Risk factors for motor neuron disease: a case-control study based on patients from the Scottish Motor Neuron Disease Register

Occupational neurologic disorders in Korea

This article presents a schematic review of the clinical manifestations of occupational neurologic disorders in Korea and discusses the toxicologic implications of these conditions. Vascular encephalopathy, parkinsonism, chronic toxic encephalopathy, cerebellar dysfunction, peripheral neuropathy, and neurodegenerative diseases are common presentations of occupational neurotoxic syndromes in Korea. Few neurotoxins cause patients to present with pathognomic neurologic syndrome. Detailed neurologic examinations and categorization of the clinical manifestations of neurologic disorders will improve the clinical management of occupational neurologic diseases. Physicians must be aware of the typical signs and symptoms of possible exposure to neurotoxins, and they should also pay attention to less-typical, rather-vague symptoms and signs in workers because the toxicologic characteristics of occupational neurologic diseases in Korea have changed from typical patterns to less-typical or equivocal patterns. This shift is likely to be due to several years of low-dose exposure, perhaps combined with the effects of aging, and new types of possibly toxicant-related neurodegenerative diseases. Close collaboration between neurologists and occupational physicians is needed to determine whether neurologic disorders are work-related.

Association between blood lead and the risk of amyotrophic lateral sclerosis

The authors conducted a 2003-2007 case-control study including 184 cases and 194 controls to examine the association between blood lead and the risk of amyotrophic lateral sclerosis (ALS) among US veterans and to explore the influence on this association of bone turnover and genetic factors related to lead toxicokinetics. Blood lead, plasma biomarkers of bone formation (procollagen type 1 amino-terminal peptide (PINP)) and resorption (C-terminal telopeptides of type 1 collagen (CTX)), and the K59N polymorphism in the delta-aminolevulinic acid dehydratase gene, ALAD, were measured. Odds ratios and 95% confidence intervals for the association of blood lead with ALS were estimated with unconditional logistic regression after adjustment for age and bone turnover. Blood lead levels were higher among cases compared with controls (P < 0.0001, age adjusted). A doubling of blood lead was associated with a 1.9-fold increased risk of ALS (95% confidence interval: 1.3, 2.7) after adjustment for age and CTX. Additional adjustment for PINP did not alter the results. Significant lead-ALS associations were observed in substrata of PINP and CTX levels. The K59N polymorphism in the ALAD gene did not modify the lead-ALS association (P = 0.32). These results extend earlier findings by accounting for bone turnover in confirming the association between elevated blood lead level and higher risk of ALS.

Downregulation of genes with a function in axon outgrowth and synapse formation in motor neurones of the VEGFdelta/delta mouse model of amyotrophic lateral sclerosis

Background

Vascular endothelial growth factor (VEGF) is an endothelial cell mitogen that stimulates vasculogenesis. It has also been shown to act as a neurotrophic factor in vitro and in vivo. Deletion of the hypoxia response element of the promoter region of the gene encoding VEGF in mice causes a reduction in neural VEGF expression, and results in adult-onset motor neurone degeneration that resembles amyotrophic lateral sclerosis (ALS). Investigating the molecular pathways to neurodegeneration in the VEGF^δ/δ mouse model of ALS may improve understanding of the mechanisms of motor neurone death in the human disease.

Results

Microarray analysis was used to determine the transcriptional profile of laser captured spinal motor neurones of transgenic and wild-type littermates at 3 time points of disease. 324 genes were significantly differentially expressed in motor neurones of presymptomatic VEGF^δ/δ mice, 382 at disease onset, and 689 at late stage disease. Massive transcriptional downregulation occurred with disease progression, associated with downregulation of genes involved in RNA processing at late stage disease. VEGF^δ/δ mice showed reduction in expression, from symptom onset, of the cholesterol synthesis pathway, and genes involved in nervous system development, including axonogenesis, synapse formation, growth factor signalling pathways, cell adhesion and microtubule-based processes. These changes may reflect a reduced capacity of VEGF^δ/δ mice for maintenance and remodelling of neuronal processes in the face of demands of neural plasticity. The findings are supported by the demonstration that in primary motor neurone cultures from VEGF^δ/δ mice, axon outgrowth is significantly reduced compared to wild-type littermates.

