MND risk factors: an epidemiological study in the north west of England

Clinical and Lifestyle Factors and Risk of Amyotrophic Lateral Sclerosis: A Population-Based Case-Control Study

Background: Amyotrophic lateral sclerosis (ALS) is a progressive, fatal neurodegenerative disease of the motor neurons. The etiology of ALS remains largely unknown, particularly with reference to the potential environmental determinants. Methods: We performed a population-based case-control study in four provinces from both Northern and Southern Italy in order to assess non-genetic ALS risk factors by collecting through tailored questionnaires information about clinical and lifestyle factors. We estimated ALS risk by calculating odds ratio (OR) with its 95% confidence interval (CI) using unconditional logistic regression models adjusted for sex, age and educational attainment. Results: We recruited 230 participants (95 cases and 135 controls). We found a possible positive association of ALS risk with trauma, particularly head trauma (OR = 2.61, 95% CI 1.19–5.72), electric shock (OR = 2.09, 95% CI 0.62–7.06), and some sports, although at a competitive level only. In addition, our results suggest an increased risk for subjects reporting use of private wells for drinking water (OR = 1.38, 95% CI 0.73–2.27) and for use of herbicides during gardening (OR = 1.95, 95% CI 0.88–2.27). Conversely, there was a suggestion of an inverse association with overall fish consumption (OR = 0.27, 95% CI 0.12–0.60), but with no dose-response relation. Consumption of some dietary supplements, namely those containing amino acids and, in the Southern Italy population, vitamins and minerals such as selenium, seemed associated with a statistically imprecise increased risk. Conclusions: Our results suggest a potential etiologic role a number of clinical and lifestyle factors with ALS risk. However, caution is needed due to some study limitations. These include the small sample size and the low number of exposed subjects, which affect statistical precision of risk estimates, the potential for exposure misclassification, and the uncertainties about mechanisms underpinning the possible association between these factors and disease risk.

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.

Smoking is not a risk factor for sporadic amyotrophic lateral sclerosis in an Australian population

BACKGROUND

Controversy persists as to whether smoking is a risk factor for sporadic amyotrophic lateral sclerosis (SALS), the most common form of sporadic motor neuron disease (SMND). We therefore undertook a large case-control study of smoking and SALS in Australia.

METHODS

Cases and controls were recruited Australia-wide over a 10-year period. SALS and the other subgroups of SMND were categorised on the basis of neurologists' reports. Controls were partners or friends of SMND patients or community volunteers. Individuals filled in a questionnaire regarding smoking habits. A total of 809 patients with SMND (631 with SALS) and 779 controls were included in the study. SALS males and females were analysed separately.

RESULTS

No differences between SALS patients and control groups were found with regard to (1) the odds ratios of ever-smokers, ex-smokers or current smokers compared to never-smokers, (2) the means of numbers of cigarettes per day, years of smoking, pack years or age smoking began or (3) the proportions of their parents who had ever smoked. The proportion of ever-smokers and mean pack years did not differ between the clinical subgroups of SMND or between different sites of SALS onset. Partner smoking did not increase the risk of SMND.

CONCLUSION

This Australian case-control study does not support a link between cigarette smoking and any form of SMND.

Smoking and risk of amyotrophic lateral sclerosis: a pooled analysis of 5 prospective cohorts

BACKGROUND

Cigarette smoking has been proposed as a risk factor for amyotrophic lateral sclerosis (ALS), but epidemiological studies supporting this hypothesis have been small and mostly retrospective.

OBJECTIVE

To prospectively examine the relation between smoking and ALS in 5 well-established large cohorts.

DESIGN

Five prospective cohorts with study-specific follow-up ranging from 7 to 28 years.

SETTING

Academic research.

PATIENTS

Participants in the Nurses' Health Study, the Health Professionals Follow-up Study, the Cancer Prevention Study II Nutrition Cohort, the Multiethnic Cohort, and the National Institutes of Health-AARP (formerly known as the American Association of Retired Persons) Diet and Health Study.

MAIN OUTCOME MEASURES

Amyotrophic lateral sclerosis deaths identified through the National Death Index. In the Nurses' Health Study and the Health Professionals Follow-up Study, confirmed nonfatal incident ALS was also included.

RESULTS

A total of 832 participants with ALS were documented among 562,804 men and 556,276 women. Smokers had a higher risk of ALS than never smokers, with age- and sex-adjusted relative risks of 1.44 (95% confidence interval, 1.23-1.68; P < .001) for former smokers and 1.42 (95% confidence interval, 1.07-1.88; P = .02) for current smokers. Although the risk of ALS was positively associated with pack-years smoked (P < .001), duration of smoking (9% increase for each 10 years of smoking, P = .006), and the number of cigarettes smoked per day (10% increase for each increment of 10 cigarettes smoked per day, P < .001), these associations did not persist when never smokers were excluded. However, among ever smokers, the risk of ALS increased as age at smoking initiation decreased (P = .03).

CONCLUSIONS

Results of this large longitudinal study support the hypothesis that cigarette smoking increases the risk of ALS. The potential importance of age at smoking initiation and the lack of a dose response deserve further investigation.

