An exploratory spatial analysis of ALS incidence in Ireland over 17.5 years (1995-July 2013).

James Rooney,Alice Vajda,Katy Tobin,Mark Heverin,Arlene Crampsie,Orla Hardiman,Susan Byrne,Anthony Staines,Weidong Le

doi:10.1371/journal.pone.0096556

James Rooney, Alice Vajda + Show 7 more

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https://doi.org/10.1371/journal.pone.0096556

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Abstract

IntroductionThere has been much interest in spatial analysis of ALS to identify potential environmental or genetically caused clusters of disease. Results to date have been inconclusive. The Irish ALS register has been recently geocoded, presenting opportunity to perform a spatial analysis on national prospectively gathered data of incident cases over an 18-year period.Methods1,645 cases of ALS in Ireland from January 1995 to July 2013 were identified from the Irish ALS register. 1,638 cases were successfully geocoded. Census data from four censuses: 1996, 2002, 2006 & 2011 were used to calculate an average population for the period and standardized incidence rates (SIRs) were calculated for 3,355 areas (Electoral Divisions). Bayesian conditional auto-regression was applied to produce smoothed relative risks (RR). These were then mapped for all cases, males & females separately, and those under 55 vs over 55 at diagnosis. Bayesian and linear regression were used to examine the relationship between population density and RR.ResultsSmoothed maps revealed no overall geographical pattern to ALS incidence in Ireland, although several areas of localized increased risk were identified. Stratified maps also suggested localized areas of increased RR, while dual analysis of the relationship between population density and RR of ALS yielded conflicting results, linear regression revealed a weak relationship.DiscussionIn contrast to some previous studies our analysis did not reveal any large-scale geographic patterns of incidence, yet localized areas of moderately high risk were found in both urban and rural areas. Stratified maps by age revealed a larger number of cases in younger people in the area of County Cork - possibly of genetic cause. Bayesian auto-regression of population density failed to find a significant association with risk, however weighted linear regression of post Bayesian smoothed Risk revealed an association between population density and increased ALS risk.

Highlights

There has been much interest in spatial analysis of Amyotrophic Lateral Sclerosis (ALS) to identify potential environmental or genetically caused clusters of disease
To the best of our knowledge, this is the first areal mapping of ALS incidence based upon a national prospective population based ALS register
Areas of moderately higher risk appear in North Dublin, Louth & Meath, Cork, the Dingle peninsula in Kerry, and the area on the south-west coast of Donegal

Summary

Introduction

There has been much interest in spatial analysis of ALS to identify potential environmental or genetically caused clusters of disease. Amyotrophic Lateral Sclerosis (ALS) is a terminal neurodegenerative condition of complex genetic origin, with an annual incidence in Ireland of approximately 2.6 per 100,000 and a lifetime risk of 1:300[1]. As ALS is a disease that manifests later in life, genetic factors present at birth are likely to interact with later-life environmental factors. Observations from Guam[4] and the Kii peninsula of Japan[5,6] of localised higher incidence rates of ALS generated interest in possible environmental causes, leading to interest in the spatial analysis of ALS incidence[7,8,9,10]. The methods of spatial analysis have evolved along with advances in technology, the development of new statistical approaches and with the emergence of geospatial information systems (GIS)[11]

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