Conclusions

Downregulation of these genes involved in axon outgrowth and synapse formation in adult mice suggests a hitherto unrecognized role of VEGF in the maintenance of neuronal circuitry. Dysregulation of VEGF may lead to neurodegeneration through synaptic regression and dying-back axonopathy.

Association of ALS with head injury, cigarette smoking and APOE genotypes

OBJECTIVE

An increased risk of ALS has been reported for US veterans, but the cause is unknown. Since head injury and cigarette smoking are two previously implicated environmental risk factors that are more common in military than civilian study populations, we tested their association with ALS in a US veteran study population.

METHODS

We used logistic regression to examine the association of ALS with head injury and cigarette smoking in 241 incident cases and 597 controls. Since APOE is a plausible ALS candidate gene, we also tested its main effect and its statistical interaction with these environmental exposures.

RESULTS

Cigarette smoking was not associated with ALS in this predominantly male and Caucasian population. Veterans who had experienced head injuries during the last 15years before the reference date had an adjusted odds ratio of 2.33 (95% confidence interval 1.18-4.61), relative to veterans without any head injuries. This association was strongest in APOE-4 carriers.

CONCLUSIONS

Our results add to the body of evidence suggesting that head injuries may be a risk factor for multiple neurodegenerative diseases, including ALS. We hypothesize that the strength of association between head injuries and ALS may depend upon APOE genotype.

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.

Genes and Environmental Exposures in Veterans with Amyotrophic Lateral Sclerosis: the GENEVA study. Rationale, study design and demographic characteristics

Recent reports of a potentially increased risk of amyotrophic lateral sclerosis (ALS) for veterans deployed to the 1990-1991 Persian Gulf War prompted the Department of Veterans Affairs to establish a National Registry of Veterans with ALS, charged with the goal of enrolling all US veterans with a neurologist-confirmed diagnosis of ALS. The Genes and Environmental Exposures in Veterans with ALS study (GENEVA) is a case-control study presently enrolling cases from the Department of Veterans Affairs registry and a representative sample of veteran controls to evaluate the joint contributions of genetic susceptibility and environmental exposures to the risk of sporadic ALS. The GENEVA study design, recruitment strategies, methods of collecting DNA samples and environmental risk factor information are described here, along with a summary of demographic characteristics of the participants (537 cases, 292 controls) enrolled to date.

[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.

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.

Head injury and amyotrophic lateral sclerosis

Recent data showed that soccer players in Italy had an unusually high risk of amyotrophic lateral sclerosis (ALS) and that repeated head trauma might have contributed to this increase. The authors examined whether head injury was related to ALS risk in a case-control study of 109 New England ALS cases diagnosed in 1993-1996 and 255 matched controls. They also conducted a meta-analysis of the published literature. Overall, ever having experienced a head injury was nonsignificantly associated with a higher ALS risk. When compared with persons without a head injury, a statistically significant ALS risk elevation was found for participants with more than one head injury (odds ratio (OR) = 3.1, 95 percent confidence interval (CI): 1.2, 8.1) and patients who had had a head injury during the past 10 years (OR = 3.2, 95 percent CI: 1.0, 10.2). For participants who had had multiple head injuries with the latest occurring in the past 10 years, risk was elevated more than 11-fold. The meta-analysis also indicated a moderately elevated risk of ALS among persons with previous head injuries (OR = 1.7, 95 percent CI: 1.3, 2.2). In this study population, physical injuries to other body parts, including the trunk, arms, or legs, were not related to ALS risk. These data support the notion that head injury may increase the risk of ALS.

