Amyotrophic lateral sclerosis in Sweden in relation to occupation

Geographical clusters of amyotrophic lateral sclerosis and the Bradford Hill criteria

With the aim of shedding further light on the role of environmental factors in amyotrophic lateral sclerosis (ALS) etiology, we hereby conducted a historical narrative review to critically appraise the published reports on ALS geographical clusters using the modern interpretation of the Bradford Hill criteria for causation. Our research hypothesis was that the more criteria were met, the greater was the evidence supporting a causal association. We found that cluster studies that met the greatest number of Bradford's Hill criteria regarded the non-protein amino acid β-N-methylamino-L-alanine (L-BMAA) and exposure to metals and minerals, but the evidence for causation was at best moderate and was poor for other environmental factors. This defective picture might be attributed not only to the methodological approach adopted by published studies, but also to the inherent difficulties in the application of Bradford Hill criteria, due to the complexity of the disease phenotype and the underlying pathogenic mechanisms.

Formaldehyde and Brain Disorders: A Meta-Analysis and Bioinformatics Approach

While there is significant investigation and investment in brain and neurodegenerative disease research, current understanding of the etiologies of illnesses like Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), and brain cancer remains limited. Environmental exposure to the pollutant formaldehyde, an emerging neurotoxin widely used in industry, is suspected to play a critical role in mediating these disorders, although findings are limited and inconsistent. Focusing on highly exposed groups, we performed a meta-analysis of human epidemiological studies of formaldehyde and neurodegenerative disease (N =  19) or brain tumors (N = 12). To assess the biological plausibility of observed associations, we then conducted a bioinformatics analysis using WikiPathways and the Comparative Toxicogenomics Database and identified candidate genes and pathways that may be related to these interactions. We reported the meta-relative risk (meta-RR) of ALS following high exposures to formaldehyde was increased by 78% (meta-RR = 1.78, 95% confidence interval, CI 1.20-2.65). Similarly, the meta-RR for brain cancer was increased by 71% (meta-RR = 1.71; 95% CI 1.07-2.73) among highly exposed individuals. Multiple sensitivity analyses did not reveal sources of heterogeneity or bias. Our bioinformatics analysis revealed that the oxidative stress genes superoxide dismutase (SOD1, SOD2) and the pro-inflammatory marker tumor necrosis factor (TNF) were identified as the top relevant genes, and the folate metabolism, vitamin B12 metabolism, and the ALS pathways were highly affected by formaldehyde and related to the most brain diseases of interest. Further inquiry revealed the two metabolic pathways are also intimately tied with the formaldehyde cycle. Overall, our bioinformatics analysis supports the link of formaldehyde exposure to ALS or brain tumor reported from our meta-analysis. This new multifactorial approach enabled us to both interrogate the robustness of the epidemiological data and identify genes and pathways that may be involved in these interactions, ultimately lending strong evidence and potential biological plausibility for the association between formaldehyde exposure and brain disease.

Amyotrophic lateral sclerosis, occupational exposure to extremely low frequency magnetic fields and electric shocks: a systematic review and meta-analysis

Exposure to extremely low frequency magnetic fields (ELF-MF) and electric shocks occurs in many workplaces and occupations but it is unclear whether any of these exposures cause Amyotrophic lateral sclerosis (ALS). The aim of this systematic review and meta-analysis is to explore whether occupational exposure to ELF-MF and/or electric shocks are risk factor for ALS. We searched PubMed, Embase, and Web of Science databases up to the end of 2019. Pooled risk estimates were calculated using random-effects meta-analysis including exploration of the sources of heterogeneity between studies and publication bias. Twenty-seven publications fulfilled the inclusion criteria. We found a weak, significant, association between occupational exposure to ELF-MF and the risk of ALS (RR_{Pooled estimate}: 1.20; 95%CI: 1.05, 1.38) with moderate to high heterogeneity (I²=66.3%) and indication of publication bias (P_{Egger's test}=0.03). No association was observed between occupational exposure to electric shocks and risk of ALS (RR_{Pooled estimate}: 0.97; 95%CI: 0.80, 1.17) with high heterogeneity (I²=80.5%), and little indication for publication bias (P_{Egger's test}=0.24). The findings indicate that occupational exposure to ELF-MF, but not electric shocks, might be a risk factor for ALS. However, given the moderate to high heterogeneity and potential publication bias, the results should be interpreted with caution.

Associations of Occupational Exposures to Electric Shocks and Extremely Low-Frequency Magnetic Fields With Motor Neurone Disease

In a New Zealand population-based case-control study we assessed associations with occupational exposure to electric shocks, extremely low-frequency magnetic fields (ELF-MF) and motor neurone disease using job-exposure matrices to assess exposure. Participants were recruited between 2013 and 2016. Associations with ever/never, duration, and cumulative exposure were assessed using logistic regression adjusted for age, sex, ethnicity, socioeconomic status, education, smoking, alcohol consumption, sports, head or spine injury, and solvents, and was mutually adjusted for the other exposure. All analyses were repeated stratified by sex. An elevated risk was observed for having ever worked in a job with potential for electric shocks (odds ratio (OR) = 1.35, 95% confidence interval (CI): 0.98, 1.86), with the strongest association for the highest level of exposure (OR = 2.01, 95% CI: 1.31, 3.09). Analysis by duration suggested a nonlinear association: Risk was increased for both short duration (<3 years; OR = 4.69, 95% CI: 2.25, 9.77) and long duration (>24 years; OR = 1.88; 95% CI: 1.05, 3.36) in a job with high level of electric shock exposure, with less pronounced associations for intermediate durations. No association with ELF-MF was found. Our findings provide support for an association between occupational exposure to electric shocks and motor neurone disease but did not show associations with exposure to work-related ELF-MF.