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.

Genetic susceptibility to environmental toxicants in ALS

Environmental toxicants such as heavy metals, pesticides, and chemicals appear to be risk factors for sporadic amyotrophic lateral sclerosis (SALS). An impaired ability to break down these toxicants because of differences in detoxification genes could underlie some cases of this disease. We therefore examined the frequencies of single nucleotide polymorphisms (SNPs) in 186 SALS patients and 186 controls at the allele, genotype, and haplotype levels for the metallothionein (MT) family of genes, metal transcription factor-1 (MTF-1), and glutathione synthetase (GSS). Exposure to heavy metals, solvents/chemicals, and pesticides/herbicides was assessed by questionnaire, and gene-toxicant interactions were analyzed. An intronic SNP upstream of MT-Ie differed in SALS patients and controls at the allele and genotype levels. Haplotypes covering MT-I isoforms also differed between the two groups. Alleles and genotypes of one MTF-1 SNP differed in female SALS patients. One GSS haplotype interacted with both metals and solvents/chemicals to increase the risk of the disease. Differences in genes involved in handling toxicants, and interactions between toxicants and these genes, appear to be present in some patients with SALS. This suggests that impaired detoxification mechanisms play a role in SALS.

Smoking, Snuff Dipping and the Risk of Amyotrophic Lateral Sclerosis – A Prospective Cohort Study

BACKGROUND

Little is known about the etiology of amyotrophic lateral sclerosis (ALS). The association between cigarette smoking, but not other types of smoking and snuff dipping, and the risk of ALS has been evaluated in several epidemiologic studies. The findings were inconclusive.

METHODS

We studied the association of smoking and snuff dipping with the risk of ALS in the Swedish Construction Workers Cohort, which includes 280,558 male construction workers enrolled between 1978 and 1993 with detailed information on tobacco use. Incident cases of ALS were identified through cross-linkage to the Swedish Inpatient Register. Relative risks and their corresponding 95% confidence intervals (CIs) were estimated using the Cox proportional hazards regression model.

RESULTS

After a mean follow-up duration of 19.6 years, we identified 160 incident cases of ALS through 2004. Compared with non-tobacco use, the relative risk of ALS was 0.8 (95% CI 0.6-1.1) for tobacco smoking and 0.6 (95% CI 0.3-1.5) for snuff dipping, respectively. For tobacco smoking, further stratified analyses of smoking status or types of tobacco smoking did not reveal any excess risks in any strata.

CONCLUSIONS

Our study provides no evidence that smoking or snuff dipping is associated with an increased ALS risk among men.

Amyotrophic Lateral Sclerosis and Exposure to Environmental Toxins: An Australian Case-Control Study

It has been suggested that environmental toxins could be risk factors for sporadic amyotrophic lateral sclerosis (SALS). We therefore analysed epidemiological data on 179 SALS cases and 179 age-, ethnicity- and sex-matched controls in Australia using self-reporting questionnaires. SALS was associated with solvent/chemical exposure (OR = 1.92, 95% CI: 1.26-2.93), overall herbicide/pesticide exposure (OR = 1.57, 95% CI: 1.03-2.41) and industrial herbicide/pesticide exposure (OR = 5.58, 95% CI: 2.07-15.06). Exposure to herbicides/pesticides showed a dose-response effect. All positive findings were more statistically significant in males. These findings support those from northern hemisphere studies, indicating that environmental toxins can be risk factors for SALS.

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.

Cost effectiveness of treatments for amyotrophic lateral sclerosis: a review of the literature

Amyotrophic lateral sclerosis (ALS) is a difficult to diagnose, fatal, progressive degenerative disease with an average survival time of 2 to 5 years. Percutaneous endoscopic gastrotomy (PEG) and bi-level intermittent positive pressure (BIPAP) ventilation may be the major interventions leading to longer survival of patients with ALS. Riluzole has been shown to have modest effects on survival (as opposed to functional) gains and is currently the only drug approved for the treatment of ALS. There is conflicting evidence with regard to the ability of recombinant human insulin-like growth factor (rhIGF-I) to retard ALS progression. Mechanical ventilation (via a tracheostomy tube) is expensive, but is widely used in later stage patients with ALS in the US. A review of nine cost-effectiveness studies of riluzole and one of rhIGF-I found the following: drug costs and survival gains are the major drivers of cost effectiveness; survival gains are estimated from truncated databases with a high degree of uncertainty; more accurate stage-specific utility weights based on patients who agreed to treatment are needed; case incidence-based evaluations should be carried out; cost-effectiveness ratios are insensitive to discount rates; employment and caregiver issues or externalities have been widely ignored; threshold acceptance cost-effectiveness values are ill-defined and evaluations are not generalisable to other countries because of cost and treatment style differences. On account of the high degree of uncertainty pertaining to survival gains and the relatively high costs per life years or quality-adjusted life-years gained, and while acknowledging that not every therapy has to be cost effective (e.g. orphan drugs), it is still inconclusive as to whether or not riluzole or rhIGF-1 can be considered as cost-effective therapies for ALS.