outcome for inverse variance weighted Mendelian randomisation, and four other Mendelian randomisation methods, to test whether smoking is causal for ALS. Analyses were bidirectional to assess reverse causality.

RESULTS

There was no strong evidence for a causal or reverse causal relationship between smoking and ALS. The results of Mendelian randomisation using the inverse variance weighted method were: lifetime smoking OR 0.94 (95% CI 0.74 to 1.19), p value 0.59; ever smoking OR 1.10 (95% CI 1 to 1.23), p value 0.05.

CONCLUSIONS

Using multiple methods, large sample sizes and sensitivity analyses, we find no evidence with Mendelian randomisation techniques that smoking causes ALS. Other smoking phenotypes, such as current smoking, may be suitable for future Mendelian randomisation studies.

Association of Cigarette Smoking With Cerebrospinal Fluid Biomarkers of Neurodegeneration, Neuroinflammation, and Oxidation

IMPORTANCE

Cigarette smoking has been associated with risk of neurodegenerative disorders, such as Alzheimer disease. The association between smoking and biomarkers of changes in human cerebrospinal fluid (CSF) is not fully understood.

OBJECTIVE

To investigate the association of cigarette smoking with CSF biomarkers of neurodegeneration, neuroinflammation, oxidation, and neuroprotection.

DESIGN, SETTING, AND PARTICIPANTS

In this case-control study of 191 adult men in China, biomarkers in the CSF of participants with and without significant cigarette exposure were examined. Participants who did not smoke and had no history of substance use disorder or dependence were assigned to the nonsmoking group. The active smoking group included participants who consumed at least 10 cigarettes per day for 1 year. Five-milliliter samples of CSF were obtained from routine lumbar puncture conducted before anterior cruciate ligament reconstruction surgery. Data collection took place from September 2014 to January 2016, and analysis took place from January to February 2016.

EXPOSURES

Cigarette smoking.

MAIN OUTCOMES AND MEASURES

CSF levels of β-amyloid 42 (Aβ42), which has diagnostic specificity for Alzheimer disease, tumor necrosis factor alpha (TNFα), brain-derived neurotrophic factor (BDNF), total superoxide dismutase (SOD), and nitric oxide synthase (NOS) were measured. Sociodemographic data and history of smoking were obtained.

RESULTS

Of 191 participants, 87 (45.5%) were included in the active smoking group and 104 (54.4%) in the nonsmoking group. Compared with the active smoking group, the nonsmoking group was younger (mean [SD] age, 34.4 [10.5] years vs 29.6 [9.5] years; P = .01), had more education (mean [SD] duration of education, 11.9 [3.1] years vs 13.2 [2.6] years; P = .001), and had lower body mass index (mean [SD], 25.9 [3.6] vs 24.9 [4.0]; P = .005). Comparing the nonsmoking group with the smoking group, mean (SD) CSF levels of Aβ42 (38.0 [25.9] pg/mL vs 52.8 [16.5] pg/mL; P < .001) and TNFα (23.0 [2.5] pg/mL vs 28.0 [2.0] pg/mL; P < .001) were significantly lower, while BDNF (23.1 [3.9] pg/mL vs 13.8 [2.7] pg/mL; P < .001), total SOD (15.7 [2.6] U/L vs 13.9 [2.4] U/L; P < .001), total NOS (28.3 [7.2] U/L vs 14.7 [5.6] U/L; P < .001), inducible NOS (16.0 [5.4] U/L vs 10.3 [2.7] U/L; P < .001), and constitutive NOS (12.4 [6.9] U/mL vs 4.4 [3.9] U/mL) were higher. In addition, in participants in the smoking group who were aged 40 years or older, total SOD levels were negatively correlated with Aβ42 levels (r = -0.57; P = .02). In those who smoked at least 20 cigarettes per day, TNFα levels were positively correlated with Aβ42 levels (r = 0.51; P = .006). The association of TNFα with Aβ42 production was stronger than that of total SOD with Aβ42 production (z = -4.38; P < .001).

CONCLUSIONS AND RELEVANCE

This case-control study found that cigarette smoking was associated with at-risk biomarkers for Alzheimer disease, as indicated by higher Aβ42 levels, excessive oxidative stress, neuroinflammation, and impaired neuroprotection found in the CSF of participants in the active smoking group.

Diabetes mellitus is associated with a lower risk of amyotrophic lateral sclerosis: A systematic review and meta-analysis

BACKGROUND/AIMS

Previous studies have suggested that diabetes mellitus (DM) could be a protective factor against amyotrophic lateral sclerosis (ALS) although the results are inconsistent. This study aimed to comprehensively investigate this relationship by identifying all available studies and summarizing their results.