An epidemiologic investigation of amyotrophic lateral sclerosis in Jefferson County, Missouri, 1998-2002

Amyotrophic lateral sclerosis (ALS) cases diagnosed between 1998 and 2002 were identified to study ALS prevalence and spatial clustering in Jefferson County, Missouri, where an active lead smelter is located. The study used the El Escorial criteria for ALS diagnosis, the capture-recapture analysis for ALS case ascertainment, and the spatial scan statistic for cluster analysis. The estimated crude prevalence of ALS in Jefferson County was 3.9 per 100,000 population (95% CI, 1.7-7.7) at the time point on December 31, 2002. After age-adjustment to the 2002 U.S. population, the prevalence was 4.2 per 100,000 (95% CI, 1.9-6.6). This prevalence estimate was comparable to recent prevalence estimates from Western Europe. A small but significant cluster (p=0.04) was detected around the smelter area. An ALS registry utilizing outpatient, inpatient, and death certificate data is needed to provide comprehensive information for ALS case ascertainment. Etiologic studies are needed to assess whether living in proximity to a lead smelter is associated with the development of ALS.

Paraoxonase promoter and intronic variants modify risk of sporadic amyotrophic lateral sclerosis

BACKGROUND

The paraoxonases, PON1-3, play a major protective role both against environmental toxins and as part of the antioxidant defence system. Recently, non-synonymous coding single nucleotide polymorphisms (SNPs), known to lower serum PON activity, have been associated with sporadic ALS (SALS) in a Polish population. A separate trio based study described a detrimental allele at the PON3 intronic variant INS2+3651 (rs10487132). Association between PON gene cluster variants and SALS requires external validation in an independent dataset.

AIMS

To examine the association of the promoter SNPs PON1(-162G>A) and PON1(-108T>C); the non-synonymous functional SNPs PON1(Q192R and L55M) and PON2(C311S and A148G); and the intronic marker PON3(INS2+3651A>G), with SALS in a genetically homogenous population.

METHODS

221 Irish patients with SALS and 202 unrelated control subjects were genotyped using KASPar chemistries. Statistical analyses and haplotype estimations were conducted using Haploview and Unphased software. Multiple permutation testing, as implemented in Unphased, was applied to haplotype p values to correct for multiple hypotheses.

RESULTS

Two of the seven SNPs were associated with SALS in the Irish population: PON1(55M) (OR 1.52, p = 0.006) and PON3(INS2+3651 G) (OR 1.36, p = 0.03). Two locus haplotype analysis showed association only when both of these risk alleles were present (OR 1.7, p = 0.005), suggesting a potential effect modification. Low functioning promoter variants were observed to influence this effect when compared with wild-type.

CONCLUSIONS

These data provide additional evidence that genetic variation across the paroxanase loci may be common susceptibility factors for SALS.

Electrical injury and amyotrophic lateral sclerosis: a systematic review of the literature

Electrical injury may act as a potential precipitating or risk factor for amyotrophic lateral sclerosis (ALS). A systematic review of the literature was undertaken to assess the relationship between electrical injury and the development of ALS. Information for the review was obtained using five medical databases, and from manual searching of individual papers. Patients presenting with a neurological syndrome after electrical injury, including lightning, were included and classified into four categories: ALS; progressive upper motor neurone (UMN) syndrome; progressive lower motor neurone (LMN) syndrome; and non-progressive syndrome. Linear regression and chi2 testing were used for analysis of the data. 96 individuals, comprising 44 with ALS, 1 with a progressive UMN syndrome, 7 with a progressive LMN syndrome and 44 with a non-progressive syndrome, were identified from 31 papers with publication dates between 1906 and 2002. The median interval between electrical injury and disease onset was 2.25 years for all progressive syndromes and just over 1 week for the non-progressive syndrome. The more severe the shock (excluding lightning), the more likely individuals were to have a non-progressive motor syndrome. A non-progressive spinal cord syndrome is associated with more severe electrical injury. Overall, the evidence reviewed does not support a causal relationship between ALS and electric shock.