The Relationship between Selected Demographic Factors and Speech Organ Dysfunction in Sporadic ALS Patients

Background and objectives: Speech disorders are observed in 30% of newly diagnosed sporadic amyotrophic lateral sclerosis (ALS) patients. Characterized by a dynamic course, dysfunction of articulation has not so far been well understood. The aim of this study was to analyze the influence of demographic factors (sex, age, duration of the disease) and concomitant diseases (degenerative spine disease, depression, hypertension, hypothyroidism, hyperthyroidism, and allergy) on the functioning of speech organs in ALS patients. Materials and Methods: The study group consisted of 65 patients with sporadic ALS. Patients were examined for articulatory functions by means of the Frenchay Dysarthria Assessment (FDA). Results: 68% of the study sample had spinal disorders. Logistic regression analysis showed that a decline in the functioning of lips, soft palate, length of phonation, and voice loudness was more common among men. Patients diagnosed with degenerative spine disease more often suffered from respiratory disorders, while younger patients (<60 years of age) significantly more often had the impairment of the sentence and spontaneous speech functions. Conclusions: The male gender in patients with ALS is associated with an increased risk of deterioration of the phonation length function. Patients under 60 years of age are associated with more often pronouncing sentences disorders and spontaneous speech disorders.

Occupation and motor neuron disease: a New Zealand case–control study

Objectives

To assess associations between occupation and motor neuron disease (MND).

Methods

We conducted a population-based case–control study with cases (n=321) recruited through the New Zealand Motor Neurone Disease Association and hospital discharge data. Controls (n=605) were recruited from the Electoral Roll. Information on personal and demographic details, lifestyle factors and a full occupational history was collected using questionnaires and interviews. Associations with ever/never employed and employment duration were estimated using logistic regression stratified by sex and adjusted for age, ethnicity, socioeconomic deprivation, education and smoking.

Results

Elevated risks were observed for field crop and vegetable growers (OR 2.93, 95% CI 1.10 to 7.77); fruit growers (OR 2.03, 95% CI 1.09 to 3.78); gardeners and nursery growers (OR 1.96, 95% CI 1.01 to 3.82); crop and livestock producers (OR 3.61, 95% CI 1.44 to 9.02); fishery workers, hunters and trappers (OR 5.62, 95% CI 1.27 to 24.97); builders (OR 2.90, 95% CI 1.41 to 5.96); electricians (OR 3.61, 95% CI 1.34 to 9.74); caregivers (OR 2.65, 95% CI 1.04 to 6.79); forecourt attendants (OR 8.31, 95% CI 1.79 to 38.54); plant and machine operators and assemblers (OR 1.42, 95% CI 1.01 to 2.01); telecommunications technicians (OR 4.2, 95% CI 1.20 to 14.64); and draughting technicians (OR 3.02, 95% CI 1.07 to 8.53). Industries with increased risks were agriculture (particularly horticulture and fruit growing), construction, non-residential care services, motor vehicle retailing, and sport and recreation. Positive associations between employment duration and MND were shown for the occupations fruit growers, gardeners and nursery growers, and crop and livestock producers, and for the horticulture and fruit growing industry.

Conclusions

This study suggests associations between MND and occupations in agriculture and several other occupations.

Shared polygenic risk and causal inferences in amyotrophic lateral sclerosis

OBJECTIVE

To identify shared polygenic risk and causal associations in amyotrophic lateral sclerosis (ALS).

METHODS

Linkage disequilibrium score regression and Mendelian randomization were applied in a large-scale, data-driven manner to explore genetic correlations and causal relationships between >700 phenotypic traits and ALS. Exposures consisted of publicly available genome-wide association studies (GWASes) summary statistics from MR Base and LD-hub. The outcome data came from the recently published ALS GWAS involving 20,806 cases and 59,804 controls. Multivariate analyses, genetic risk profiling, and Bayesian colocalization analyses were also performed.

RESULTS

We have shown, by linkage disequilibrium score regression, that ALS shares polygenic risk genetic factors with a number of traits and conditions, including positive correlations with smoking status and moderate levels of physical activity, and negative correlations with higher cognitive performance, higher educational attainment, and light levels of physical activity. Using Mendelian randomization, we found evidence that hyperlipidemia is a causal risk factor for ALS and localized putative functional signals within loci of interest.

INTERPRETATION

Here, we have developed a public resource (https://lng-nia.shinyapps.io/mrshiny) which we hope will become a valuable tool for the ALS community, and that will be expanded and updated as new data become available. Shared polygenic risk exists between ALS and educational attainment, physical activity, smoking, and tenseness/restlessness. We also found evidence that elevated low-desnity lipoprotein cholesterol is a causal risk factor for ALS. Future randomized controlled trials should be considered as a proof of causality. Ann Neurol 2019;85:470-481.

Occupational Exposures and Neurodegenerative Diseases-A Systematic Literature Review and Meta-Analyses

Objectives: To carry out an integrated and stratified meta-analysis on occupational exposure to electromagnetic fields (EMFs), metals and pesticides and its effects on amyotrophic lateral sclerosis (ALS) and Parkinson's and Alzheimer's disease, and investigate the possibility of publication bias. Methods: In the current study, we updated our recently published meta-analyses on occupational exposures in relation to ALS, Alzheimer's and Parkinson's disease. Based on 66 original publications of good scientific epidemiological standard, according to the Meta-analysis of Observational Studies in Epidemiology (MOOSE) and the Grading of Recommendations, Assessment, Development and Evaluations (GRADE) guidelines, we analysed subgroups by carrying out stratified meta-analyses on publication year, statistical precision of the relative risk (RR) estimates, inspection of the funnel plots and test of bias. Results: Based on 19 studies the weighted RR for occupational exposure to EMFs was 1.26 (95% confidence interval (CI) 1.07⁻1.50) for ALS, 1.33 (95% CI 1.07⁻1.64) for Alzheimer's disease and 1.02 (95% CI 0.83⁻1.26) for Parkinson's disease. Thirty-one studies concerned occupational exposure to pesticides and the weighted RR was 1.35 (95% CI 1.02⁻1.79) for ALS, 1.50 (95% CI 0.98⁻2.29) for Alzheimer's disease and 1.66 (95% CI 1.42⁻1.94) for Parkinson's disease. Finally, 14 studies concerned occupational exposure to metals and only exposure to lead (five studies) involved an elevated risk for ALS or Parkinson's disease and the weighted RR was 1.57 (95% CI 1.11⁻2.20). The weighted RR for all the non-lead exposures was 0.97 (95% CI 0.88⁻1.06). Conclusions: Exposure to pesticides increased the risk of getting the mentioned neurodegenerative diseases by at least 50%. Exposure to lead was only studied for ALS and Parkinson's disease and involved 50% increased risk. Occupational exposure to EMFs seemed to involve some 10% increase in risk for ALS and Alzheimer's disease only.

