Effect of birthplace on the development of amyotrophic lateral sclerosis and multiple sclerosis. A study among Finnish war evacuees

Changes in multiple sclerosis epidemiology in Finland over five decades

Finland is a high-risk region for multiple sclerosis (MS) with several epidemiological studies on the subject published since 1964, but these have not been comprehensively scrutinized. The objective of this study was to review previous studies of Finnish MS epidemiology, introduce new data on MS prevalence in western parts of Finland and do further analyses on data from previous studies. We performed a systematic search on articles regarding MS epidemiology in Finland in PubMed database, and all relevant articles were included in this review. MS prevalences in the western hospital districts of Vaasa, South Ostrobothnia and Pirkanmaa were calculated in 1980-2007 by using previously unpublished data obtained from a retrospective search from hospital administrative registries. To enhance comparability of the epidemiological figures, we calculated age-standardized prevalence of MS from the new data from western hospital districts and previous data from North Ostrobothnia, Southwest Finland and North Karelia. Marked regional differences in MS epidemiology were confirmed with concentration of the disease in the western and south-western parts of the country. The highest regional age-standardized MS prevalence of 288/100 000 was reported in South Ostrobothnia in 2007. A clear and stable increase in MS prevalence was observed through the decades, but the only marked increase in incidence happened in 1990s. Methodological differences hampered direct comparisons of different studies, highlighting the importance of common principles of reporting and standardizing the epidemiological figures. More comprehensive studies on MS epidemiology are still warranted to yield important information concerning the aetiology of the disease.

Hypothesis: Etiologic and Molecular Mechanistic Leads for Sporadic Neurodegenerative Diseases Based on Experience With Western Pacific ALS/PDC

Seventy years of research on Western Pacific amyotrophic lateral sclerosis and Parkinsonism-dementia Complex (ALS/PDC) have provided invaluable data on the etiology, molecular pathogenesis and latency of this disappearing, largely environmental neurodegenerative disease. ALS/PDC is linked to genotoxic chemicals (notably methylazoxymethanol, MAM) derived from seed of the cycad plant (Cycas spp.) that were used as a traditional food and/or medicine in all three disease-affected Western Pacific populations. MAM, nitrosamines and hydrazines generate methyl free radicals that damage DNA (in the form of O⁶-methylguanine lesions) that can induce mutations in cycling cells and degenerative changes in post-mitotic cells, notably neurons. This paper explores exposures to naturally occurring and manmade sources of nitrosamines and hydrazines in association with sporadic forms of ALS (with or without frontotemporal degeneration), progressive supranuclear palsy, and Alzheimer disease. Research approaches are suggested to examine whether these associations might have etiological significance.

Spatial analyses of ALS incidence in Denmark over three decades

OBJECTIVE

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease of the motor neuron with very few known risk factors. We conducted a spatial epidemiologic analysis of ALS incidence in Denmark to assess the contribution of sociodemographic determinants to geographic variation.

METHODS

We analyzed 4249 ALS cases (1982-2013), each with 100 controls matched on sex and birth year. Odds ratio and 95% confidence bands at birth and diagnosis/index locations were calculated using generalized additive models. We included a bivariate spatial smooth for location in our conditional logistic regression adjusted for socioeconomic status and marital status. We also conducted analyses adjusted for both birth and diagnosis addresses to separate location effects.

RESULTS

We observed significantly elevated ALS odds near Copenhagen for both the birth and diagnosis period analyses. Sociodemographic factors did not explain the observed patterns. When we further adjusted our spatial analyses by including both birth and diagnosis addresses, the significant area of elevated male ALS odds by birth address shifted to northwest Denmark away from Copenhagen, and there was little evidence of variation among women. Geographic variation at diagnosis differed between male and females, suggesting that patterns are not just due to regional variation in case ascertainment.

CONCLUSION

ALS incidence in Denmark is associated with both location at birth and diagnosis, suggesting that geographic variation may be due to exposures occurring at birth or closer to diagnosis, although the latter could relate to case ascertainment issues.