A case of amyotrophic lateral sclerosis in electronic parts manufacturing worker exposed to lead

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease affecting the motor neurons of the spinal cord and brain. Although the definite etiology of ALS remains unclear, occupational or environmental exposures have been considered as one of the potential causes of ALS. Here, we report the case of a patient with ALS who used to work in a factory manufacturing electronic parts and has evidence of acute exposure to lead in excess. A 39-year-old man visited a neurology clinic with symptoms of progressive limb weakness and spasticity, which began 2 years ago. Upon neurological examination, symptoms of atrophy, spasticity and fasciculation of the lower extremities were evident. There were no signs of impairment of the cranial nerves, and cognitive and sensory functions were normal. Complete blood counts, blood chemistries and urinalysis were normal. Serial electromyography showed progressive denervative changes, which were consistent with motor neuron diseases. ALS was diagnosed according to the standard of the "Diagnostic criteria of the World Federation of Neurology". The patient was handling lead oxide (PbO) for development of positive temperature coefficient (PTC) thermist, without being provided with proper respiratory protective equipment. Blood lead level of the patient was measured at 30.86 microg/dL 6 months after he quit his job. Bone lead levels from X-ray fluorescence (XRF) were below the normal range (3 ppm). Blood lead level of his co-workers at the same workplace were above the ACGIH recommended biological exposure index (BEI: 30 microg/dL). We speculated that the ALS in this case was related to excessive exposure to lead.

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.

Horses on pasture may be affected by equine motor neuron disease

REASONS FOR PERFORMING STUDY

Equine motor neuron disease (EMND) was diagnosed in 3 horses maintained on lush, grass-based pasture. This contrasted with North American studies which identified limited or no access to green herbage as an important risk factor for EMND.

HYPOTHESIS

Grazing horses that have an apparently adequate intake of pasture herbage to meet normal equine vitamin E requirements can develop EMND.

METHODS

Owners of 32 European horses diagnosed with EMND completed a questionnaire regarding intrinsic, managemental, nutritional and environmental factors that could potentially be risk factors for EMND, and also regarding clinical signs, treatments and case outcome. Plasma/serum vitamin E data for these horses were supplied by the veterinarians. No control population was studied.

RESULTS

Thirteen of 32 horses (termed the 'grazing' group) had part- or full-time access to grass-based pasture at the onset of EMND (median duration at pasture 12 h/day, range 3-24 h). Five of these horses were at pasture for at least 235 h/day at the onset of EMND, 2 of which were at pasture for at least 23.5 h/day throughout the year. Despite grazing, all these horses had a low vitamin E status. The remaining 19 horses resembled those cases reported from North America, in that they had no or limited access to pasture.

CONCLUSIONS AND POTENTIAL RELEVANCE

A diagnosis of EMND should not be discounted on the basis that a horse has access, even full-time, to lush grass-based pasture. Inadequate vitamin E intake was probably not the sole cause of either the EMND or the low vitamin E status in the grazing horses; the latter was probably the result of abnormal bioavailability or excessive utilisation of vitamin E.

Lead Exposure as a Risk Factor for Amyotrophic Lateral Sclerosis

BACKGROUND

The etiology of amyotrophic lateral sclerosis (ALS) likely involves an environmental component. We qualitatively assessed literature on ALS and lead exposure. Problems of study design make case reports and studies of lead in blood or tissues difficult to interpret. Most previous case-control studies found an association of ALS with self-reported occupational exposure to lead, with increased risks of 2- to >4-fold. However, these results may have been affected by recall bias.

OBJECTIVE

To address inconsistencies among published reports, we used both lead biomarkers and interview data to assess lead exposure, and we evaluated the role of genetic susceptibility to lead.

METHODS

We conducted a case-control study in New England in 1993-1996 with 109 ALS cases and 256 population-based controls. We measured blood and bone lead levels, the latter using X-ray fluorescence, and interviewed participants regarding sources of lead exposure.

RESULTS

In our study, ALS was associated with self-reported occupational lead exposure, with a dose response for cumulative days of exposure. ALS was also associated with blood and bone lead levels, with a 1.9-fold increase in risk for each mug/dl increment in blood lead and a 2.3- to 3.6-fold increase for each doubling of bone lead. A polymorphism in the delta-aminolevulinic acid dehydratase gene was associated with a 1.9-fold increase in ALS risk.

CONCLUSION

These results, together with previous studies, suggest that lead exposure plays a role in the etiology of ALS. An increase in mobilization of lead from bone into blood may play a role in the acute onset of disease.

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.