Amyotrophic Lateral Sclerosis and Occupational Exposures: A Systematic Literature Review and Meta-Analyses

Objectives: We conducted a systematic literature review to identify studies fulfilling good scientific epidemiological standards for use in meta-analyses of occupational risk factors for amyotrophic lateral sclerosis (ALS). Methods: We identified 79 original publications on associations between work and ALS. The MOOSE (Meta-analysis Of Observational Studies in Epidemiology) and GRADE (Grading of Recommendations, Assessment, Development and Evaluations) guidelines were used to ensure high scientific quality, and reliable protocols were applied to classify the articles. Thirty-seven articles fulfilled good scientific standards, while 42 were methodologically deficient and thus were excluded from our meta-analyses. Results: The weighted relative risks for the various occupational exposures were respectively; 1.29 (95% confidence interval (CI): 0.97–1.72; six articles) for heavy physical work, 3.98 (95% CI: 2.04–7.77; three articles) for professional sports, 1.45 (95% CI: 1.07–1.96; six articles) for metals, 1.19 (95% CI: 1.07–1.33; 10 articles) for chemicals, 1.18 (95% CI: 1.07–1.31; 16 articles) for electromagnetic fields or working with electricity, and 1.18 (95% CI: 1.05–1.34; four articles) for working as a nurse or physician. Conclusions: Meta-analyses based only on epidemiologic publications of good scientific quality show that the risk of ALS is statistically significantly elevated for occupational exposures to excessive physical work, chemicals (especially pesticides), metals (especially lead), and possibly also to electromagnetic fields and health care work. These results are not explained by publication bias.

Amyotrophic Lateral Sclerosis and Exposure to Diesel Exhaust in a Danish Cohort

Previous studies have suggested an increased risk of amyotrophic lateral sclerosis (ALS) and other motor neuron diseases for persons in occupations commonly involving exposure to diesel exhaust (DE). In this study, we investigated the association between occupational exposure to DE and odds of ALS. ALS cases were identified from the Danish National Patient Registry (1982-2013) and individually matched to 100 controls per case on the basis of birth year and sex. Using information on occupational history from 1964 onward obtained from the Danish Pension Fund, we estimated cumulative DE exposures using a job exposure matrix. We evaluated associations using conditional logistic regression analyses and stratified the analyses by sex. Using a 10-year lag period, DE exposure was positively associated with ALS among men who had ever been exposed (adjusted odds ratio (aOR) = 1.20, 95% confidence interval (CI): 1.05, 1.38). For men with greater than 50% probability of DE exposure, we observed a positive association between ALS and highest-quartile exposure during the 5-year (aOR = 1.35, 95% CI: 1.07, 1.70) and 10-year (aOR = 1.41, 95% CI: 1.11, 1.79) lag periods. Our study suggests an association between consistently higher exposures to DE and ALS in men, but not in women. These findings support previous reports of associations between ALS and occupations commonly involving DE exposure.

Study of occupation and amyotrophic lateral sclerosis in a Danish cohort

OBJECTIVES

Several manuscripts have proposed associations between amyotrophic lateral sclerosis (ALS) and occupational toxicant exposures-not to mention physical activity and trauma/injury. Some have also reported associations in investigations of specific occupations. Using data from a prospective Danish cohort study, we investigated the association between employment in certain industries and ALS diagnosis.

METHODS

We identified 1826 ALS cases who were 25 years old or less in 1964 and diagnosed from 1982 to 2013 from the Danish National Patient Registry then matched 100 population controls to each case based on birth year and sex. Demographic data were linked to the Danish Pension Fund to determine occupation history. Conditional logistic regression models were adjusted for socioeconomic status, marital status and residential location at the index date.

RESULTS

There was an increase in odds of ALS among men who worked in agriculture, hunting, forestry or fishing (adjusted OR (aOR)=1.21; 95% CI 1.02 to 1.45). There was also a positive association for men employed in construction (aOR=1.21; 95% CI 1.05 to 1.39). In women, a protective association was seen with employment in the cleaning industry (aOR=0.69; 95% CI 0.52 to 0.93).

CONCLUSIONS

Our study shows various occupations with exposure to toxicants, such as diesel exhaust and lead, and strenuous physical activity associated with increased odds of ALS in men. Future studies should have a particular focus on gathering detailed information on physical exertion and toxicant exposures specific to certain job tasks.

Military service and the risk of amyotrophic lateral sclerosis: A meta-analysis

To explore the relationship between the risk of amyotrophic lateral sclerosis and exposure to overall military service, we conducted a search of articles relevant to military service and the risk of ALS that used human subjects and were published in English through 20 May 2016, using Ovid Medline and Embase databases. Studies specially investigating the risk of ALS for Gulf war veterans were excluded. Quality of the cohort and case-control studies was assessed according to the Newcastle-Ottawa Scale (NOS). Analysis of data and publication bias were performed with Review Manager 5.3. A total of 8 case-control studies and 3 cohort studies were included in the meta-analysis. Only two case-control studies were conducted in Japan, comparing to 9 studies conducted in Europe/USA. The NOS scores of all studies were ≥6/9. The risk of ALS was significantly increased in military personnel compared to non-military personnel (pooled OR=1.29, 95% CI: 1.08-1.54, by random-effects model), with a moderate heterogeneity (P=0.01, I²=55%) due to some studies with lower quality, conformed by subgroup and sensitivity analysis. The present meta-analysis supports a positive association between overall military service and the risk of ALS. Additional studies are needed to find out related factors influencing the ALS risk of veterans, especially by gender and for specific geographic regions such as Asia. That would also do some favor to explore the etiology and mechanism of ALS.

Environmental and Occupational Exposures and Amyotrophic Lateral Sclerosis in New England

BACKGROUND

Recent data provide support for the concept that potentially modifiable exposures are responsible for sporadic amyotrophic lateral sclerosis (ALS).