METHODS

A systematic review was conducted in MEDLINE and EMBASE database from inception to January 1st, 2020 to identify cohort studies and case-control studies that investigated the risk of development of ALS among patients with DM versus individuals without DM. Point estimates and standard errors from eligible studies were pooled together using the generic inverse variance method, as described by DerSimonian and Laird. Visualization of the funnel plot was used to assess for the presence of publication bias.

RESULTS

A total of 1683 articles were identified by the search strategy. After two rounds of review, three cohort studies and eight case-control studies fulfilled the inclusion criteria and were included in the meta-analysis. The risk of developing ALS was significantly lower among patients with DM than individuals without DM with the pooled relative risk of 0.68 (95 % CI, 0.55 - 0.84; I² 81 %). The funnel plot was relatively symmetric and was not suggestive of the presence of publication bias.

CONCLUSION

A significantly decreased risk of ALS among patients with DM was observed in this meta-analysis.

Immunity in amyotrophic lateral sclerosis: blurred lines between excessive inflammation and inefficient immune responses

Despite wide genetic, environmental and clinical heterogeneity in amyotrophic lateral sclerosis, a rapidly fatal neurodegenerative disease targeting motoneurons, neuroinflammation is a common finding. It is marked by local glial activation, T cell infiltration and systemic immune system activation. The immune system has a prominent role in the pathogenesis of various chronic diseases, hence some of them, including some types of cancer, are successfully targeted by immunotherapeutic approaches. However, various anti-inflammatory or immunosuppressive therapies in amyotrophic lateral sclerosis have failed. This prompted increased scrutiny over the immune-mediated processes underlying amyotrophic lateral sclerosis. Perhaps the biggest conundrum is that amyotrophic lateral sclerosis pathogenesis exhibits features of three otherwise distinct immune dysfunctions-excessive inflammation, autoimmunity and inefficient immune responses. Epidemiological and genome-wide association studies show only minimal overlap between amyotrophic lateral sclerosis and autoimmune diseases, so excessive inflammation is usually thought to be secondary to protein aggregation, mitochondrial damage or other stresses. In contrast, several recently characterized amyotrophic lateral sclerosis-linked mutations, including those in TBK1, OPTN, CYLD and C9orf72, could lead to inefficient immune responses and/or damage pile-up, suggesting that an innate immunodeficiency may also be a trigger and/or modifier of this disease. In such cases, non-selective immunosuppression would further restrict neuroprotective immune responses. Here we discuss multiple layers of immune-mediated neuroprotection and neurotoxicity in amyotrophic lateral sclerosis. Particular focus is placed on individual patient mutations that directly or indirectly affect the immune system, and the mechanisms by which these mutations influence disease progression. The topic of immunity in amyotrophic lateral sclerosis is timely and relevant, because it is one of the few common and potentially malleable denominators in this heterogenous disease. Importantly, amyotrophic lateral sclerosis progression has recently been intricately linked to patient T cell and monocyte profiles, as well as polymorphisms in cytokine and chemokine receptors. For this reason, precise patient stratification based on immunophenotyping will be crucial for efficient therapies.

Mendelian randomization implies no direct causal association between leukocyte telomere length and amyotrophic lateral sclerosis

We employed Mendelian randomization (MR) to evaluate the causal relationship between leukocyte telomere length (LTL) and amyotrophic lateral sclerosis (ALS) with summary statistics from genome-wide association studies (n = ~ 38,000 for LTL and ~ 81,000 for ALS in the European population; n = ~ 23,000 for LTL and ~ 4,100 for ALS in the Asian population). We further evaluated mediation roles of lipids in the pathway from LTL to ALS. The odds ratio per standard deviation decrease of LTL on ALS was 1.10 (95% CI 0.93–1.31, p = 0.274) in the European population and 0.75 (95% CI 0.53–1.07, p = 0.116) in the Asian population. This null association was also detected between LTL and frontotemporal dementia in the European population. However, we found that an indirect effect of LTL on ALS might be mediated by low density lipoprotein (LDL) or total cholesterol (TC) in the European population. These results were robust against extensive sensitivity analyses. Overall, our MR study did not support the direct causal association between LTL and the ALS risk in neither population, but provided suggestive evidence for the mediation role of LDL or TC on the influence of LTL and ALS in the European population.

Smoking and multiple sclerosis risk: a Mendelian randomization study

BACKGROUND

Striking changes in the demographic pattern of multiple sclerosis (MS) strongly indicate an influence of modifiable exposures, which lend themselves well to intervention. It is important to pinpoint which of the many environmental, lifestyle, and sociodemographic changes that have occurred over the past decades, such as higher smoking and obesity rates, are responsible. Mendelian randomization (MR) is an elegant tool to overcome limitations inherent to observational studies and leverage human genetics to inform prevention strategies in MS.