Neurodegenerative diseases: an overview of environmental risk factors

The population of the United States is aging, and an ever-increasing number of Americans are afflicted with neurodegenerative diseases. Because the pathogenesis of many of these diseases remains unknown, we must consider that environmental factors may play a causal role. This review provides an overview of the epidemiologic evidence for environmental etiologies for neurodegenerative diseases such as Alzheimer disease, Parkinson disease, parkinsonian syndromes (multiple system atrophy and progressive supranuclear palsy), and amyotrophic lateral sclerosis. Epidemiologic evidence for an association between environmental agents' exposure and neurodegenerative diseases is not conclusive. However, there are indications that there may be causal links, and the need for more research is obvious.

Amyotrophic lateral sclerosis, rural environment and agricultural work in the Local Health District of Ferrara, Italy, in the years 1964–1998

Previous epidemiological surveys, both analytic and descriptive, in the Local Health District (LHD) of Ferrara, northern Italy, have indicated that rural residence and agricultural work might constitute risk factors for Amyotrophic Lateral Sclerosis (ALS). The present investigation is a demographic survey in the LHD of Ferrara in the years 1964-1998 which aimed to verify whether the level of urbanization and agricultural activities might influence the risk of ALS. Based on the data obtained in a recent incidence study in the LHD of Ferrara which reported a mean annual crude incidence rate of ALS in the years 1964-1998 of 1.63 per 100,000 population (95 % CI 1.31-2.00), it was possible to compare the number of observed ALS cases and the number of expected ALS cases according to the level of urbanization and usual occupation on the basis of the residential and occupational pattern identified in the population of the LHD of Ferrara in the study period under the assumption of a homogeneous distribution of ALS. The present survey identified four different levels of urbanization in the LHD of Ferrara in the study period and for none of them was a difference between the number of observed and expected ALS cases found. Also in the most rural of the four identified levels of urbanization (small villages with an average population in the study period lower than 1,000 inhabitants and scattered houses in the countryside) no difference was found between observed and expected number of ALS cases (observed ALS cases 16, 95% Poisson CI 9.1-25.9, expected ALS cases 18.3). Based on the occupational pattern identified in the population of the LHD of Ferrara in the study period the number of incident cases of ALS whose usual occupation was in agricultural work exceeded the expected number (observed ALS cases 22, 95% Poisson CI 13.8-32.3, expected ALS cases 6.0). The present findings indicate that rural residence itself does not influence the risk of ALS while agricultural activities could influence the risk of ALS, with occupational exposure to agricultural chemicals playing a possible role.

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: possible role of environmental influences

This treatise briefly discusses the genetic features of ALS and reviews environmental exposures in sporadic ALS. At least 10 genetic foci are responsible for cases of familial motor neuron disease and more are yet to be discovered. Research into sporadic ALS suggests that abundant factors apparently participate in the disease process. A singular cause and unifying disease and nerve dysfunction in polyneuropathies, a multitude of genetic, toxic, autoimmune, infectious, and systematic processes seem to be at play. The ALS syndrome likely will not be dissimilar.

Association of pesticide exposure with neurologic dysfunction and disease

Poisoning by acute high-level exposure to certain pesticides has well-known neurotoxic effects, but whether chronic exposure to moderate levels of pesticides is also neurotoxic is more controversial. Most studies of moderate pesticide exposure have found increased prevalence of neurologic symptoms and changes in neurobehavioral performance, reflecting cognitive and psychomotor dysfunction. There is less evidence that moderate exposure is related to deficits in sensory or motor function or peripheral nerve conduction, but fewer studies have considered these outcomes. It is possible that the most sensitive manifestation of pesticide neurotoxicity is a general malaise lacking in specificity and related to mild cognitive dysfunction, similar to that described for Gulf War syndrome. Most studies have focused on organophosphate insecticides, but some found neurotoxic effects from other pesticides, including fungicides, fumigants, and organochlorine and carbamate insecticides. Pesticide exposure may also be associated with increased risk of Parkinson disease; several classes of pesticides, including insecticides, herbicides, and fungicides, have been implicated. Studies of other neurodegenerative diseases are limited and inconclusive. Future studies will need to improve assessment of pesticide exposure in individuals and consider the role of genetic susceptibility. More studies of pesticides other than organophosphates are needed. Major unresolved issues include the relative importance of acute and chronic exposure, the effect of moderate exposure in the absence of poisoning, and the relationship of pesticide-related neurotoxicity to neurodegenerative disease.