Modelling exposure opportunities: estimating relative risk for motor neurone disease in Finland

This paper addresses the issues surrounding an individual's exposure to potential environmental risk factors, which can be implicated in the aetiology of a disease. We hope to further elucidate the 'lag' or latency period between the initial exposure to potential pathogens and the physical emergence of the disease, with specific reference to the rare neurological condition, motor neurone disease (MND), using a dataset obtained from the Finnish Death Certificate registry, for MND deaths between the period 1985-1995. A space-time approach is adopted, whereby patterns in both time and space are considered. No prior assumptions about the aetiology of MND are adopted. By using methods for the analysis of point processes, which preserve the continuous nature of the data, we resolve some of the problems of analysis that are often based on arbitrary areal units, such as postcode boundaries, or political boundaries. We use kernel estimation to model space-time patterns. Raised relative risk is assessed by adopting appropriate adjustments for the underlying population at risk, with the use of controls. Significance of the results is assessed using Monte Carlo simulation, and comparisons are made with results obtained from Openshaw's geographical analysis machine (GAM). Our results demonstrate the utility of kernel estimation as a visualisation tool. Small areas of elevated risk are identified, which need to be more closely examined before any firm conclusions can be drawn. We highlight a number of issues concerning the inadequacies of the data, and possibly of the techniques themselves.

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.

Adult onset motor neuron disease: worldwide mortality, incidence and distribution since 1950

This review examines the commonly held premise that, apart from the Western Pacific forms, motor neuron disease (MND), has a uniform worldwide distribution in space and time; the methodological problems in studies of MND incidence; and directions for future epidemiological research. MND is more common in men at all ages. Age-specific incidence rises steeply into the seventh decade but the incidence in the very elderly is uncertain. A rise in mortality from MND over recent decades has been demonstrated wherever this has been examined and may be real rather than due to improved case ascertainment. Comparison of incidence studies in different places is complicated by non-standardised methods of case ascertainment and diagnosis but there appear to be differences between well studied populations. In developed countries in the northern hemisphere there is a weak positive correlation between standardised, age-specific incidence and distance from the equator. There is now strong evidence for an environmental factor as the cause of the Western Pacific forms of MND. A number of clusters of sporadic MND have been reported from developed countries, but no single agent identified as responsible.

Evidence for clustering of amyotrophic lateral sclerosis in Wisconsin

Clustering of amyotrophic lateral sclerosis (ALS) occurs in the western Pacific, but has not been convincingly demonstrated for the sporadic form of the disease which occurs throughout the rest of the world. Using death certificate data we identified 529 ALS-associated deaths in Wisconsin during the interval 1973-82, representing a statewide mortality rate of 1.12 deaths/100,000/yr. Using computer simulation we show that cases were not homogeneously distributed throughout the population and that there exists a significant cluster of cases in northeastern Wisconsin.

Amyotrophic lateral sclerosis in Middle-Finland: an epidemiological study

Amyotrophic lateral sclerosis (ALS) was diagnosed in 36 patients in Middle-Finland Central Hospital District during 1976-1981. The annual incidence of ALS was 2.4 per 100,000 population and the prevalence rate was 6.4 per 100,000 population. The age-specific incidences of ALS were similar for men and women with a maximum of 14/100,000/year in the age group 60-69 years. The initial symptoms originated in 37% of the patients from bulbar and in 63% from spinal levels. Bulbar onset was more common in patients aged 60 years or more compared with younger patients. Patients with bulbar onset had a significantly poorer prognosis than those with spinal onset, which explained the poorer prognosis of older patients. 4 matched controls were chosen for each ALS patient from the files of the Central Hospital. There was no difference between the patients and the controls with respect to previous injuries, surgical operations, malignant neoplasms, or exposure to domestic animals. An earlier observation that evacuees from Karelia ceded to USSR after World War II should have a prevalence twice that of the remaining population was not substantiated.

Amyotrophic lateral sclerosis in Finland: birthplaces of patients, parents and grandparents

Amyotrophic lateral sclerosis (ALS) appears to be more prevalent in the southeastern part of Finland and among the war evacuees displaced from this area after the World War II than elsewhere in the country. A random sample of 31 ALS patients was chosen and the birthplaces of their ancestors traced back in two generations to find out whether there would be any tendency of clustering in certain regions of the country. No such trend was found. This finding speaks against a genetically determined tendency for the disease.