METHODS

We use genetic variants from the largest genome-wide association study for smoking phenotypes (initiation: N = 378, heaviness: N = 55, lifetime smoking: N = 126) and body mass index (BMI, N = 656) and apply these as instrumental variables in a two-sample MR analysis to the most recent meta-analysis for MS. We adjust for the genetic correlation between smoking and BMI in a multivariable MR.

RESULTS

In univariable and multivariable MR, smoking does not have an effect on MS risk nor explains part of the association between BMI and MS risk. In contrast, in both analyses each standard deviation increase in BMI, corresponding to roughly 5 kg/m² units, confers a 30% increase in MS risk.

CONCLUSION

Despite observational studies repeatedly reporting an association between smoking and increased risk for MS, MR analyses on smoking phenotypes and MS risk could not confirm a causal relationship. This is in contrast with BMI, where observational studies and MR agree on a causal contribution. The reasons for the discrepancy between observational studies and our MR study concerning smoking and MS require further investigation.

Epidemiology of amyotrophic lateral sclerosis: an update of recent literature

The cause of amyotrophic lateral sclerosis (ALS) remains unknown for most of the patients with the disease. Epidemiologic studies can help describe disease burden and examine its potential risk factors, providing thereby evidence base for future mechanistic studies. With this review, we aimed to provide a summary of epidemiologic studies published during the past 18 months, which studied the incidence and risk factors for ALS.

Peripheral immune biomarkers and neurodegenerative diseases: A prospective cohort study with 20 years of follow-up

OBJECTIVE

To assess the associations of several blood immune biomarkers with the future risks of amyotrophic lateral sclerosis and Parkinson disease in a prospective cohort study with 20 years of follow-up.

METHODS

The Swedish Apolipoprotein-Related Mortality Risk study is a longitudinal cohort study including 812,073 participants with repeated blood biomarker measurements between 1985 and 1996 and a follow-up until 2011. Using a Cox model, we first estimated hazard ratios of amyotrophic lateral sclerosis and Parkinson disease in relation to leukocytes, immunoglobulin G, haptoglobin, and uric acid. We further described the temporal changes of these biomarkers during the 20 years prior to the diagnosis of these diseases.

RESULTS

A total of 585 incident cases of amyotrophic lateral sclerosis and 3,769 incident cases of Parkinson disease were identified during the follow-up. Increasing concentrations of leukocytes, haptoglobin, and uric acid were associated with a lower risk of Parkinson disease. No statistically significant association was, however, noted between the studied biomarkers and amyotrophic lateral sclerosis. Parkinson disease patients appeared to have lower levels of leukocytes and haptoglobin between 20 and 10 years before diagnosis and lower levels of uric acid during the 20 years before diagnosis, compared to controls, although statistically significant differences were only noted during parts of the respective time intervals after multivariable adjustment. No clear differences were noted between patients with amyotrophic lateral sclerosis and controls.

INTERPRETATION

If verified in studies of independent populations, our findings may suggest a different role of systemic inflammation on the risk of Parkinson disease compared to amyotrophic lateral sclerosis. ANN NEUROL 2019;86:913-926.

Role of cigarette smoking in the development of ischemic stroke and its subtypes: a Mendelian randomization study

Purpose

Numerous studies have indicated that smokers have an increased risk of developing ischemic stroke. However, less is known about the causal relationship between cigarette smoking and ischemic stroke subtypes. In the present study, we aim to determine whether genetically predicted cigarette smoking was associated with subtypes of ischemic stroke using Mendelian randomization (MR).

Patients and methods

We used summary-level genetic association data from the MEGASTROKE consortium, including 438,847 individuals of European ancestry (34,217 cases of ischemic stroke and 404,630 controls). We used 176 single nucleotide polymorphisms as instrumental variables, which were previously identified to be associated with smoking in the Study of the Social Science Genetic Association Consortium (n=518,633). MR analyses were performed using inverse-variance-weighted method, weighted-median method, and MR-Egger regression.

Results

We found that genetically predicted smoking was associated with a higher risk of ischemic stroke (odds ratio (OR): 1.24, 95% CI: 1.10–1.39) and large artery ischemic stroke (OR: 1.52, 95% CI: 1.14–2.02), but not with risk of cardioembolic ischemic stroke or small vessel ischemic stroke. Sensitivity analyses using alternative MR approaches produced similar results.

Conclusion

Genetic predisposition toward smoking is causally associated with a higher incidence of large artery ischemic stroke. Further work is warranted to clarify the underlying mechanism of smoking in the development of large artery ischemic stroke.