OBJECTIVE

To evaluate environmental and occupational exposures as risk factors for sporadic ALS.

METHODS

We performed a case-control study of ALS among residents of New England, USA. The analysis compared questionnaire responses from 295 patients with a confirmed ALS diagnosis to those of 225 controls without neurodegenerative illness.

RESULTS

Self-reported job- or hobby-related exposure to one or more chemicals, such as pesticides, solvents, or heavy metals, increased the risk of ALS (adjusted OR 2.51; 95% CI 1.64-3.89). Industries with a higher toxicant exposure potential (construction, manufacturing, mechanical, military, or painting) were associated with an elevated occupational risk (adjusted OR 3.95; 95% CI 2.04-8.30). We also identified increases in the risk of ALS associated with frequent participation in water sports, particularly waterskiing (adjusted OR 3.89; 95% CI 1.97-8.44). Occupation and waterskiing both retained independent statistical significance in a composite model containing age, gender, and smoking status.

CONCLUSIONS

Our study contributes to a growing body of literature implicating occupational- and hobby-related toxicant exposures in ALS etiology. These epidemiologic study results also provide motivation for future evaluation of water-body-related risk factors.

Occupational exposures and the risk of amyotrophic lateral sclerosis

OBJECTIVES

To examine the associations of specific occupations and occupational exposures with the risk of amyotrophic lateral sclerosis (ALS) in the Swedish population.

METHODS

A nested case-control study was conducted in Sweden. Patients with ALS diagnosed during 1991-2010 (n=5020) were identified from the National Patient Register and 5 controls per case (n=25 100) were randomly selected from the general Swedish population, individually matched to cases by birth year and sex. Occupational history was obtained from the Swedish censuses in 1970, 1980 and 1990. The Nordic Occupational Cancer Study Job Exposure Matrix was used to identify exposures related to individual occupations. Conditional logistic regression was used to estimate ORs and their 95% CIs.

RESULTS

Higher risk of ALS was associated with precision-tool manufacturing (OR 1.68, 95% CI 1.11 to 2.52) and glass, pottery and tile work (OR 1.76, 95% CI 1.03 to 3.00), whereas lower risk was associated with textile work (OR 0.44, 95% CI 0.21 to 0.91). None of the examined occupational exposures were associated with ALS risk overall. However, among individuals younger than 65 years of age, an association with a higher risk of ALS was found for formaldehyde (OR 1.29, 95% CI 1.00 to 1.65), and an association with a lower risk of ALS was found for methylene chloride (OR 0.49, 95% CI 0.26 to 0.93).

CONCLUSIONS

We identified several occupations and occupational exposures that may be associated with the risk of ALS in Sweden. Occupational history obtained from censuses every 10 years remains a limitation of the study.

Preliminary Results of National Amyotrophic Lateral Sclerosis (ALS) Registry Risk Factor Survey Data

BACKGROUND

The National ALS Registry is made up of two components to capture amyotrophic lateral sclerosis (ALS) cases: national administrative databases (Medicare, Medicaid, Veterans Health Administration and Veterans Benefits Administration) and self-identified cases captured by the Registry's web portal. This study describes self-reported characteristics of U.S. adults with ALS using the data collected by the National ALS Registry web portal risk factor surveys only from October 19, 2010 through December 31, 2013.

OBJECTIVE

To describe findings from the National ALS Registry's web portal risk factor surveys.

MEASUREMENTS

The prevalence of select risk factors among adults with ALS was determined by calculating the frequencies of select risk factors-smoking and alcohol (non, current and former) histories, military service and occupational history, and family history of neurodegenerative diseases such as ALS, Alzheimer's and/or Parkinson's.

RESULTS

Nearly half of survey respondents were ever smokers compared with nearly 41% of adults nationally. Most respondents were ever drinkers which is comparable to national estimates. The majority were light drinkers. Nearly one-quarter of survey respondents were veterans compared with roughly 9% of US adults nationally. Most respondents were retired or disabled. The industries in which respondents were employed for the longest time were Professional and Scientific and Technical Services. When family history of neurodegenerative diseases in first degree relatives was evaluated against our comparison group, the rates of ALS were similar, but were higher for Parkinson's disease, Alzheimer's disease and any neurodegenerative diseases.

CONCLUSIONS

The National ALS Registry web portal, to our knowledge, is the largest, most geographically diverse collection of risk factor data about adults living with ALS. Various characteristics were consistent with other published studies on ALS risk factors and will allow researchers to generate hypotheses for future research.

Physical activity, and physical activity related to sports, leisure and occupational activity as risk factors for ALS: A systematic review

BACKGROUND

Amyotrophic lateral sclerosis (ALS) is considered a multifactorial, multisystem neurodegenerative disease due to an interaction between environmental and genetic factors. This systematic review aims at gathering all available evidence on the association between physical activity (PA) and the risk of ALS.

METHODS

Relevant literature published up to January 2015 was gathered through structured searches on Medline, The Cochrane Library, and the ISI Web of Science databases. Studies considering any type of PA as the main exposure and a diagnosis of ALS or motor neuron disease were selected. Data were extracted in standardized forms, and the quality of included studies was assessed using the Newcastle-Ottawa Scale (NOS).

RESULTS

Bibliographic searches yielded 3168 records. Nineteen case control studies and 7 cohort studies met the inclusion criteria, and were included in the analysis. Evidence on cumulative measures of PA as a risk factor for ALS remain inconclusive. However, cohort studies report a significantly higher number of cases of ALS in professional soccer and American football players, and a slightly increased risk of ALS in varsity athletes.

Extremely Low Frequency Magnetic Field Exposure and Parkinson's Disease--A Systematic Review and Meta-Analysis of the Data

Objective: To examine the association between occupational exposure to extremely-low-frequency magnetic fields (ELF-MF) and Parkinson’s disease. Methods: We systematically searched publications reporting risk estimates of Parkinson’s disease in workers exposed to ELF-MF. Summary relative risks were obtained with random effects meta-analysis. Results: We included 11 studies. To assign exposure, four studies evaluated occupational records, four used census, interview or questionnaire information and three used death certificates. Risk of Parkinson’s disease was not elevated in workers exposed to ELF-MF with a summary relative risk of 1.05, 95% CI 0.98–1.13. Conclusions: Overall, there was no evidence that the exposure to ELF-MF increases the risk of Parkinson’s disease.