Health Effects of Chronic Pesticide Exposure: Cancer and Neurotoxicity

Pesticides are widely used in agricultural and other settings, resulting in continuing human exposure. Epidemiologic studies indicate that, despite premarket animal testing, current exposures are associated with risks to human health. In this review, we describe the routes of pesticide exposures occurring today, and summarize and evaluate the epidemiologic studies of pesticide-related carcinogenicity and neurotoxicity in adults. Better understanding of the patterns of exposure, the underlying variability within the human population, and the links between the animal toxicology data and human health effects will improve the evaluation of the risks to human health posed by pesticides. Improving epidemiology studies and integrating this information with toxicology data will allow the human health risks of pesticide exposure to be more accurately judged by public health policy makers.

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.

Lead exposure and amyotrophic lateral sclerosis

BACKGROUND

Previous interview-based studies have suggested that exposure to neurotoxicants including metals might be related to ALS.

METHODS

We evaluated the relation of lead exposure to ALS, using both biological measures and interviews, in a case-control study conducted in New England from 1993 to 1996. Cases (N = 109) were recruited at two hospitals in Boston, MA. Population controls (N = 256) identified by random-digit dialing were frequency-matched to cases by age, sex, and region of residence within New England.

RESULTS

Risk of ALS was associated with self-reported occupational exposure to lead (odds ratio [OR] = 1.9; 95% confidence interval [CI] = 1.1-3.3), with a dose response for lifetime days of lead exposure. Blood and bone lead levels were measured in most cases (N = 107) and in a subset of controls (N = 41). Risk of ALS was associated with elevations in both blood and bone lead levels. ORs were 1.9 (95% CI = 1.4-2.6) for each microg/dl increase in blood lead, 3.6 (95% CI = 0.6-20.6) for each unit increase in log-transformed patella lead, and 2.3 (95% CI = 0.4-14.5) for each unit increase in log-transformed tibia lead.

CONCLUSIONS

These results are consistent with previous reports and suggest a potential role for lead exposure in the etiology of ALS.

Blood levels of toxic and essential metals in motor neuron disease

Toxic and essential metals have been implicated in the pathogenesis of sporadic motor neuron disease (SMND), but attempts to measure blood levels of these metals have led to contradictory results. We, therefore, measured blood levels of various metals using paired SMND/controls. In 20 subjects with SMND (15 males, five females, mean age 56.8 years) and 20 partner controls (15 females, five males, mean age 55.0 years) cadmium, lead, mercury, copper, zinc and selenium levels were measured in blood, plasma and red cells with inductively coupled plasma mass spectrometry and manganese levels with atomic absorption spectrophotometry. Results were analysed using non-parametric tests. Hypo-osmotic red blood cellfragility was estimated in six SMND/control pairs to see if hemolysis could account for increased metal levels. The plasma cadmium level was significantly raised in SMND cases (P = 0.005), but with considerable overlap between SMND and controls. No other metal levels were significantly different, though plasma lead in SMND had a tendency to be higher than controls. No difference in red cell fragility was found between groups. In conclusion, plasma levels of cadmium were raised in this SMND group, but the biological significance of this is uncertain. The measurement of metals in the blood of SMND cases seems unwarrranted for routine diagnostic testing.