Exposure to hazardous air pollutants and the risk of amyotrophic lateral sclerosis

BACKGROUND

Amyotrophic lateral sclerosis (ALS) is a serious and rapidly fatal neurodegenerative disorder with an annual incidence of 1-2.6/100,000 persons. Few known risk factors exist although gene-environment interaction is suspected. We investigated the relationship between suspected neurotoxicant hazardous air pollutants (HAPs) exposure and ALS.

METHODS

A case-control study involving sporadic ALS cases (n = 51) and matched controls (n = 51) was conducted from 2008 to 2011. Geocoded residential addresses were linked to U.S. EPA NATA data (1999, 2002, and 2005) by census tract. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated using conditional logistic regression.

RESULTS

Residential exposure to aromatic solvents significantly elevated the risk of ALS among cases compared to controls in 2002 (OR = 5.03, 95% CI: 1.29, 19.53) and 1999 (OR = 4.27, 95% CI: 1.09, 16.79) following adjustment for education, smoking, and other exposure groups. Metals, pesticides, and other HAPs were not associated with ALS.

CONCLUSIONS

A potential relationship is suggested between residential ambient air aromatic solvent exposure and risk of ALS in this study.

Amyotrophic lateral sclerosis and agricultural environments: a systematic review

The aim of this study was to examine the relationship between the risk of amyotrophic lateral sclerosis (ALS) and exposure to rural environments. Studies were identified through OVID MEDLINE and EMBASE search up to September 2013 using as keywords rural residence, farmers, and pesticide exposure. Twenty-two studies were included for this meta-analysis. Summary odds ratios (ORs) were calculated using random effect model by type of exposure index, and subgroup analyses were conducted according to study design, gender, region, case ascertainment, and exposure assessment. The risk of ALS was significantly increased with pesticide exposure (OR, 1.44; 95% CI, 1.22-1.70) and with farmers (OR, 1.42; 95% CI, 1.17-1.73), but was not significant with rural residence (OR, 1.25; 95% CI, 0.84-1.87). The risk estimates for subgroup analysis between pesticide exposure and ALS indicated a significant positive association with men (OR, 1.96), and in studies using El Escorial criteria for ALS definition (OR, 1.63) and expert judgment for pesticide exposure (OR, 2.04) as well. No significant publication bias was observed. Our findings support the association of pesticide exposure and an increased risk for ALS, stressing that the use of more specific exposure information resulted in more significant associations.

Military service, deployments, and exposures in relation to amyotrophic lateral sclerosis etiology and survival

Rates of amyotrophic lateral sclerosis (ALS) have been reported to be higher among US military veterans, who currently number more than 21 million, but the causal factor(s) has not been identified. We conducted a review to examine the weight of evidence for associations between military service, deployments, and exposures and ALS etiology and survival. Thirty articles or abstracts published through 2013 were reviewed. Although the current evidence suggests a positive association with ALS etiology, it is too limited to draw firm conclusions regarding associations between military service and ALS etiology or survival. Some evidence suggests that deployment to the 1990-1991 Persian Gulf War may be associated with ALS etiology, but there is currently no strong evidence that any particular military exposure is associated with ALS etiology. Future studies should address the limitations of previous ones, such as reliance on mortality as a surrogate for incidence, a dearth of survival analyses, lack of clinical data, low statistical power, and limited exposure assessment. The Genes and Environmental Exposures in Veterans with Amyotrophic Lateral Sclerosis (GENEVA) Study is one such study, but additional research is needed to determine whether military-related factors are associated with ALS and to assess potential prevention strategies.

Clinical perspective on oxidative stress in sporadic amyotrophic lateral sclerosis

Sporadic amyotrophic lateral sclerosis (ALS) is one of the most devastating neurological diseases; most patients die within 3 to 4 years after symptom onset. Oxidative stress is a disturbance in the pro-oxidative/antioxidative balance favoring the pro-oxidative state. Autopsy and laboratory studies in ALS indicate that oxidative stress plays a major role in motor neuron degeneration and astrocyte dysfunction. Oxidative stress biomarkers in cerebrospinal fluid, plasma, and urine are elevated, suggesting that abnormal oxidative stress is generated outside of the central nervous system. Our review indicates that agricultural chemicals, heavy metals, military service, professional sports, excessive physical exertion, chronic head trauma, and certain foods might be modestly associated with ALS risk, with a stronger association between risk and smoking. At the cellular level, these factors are all involved in generating oxidative stress. Experimental studies indicate that a combination of insults that induce modest oxidative stress can exert additive deleterious effects on motor neurons, suggesting that multiple exposures in real-world environments are important. As the disease progresses, nutritional deficiency, cachexia, psychological stress, and impending respiratory failure may further increase oxidative stress. Moreover, accumulating evidence suggests that ALS is possibly a systemic disease. Laboratory, pathologic, and epidemiologic evidence clearly supports the hypothesis that oxidative stress is central in the pathogenic process, particularly in genetically susceptive individuals. If we are to improve ALS treatment, well-designed biochemical and genetic epidemiological studies, combined with a multidisciplinary research approach, are needed and will provide knowledge crucial to our understanding of ALS etiology, pathophysiology, and prognosis.

Environmental and occupational risk factors for amyotrophic lateral sclerosis: a case-control study

BACKGROUND/AIMS

Environmental and occupational exposures are implicated as risk factors for amyotrophic lateral sclerosis (ALS), the etiology of which is largely unknown, although no causal relationships have been established.

OBJECTIVE

The aim of the study was to evaluate the associations of personal risk factors and self-reported environmental and occupational exposures with risk of ALS.

METHODS

The cases involved ALS patients (n = 66) identified from major neurological centers in Pittsburgh and Philadelphia, Pa., USA, from 2008 to 2010. The age-, race- and sex-matched controls included outpatient hospital and population-based controls (n = 66). A detailed questionnaire obtaining data on occupation, vocational and avocational exposure as well as personal lifestyle factors was administered.

RESULTS

Occupational exposure to metals (odds ratio, OR = 3.65; 95% CI: 1.15, 11.60) and pesticides (OR = 6.50; 95% CI: 1.78, 23.77) was related to increased risk of ALS after controlling for smoking and education. No associations were found for occupational exposure to organic or aromatic solvents.

CONCLUSION

Workers exposed to metals and pesticides may be at greater risk of ALS. Future research should involve more accurate exposure assessment through the use of job exposure matrices, confirmation of occupation and biomarkers.

Different occupations associated with amyotrophic lateral sclerosis: is diesel exhaust the link?

The cause of sporadic amyotrophic lateral sclerosis (SALS) remains unknown. We attempted to find out if occupational exposure to toxicants plays a part in the pathogenesis of this disease. In an Australia-wide case-control study we compared the lifetime occupations of 611 SALS and 775 control individuals. Occupations were coded using country-specific as well as international classifications. The risk of SALS for each occupation was calculated with odds ratios using logistic regression. In addition, the literature was searched for possible toxicant links between our findings and previously-reported occupational associations with SALS. Male occupations in our study that required lower skills and tasks tended to have increased risks of SALS, and conversely, those occupations that required higher skills and tasks had decreased risks of SALS. Of all the occupations, only truck drivers, where exposure to diesel exhaust is common, maintained an increased risk of SALS throughout all occupational groups. Another large case-control study has also found truck drivers to be at risk of SALS, and almost two-thirds of occupations, as well as military duties, that have previously been associated with SALS have potential exposure to diesel exhaust. In conclusion, two of the largest case-control studies of SALS have now found that truck drivers have an increased risk of SALS. Since exposure to diesel exhaust is common in truck drivers, as well as in other occupations that have been linked to SALS, exposure to this toxicant may underlie some of the occupations that are associated with SALS.

Association between extremely low-frequency electromagnetic fields occupations and amyotrophic lateral sclerosis: a meta-analysis

Objectives

To estimate the relationship between exposure to extremely low-frequency electromagnetic fields (ELF-EMF) and the risk of amyotrophic lateral sclerosis (ALS) by a meta-analysis.

Methods

Through searching PubMed databases (or manual searching) up to April 2012 using the following keywords: “occupational exposure”, “electromagnetic fields” and “amyotrophic lateral sclerosis” or “motor neuron disease”, seventeen studies were identified as eligible for this meta-analysis. The associations between ELF-EMF exposure and the ALS risk were estimated based on study design (case-control or cohort study), and ELF-EMF exposure level assessment (job title or job-exposure matrix). The heterogeneity across the studies was tested, as was publication bias.

Results

Occupational exposure to ELF-EMF was significantly associated with increased risk of ALS in pooled studies (RR = 1.29, 95%CI = 1.02–1.62), and case-control studies (OR = 1.39, 95%CI = 1.05–1.84), but not cohort studies (RR = 1.16, 95% CI = 0.80–1.69). In sub-analyses, similar significant associations were found when the exposure level was defined by the job title, but not the job-exposure matrix. In addition, significant associations between occupational exposure to ELF-EMF and increased risk of ALS were found in studies of subjects who were clinically diagnosed but not those based on the death certificate. Moderate heterogeneity was observed in all analyses.

Conclusions

Our data suggest a slight but significant ALS risk increase among those with job titles related to relatively high levels of ELF-EMF exposure. Since the magnitude of estimated RR was relatively small, we cannot deny the possibility of potential biases at work. Electrical shocks or other unidentified variables associated with electrical occupations, rather than magnetic-field exposure, may be responsible for the observed associations with ALS.

Epidemiology of amyotrophic lateral sclerosis patients in a centre in Buenos Aires

Sporadic amyotrophic lateral sclerosis (sALS) is considered a multifactorial disease with genetic and environmental factors causing motor neuron degeneration.

OBJECTIVE

To describe the epidemiological and occupational characteristics of patients with sALS who attended the Ramos Mejía Hospital at Buenos Aires, Argentina.

METHOD

We analyzed the medical records of sALS patients diagnosed between 2001 and 2008. All occupations were coded according to the International Standard Classification of Occupation (ISCO).

RESULTS

187 patients were assessed, 38.5% were women and 61.5% men. Mean age at diagnosis was 55 years. 16% of them came from rural areas; 68% of the studied population had no health insurance. 40% were employed in elementary occupations, 19 were technicians and 8 handicraftsmen.

CONCLUSION

The most represented profession was elementary occupation. A large proportion of patients came from rural areas, which might suggest an increased risk of environmental exposure to an unknown agent in those regions.

Effects of gender in amyotrophic lateral sclerosis

BACKGROUND

There is evidence that amyotrophic lateral sclerosis (ALS), also known as motor neuron disease (MND), is more common in men than in women and that gender influences the clinical features of the disease. The causes of this are unknown.

OBJECTIVE

This review examines the gender differences that are found in ALS and postulates reasons for these differences.

METHODS

A literature review of PubMed (with no date limits) was performed to find information about gender differences in the incidence, prevalence, and clinical features of ALS, using the search terms ALS or MND and gender or sex, ALS prevalence, and SOD1 mice and gender. Articles were reviewed for information about gender differences, together with other articles that were already known to the authors.

RESULTS

The incidence and prevalence of ALS are greater in men than in women. This gender difference is seen in large studies that included all ALS patients (sporadic and familial), but is not seen when familial ALS is studied independently. Men predominate in the younger age groups of patients with ALS. Sporadic ALS has different clinical features in men and women, with men having a greater likelihood of onset in the spinal regions, and women tending to have onset in the bulbar region. Gender appears to have no clear effect on survival. In animals with superoxide dismutase 1 (sod1) mutations, sex does affect the clinical course of disease, with earlier onset in males. Possible reasons for the differences in ALS between men and women include different exposures to environmental toxins, different biological responses to exogenous toxins, and possibly underlying differences between the male and female nervous systems and different abilities to repair damage.