Neurological deficits in solvent-exposed painters: a syndrome including impaired colour vision, cognitive defects, tremor and loss of vibration sensation

Five individuals are described who had participated in a study of former dockyard painters. All had worked between 16 years and 45 years as industrial painters, much of the time inside ships. All underwent structured neurological examination, colour vision testing (allowing calculation of a colour confusion index corrected for age and alcohol), and detailed psychometric testing. An occupational history sufficient to allow estimation of past exposure to solvents was taken. All gave a history of exposure to high concentrations of solvents at work, and several described episodes of acute narcosis. All showed neurological deficits and some had overt neurological disease, although in no case had this previously been linked to their work. The most striking features, sufficient to constitute a syndrome, were acquired blue-yellow colour vision deficits, coarse tremor, impaired vibration sensation in the legs and cognitive impairment. Their estimated cumulative exposures to solvents ranged between the equivalent of 13 and 37 calendar years working at the Occupational Exposure Standard concentration (OES years). This study for the first time gives an indication of the concentrations of solvents likely to lead to serious neurological disease in humans. It serves as a reminder to physicians to take an occupational history from patients with obscure neurological or psychological impairment.

Oxidative damage to nucleic acids in motor neurons containing mercury

Heavy metals have been implicated in the pathogenesis of sporadic motor neuron disease (MND). We were interested to see if inorganic mercury leads to oxidative damage in motor neurons since free radicals have been suspected to be involved in MND, so a method to examine oxidatively-damaged DNA in situ was used to examine individual motor neurons. Mice were exposed to 500 microg/m3 of mercury vapour for 2 h. Two, five, or ten days later sections from formalin-fixed, paraffin-embedded blocks of cervical spinal cord were incubated in avidin-FITC. Sections were examined under a fluorescence microscope and photographs of pairs of mercury-exposed and control spinal motor neurons were analysed semi-quantitatively for the amount of fluorescence using an image analysis program. Avidin fluorescence was seen in the perikaryon of both control and mercury-exposed motor neurons. In each control-mercury pair (four pairs per group) significantly more perikaryal fluorescence was seen in mercury-containing than in control motor neurons (Mann-Whitney testing). Mercury within the motor neuron perikaryon therefore leads to increased avidin binding, an indicator of oxidative damage to DNA. The findings support the hypothesis that an environmental toxin such as mercury can enter and damage motor neurons.

Monomelic amyotrophy following trauma and immobilization in children

Two children aged 9 and 11 years suffered from left elbow sprain and right anterior tibial tuberosity cortical fracture respectively and were treated with plaster cast immobilization for about 30 days. They regained normal strength afterwards, but 9 and 2 months later developed insidious progressive weakness and wasting in the affected limb, mainly evident in the musculature surrounding the site of injury and sparing hand and foot muscles. Two to three years later the condition stabilized. Sensory abnormalities were not found. Electromyographic examination showed neurogenic pattern confined to the impaired extremity. The focal quality and the unusual disposition of muscle involvement suggest a correlation between trauma and/or immobilization and monomelic amyotrophy.

Neurodegenerative diseases: occupational occurrence and potential risk factors, 1982 through 1991

OBJECTIVES

To identify potential occupational risk factors, this study examined the occupational occurrence of various neurodegenerative diseases.

METHODS

Death certificates from 27 states in the National Occupational Mortality Surveillance System were evaluated for 1982 to 1991. Proportionate mortality ratios were calculated by occupation for presenile dementia, Alzheimer's disease, Parkinson's disease, and motor neuron disease.

RESULTS

Excess mortality was observed for all four categories in the following occupational categories: teachers; medical personnel; machinists and machine operators; scientists; writers/designers/entertainers; and support and clerical workers. Clusters of three neurodegenerative diseases were also found in occupations involving pesticides, solvents, and electromagnetic fields and in legal, library, social, and religious work. Early death from motor neuron disease was found for firefighters, janitors, military personnel, teachers, excavation machine operators, and veterinarians, among others.

CONCLUSIONS

Neurodegenerative disease occurs more frequently in some occupations than in others, and this distribution, which may indicate occupational risk factors, should be further investigated.

Clinical epidemiology of amyotrophic lateral sclerosis

The introduction of palliative therapies in amyotrophic lateral sclerosis (ALS) will alter the epidemiology of ALS as it is known now. Although incidence rates will remain unchanged in the near future, prevalence rates will likely increase dramatically. Better understanding of the age-specific presentation of motor neuron diseases worldwide will shed light on the vexing questions concerning the variable incidence rates in some countries and apparent incidence gradients in North America and Europe.

Neurology

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