CONCLUSIONS

There is a complex interaction between gender and clinical phenotypes in ALS. Understanding the causes of the gender differences could give clues to processes that modify the disease.

What we truly know about occupation as a risk factor for ALS: a critical and systematic review

Occupational and environmental exposures may contribute to the risk of developing sporadic amyotrophic lateral sclerosis (ALS). To summarize the available evidence, a systematic review of the literature on occupation as a potential determinant of ALS was performed according to the MOOSE guidelines. From MEDLINE, EMBASE, CINAHL, and Cochrane databases, selected studies were methodologically appraised according to Armon's classification system for ALS risk factor studies. Each occupation studied was reclassified according to the International Standard Classification of Occupations (ISCO-88). The vote-counting method was applied to summarize the data. Of 3773 potentially relevant studies, 51 were initially included. Of these, 12 studies provided risk estimates for individual occupations--one case-control, two register-based case-control, and nine register-based cohort studies. All studies fell into Armon's level of evidence class IV, indicating methodological limitations. Due to the heterogeneity of study methodology, data could not be pooled. The vote-counting method revealed several candidate occupations: veterinarians and other health workers, athletes, hairdressers, power-production plant, electrical and military workers. However, well designed studies with standardized assessment of occupation are needed to provide a more definitive answer about exogenous risk factors of ALS.

Workplace exposures and the risk of amyotrophic lateral sclerosis

BACKGROUND

Occupation has been suggested to play a role in amyotrophic lateral sclerosis (ALS) etiology, but detailed information on the importance of specific workplace exposures is lacking.

OBJECTIVES

Our aim was to assess the relationship between workplace exposures and the risk of ALS and to evaluate potential interactions between these exposures and smoking.

METHODS

We conducted a case-control study in New England between 1993 and 1996, comprising 109 cases and 253 controls who completed a structured interview covering occupations and workplace exposures. Unconditional logistic regression models were used to estimate the odds ratios (ORs) and 95% confidence intervals (CIs) for ALS. Analyses were conducted among the entire study population and after stratification by smoking.

RESULTS

We observed a higher risk of ALS for construction workers excluding supervisors (OR = 2.9; 95% CI, 1.2-7.2) and precision metal workers (OR = 3.5; 95% CI, 1.2-10.5). Self-reported exposures to paint strippers; cutting, cooling, or lubricating oils; antifreeze or coolants; mineral or white spirits; and dry cleaning agents each appeared to be associated with a 60-90% higher risk. Specific chemicals related to a > 50% increase in risk of ALS included aliphatic chlorinated hydrocarbons, glycols, glycol ethers, and hexane. Relative risks associated with these workplace exposures and chemicals were greater among nonsmokers and persisted in mutually adjusted models.

CONCLUSIONS

Our data suggest that certain occupations and workplace exposures may be associated with increased risk of ALS. These results need to be confirmed in independent populations.

Analysis of factors that modify susceptibility and rate of progression in amyotrophic lateral sclerosis (ALS)

We conducted case-control and prospective longitudinal studies to examine risk factors and predictors of disease progression for ALS. Ninety-five subjects with ALS and 106 healthy control subjects were enrolled. All subjects completed a risk factor questionnaire at enrollment. The ALS subjects were prospectively followed for one year to define factors that influence the rate of disease progression, measured by rate of change in percent predicted forced vital capacity (%FVC) and the ALS functional rating scale (ALSFRS) score. The association of each potential risk factor with ALS was determined using univariate logistic regression. A random slope model was used to determine the association of each risk factor with disease progression. The demographic characteristics of ALS subjects and controls at enrollment did not differ. Significant risk factors for ALS included reported exposure to lead (p = 0.02) and pesticides (p = 0.03). Disease progression was faster in the ALS subjects having bulbar onset and a shorter time period between onset of symptoms and diagnosis. Pertinent variables not associated with either causation or progression of ALS included physical activity, cigarette smoking and a history of physical trauma or other clinical disorders.

[Exogenous risk factors in sporadic ALS: a review of the literature]

The latest reviews of the literature devoted to the epidemiology of ALS all agree that exogenic risk factors play a role in sporadic ALS. Nevertheless, there is no convincing evidence demonstrating in a reproducible manner an association between an environmental risk factor and ALS. This discordance is mainly explained by methodological skews. Over the last ten years, exogenic factors have been analyzed within the framework of specific lifestyle factors such as place of residence, smoking or not, or certain eating practices. The most recent work suggests that interactions between genetic and environmental factors depend on the age at exposure and the duration of exposure. The objectives of this general review is: to analyze the principal case-control studies, historical cohort studies or mortality studies which looked at the associations between an environmental factor and ALS, to present main results of studies having analyzed lifestyles in relation to one or more exogenic factors, and to discuss the limitations of epidemiologic studies on ALS.

Mortality from Alzheimer's, motor neuron and Parkinson's disease in relation to magnetic field exposure: findings from the study of UK electricity generation and transmission workers, 1973-2004

BACKGROUND

There are a number of reports linking magnetic field exposure to increased risks of Alzheimer's disease and motor neuron disease.

METHODS

The mortality experienced by a cohort of 83 997 employees of the former Central Electricity Generating Board of England and Wales was investigated for the period 1973-2004. All employees were employed for at least six months with some employment in the period 1973-82. Computerised work histories were available for 79 972 study subjects for the period 1971-93. Information on job and facility (location) were used to estimate exposures to magnetic fields. Two analytical approaches were used to evaluate risks, indirect standardisation (n = 83 997) and Poisson regression (n = 79 972).

RESULTS

Based on serial mortality rates for England and Wales, deaths from Alzheimer's disease and motor neuron disease were unexceptional. There was an excess of deaths from Parkinson's disease of borderline significance. No statistically significant trends were shown for risks of any of these diseases to increase with lifetime cumulative exposure to magnetic fields (RR per 10 μT-y: Alzheimer's disease 1.10 (95% CI 0.90 to 1.33); motor neuron disease 1.06 (95% CI 0.86 to 1.32); Parkinson's disease 0.88 (95% CI 0.74 to 1.05))

CONCLUSIONS

There is no convincing evidence that UK electricity generation and transmission workers have suffered increased risks from neurodegenerative diseases as a consequence of exposure to magnetic fields.

Prospective study of occupation and amyotrophic lateral sclerosis mortality

Occupational exposures are suspected of contributing to the risk of amyotrophic lateral sclerosis (ALS), but results of epidemiologic studies have been inconsistent. The authors prospectively assessed the relation between occupation and ALS mortality among more than 1 million participants in the Cancer Prevention Study II of the American Cancer Society. Follow-up from 1989 through 2002 identified 507 ALS deaths among men and 430 among women. Adjusted rate ratios were calculated by using Mantel-Haenszel weights and Cox proportional hazards. Among men, elevated ALS mortality was found for programmers (rate ratio = 4.55, 95% confidence interval: 1.46, 14.2; p = 0.009) and laboratory technicians (rate ratio = 1.96, 95% confidence interval: 1.04, 3.66; p = 0.04). Occupations previously associated with increased risk of ALS for which no increased risk was found included farmers, electricians, and welders, although the numbers of electricians (eight ALS deaths) and welders (two ALS deaths) were small. Among women, only machine assemblers had significantly increased ALS mortality (rate ratio = 2.81, 95% confidence interval: 1.05, 7.53; p = 0.04). Results, which suggest that male programmers and laboratory technicians and female machine assemblers may be at increased risk of death from ALS, should be interpreted cautiously, however, because they are based on small numbers.

Amyotrophic lateral sclerosis mortality in the United States, 1979-2001

The etiology of nonfamilial amyotrophic lateral sclerosis (ALS) remains unknown. Earlier studies have suggested an increase in the incidence of ALS over time. We performed a retrospective analysis of ALS-associated death rates and trends in the United States for 1979-2001 using death records from the national multiple cause-of-death database. The US average annual age-adjusted ALS death rate was 1.84 per 100,000 persons for 1979 through 1998. Most deaths were among adults > or =65 years of age and the median age at death was 67 years. A small overall increase in the death rate was observed primarily between 1979 and 1983, with a subsequent plateau. This slight change in the overall rate reflected apparent increases in the rates among those persons > or =65 years of age, particularly women, and persons in the 20- to 49-year-old age group. The ALS-associated death rate appeared to differ by geographic area, with a higher occurrence among most northern states. Our findings suggest that the epidemiology of ALS-associated deaths in the United States demonstrated small increases in the overall age-adjusted death rate and in the death rates among elderly women and adults 20-49 years of age. Subpopulations at higher risk for ALS were males, whites, persons > or =65 years of age, and residents of northern states. This study provides information for further studies to examine the epidemiology and risk factors associated with ALS.

Amyotrophic Lateral Sclerosis

This chapter focuses on amyotrophic lateral sclerosis (ALS), the most common motor neuron disease. It discusses the three major forms of ALS: sporadic ALS, the familial or hereditary form of ALS, and the western Pacific (Mariana Islands) form. Considerable progress has been made in recent years on identifying genetic loci responsible for Mendelian forms of ALS; this evidence is summarized. The potential importance of geographic clusters is discussed, with particular emphasis on the western Pacific form of ALS because it often occurs in association with a parkinsonism and/or dementia complex (PDC). The incidence of Western Pacific ALS peaked and then declined in the mid-20th century, which strongly implicated an environmental cause. The chapter also presents detailed information regarding putative risk factors for sporadic ALS, which includes environmental toxicants, skeletal trauma, cigarette smoking, diet, and vigorous physical activity.

Occupational magnetic field exposure and neurodegenerative disease

BACKGROUND

Several studies have identified occupational exposure to extremely low-frequency electromagnetic fields (EMF) as a potential risk factor for neurodegenerative disease, but the evidence is contradictory and inconclusive.

METHODS

We conducted a cohort study to explore these associations. We studied all economically active individuals in the Swedish 1980 census (4,812,646 subjects), and followed them for neurodegenerative disease mortality from 1981 through 1995. Information about occupation was available for 1970 and 1980. A job-exposure matrix based on magnetic field measurements was used to assess EMF exposure.

RESULTS

An increased risk of Alzheimer's disease mortality was observed among men exposed both in 1970 and 1980 (relative risk = 2.3; 95% confidence interval = 1.6-3.3 for exposure >/=0.5 microT). The associations were most pronounced for early-onset Alzheimer's disease mortality or with follow-up limited to 10 years after the last known occupation. Amyotrophic lateral sclerosis was not associated with EMF exposure, but the risk estimate with "electrical and electronics work" was 1.4 (95% confidence interval = 1.1-1.9).

CONCLUSIONS

Our study gives some support to the hypothesis that EMF exposure increases the risk of early-onset Alzheimer's disease, and suggests that magnetic field exposure may represent a late-acting influence in the disease process. Electric shock is an unlikely explanation for the increased risk of amyotrophic lateral sclerosis in "electrical and electronics work" in this study.

Association between occupational exposure to power frequency electromagnetic fields and amyotrophic lateral sclerosis: a review

BACKGROUND

For the past two decades, there has been concern over electromagnetic exposure and human health. While most research has focused on cancer and reproductive outcomes, there is interest in the relationship between electromagnetic fields (EMF) and neurodegenerative diseases.

METHODS

We review epidemiological findings and evidence regarding the association between occupational exposure to power frequency EMFs and amyotrophic lateral sclerosis (ALS). Medline was searched for citations related to occupational hazards and ALS, literature reviews and epidemiological evaluations.

RESULTS

Nine out of the ten epidemiological studies that have been conducted on the risk of ALS in relation to occupational exposure to EMF show moderate to strong relative risk estimates that supported a link between them. Although data from these studies was consistent, the causal inference to a link between EMF exposure and ALS is restricted mainly due to the lack of direct information on EMF exposure and incomplete consideration of the other potential risk factors for ALS at workplaces. For instance, electric shock, in particular, is more common in electrical occupations than in any other occupations.

CONCLUSIONS

This review concludes that further studies should consider investigating the separate effect of EMF exposure and electrical shocks to make more specific interpretations. On-site measurements of EMF should be conducted to include information on EMF exposure from residences as well as workplaces to improve exposure assessment.