A PILOT STUDY OF THE RELATIONSHIP BETWEENMULTIPLE SCLEROSIS AND THE PHYSICAL ENVIRONMENT

IN NORTHWEST IRELAND

MARGARET GILMORE and EAMONN GRENNANInstitute of Technology, Ballinode, Sligo, Ireland

Received 25 June 2001; accepted in revised form 10 November 2001

Abstract. Multiple sclerosis (MS) is a neurological disease of unknown origin, but it is thoughtlikely to have an environmental component in addition to genetic predisposition. It appears commonin areas with underlying radon-producing granites. Radon exposure before the age of 15 years is pos-tulated as a contributory cause in genetically susceptible individuals. Pilot studies were undertaken,with results which indicate that radon exposure may be a factor, and that the hypothesis warrantsfurther investigation.

Key words: environmental factors, geology, multiple sclerosis, Northwest Ireland, prevalence,radioactivity

1. Introduction

Multiple sclerosis (MS) is a chronic neurological condition, with onset mainly inyoung adults. The cause is unknown, but thought to be multifactorial. It is gener-ally accepted that the discovery of some triggering mechanism will play a role indiscovering a cause. Commonly noted associations in the literature include

• Age of onset is typically between 15 and 50 years (Edwards et al., 1995).• Gender: Women are affected more than men in ratio about 1.7:1 (Burnfield,

1991).• Genetics: A monozygotic twin has a higher risk (25%), and siblings have

above average risk (3%) while overall prevalence in those studies is 100/105

(Compston et al., 1998). There is as yet no known genetic signature. Geneticpredisposition may increase susceptibility but this does not provide a completeexplanation, and it seems likely therefore that MS may be environmentallyinduced in those with a genetic predisposition.

• Ethnicity: The low incidence of MS amongst Eskimos, Bantus and AmericanIndians has been used to dismiss the importance of the environment, prefer-ring to attribute it more to their genetic inheritance than some accident ofgeographical location (Benz, 1988). However, all of these ethnic exceptionslive predominantly outdoor, nomadic lives often over areas of very old (plus2000 million years) cratonic rocks. Also it is acknowledged that ‘whites aremore than twice as likely as other races to develop MS’ (NINDS, 1996). The

Environmental Geochemistry and Health 25: 157–163, 2003.© 2003 Kluwer Academic Publishers. Printed in the Netherlands.

158 MARGARET GILMORE AND EAMONN GRENNAN

present position clarifying the importance of place versus race is very wellsummarised by Edwards et al. (1995) in stating “Migration before the ageof 15 between areas of contrasting prevalence affects the risk of developingthe disorder, and children born in Britain of immigrants from areas of lowprevalence have the same risk of developing the condition as the indigenouspopulation”, and it is supported by Barker et al. (1998), who quote the statisticthat UK migrants to South Africa have a prevalence rate for MS of 40/105,whereas the children born in South Africa of UK parents have a prevalencerate of only 7/105.

• Environmental agent: It is accepted by most authorities that exposure to someenvironmental agent ‘during a critical period in childhood’, that is before theage of 15 years, appears to be a factor in the subsequent development of MS ingenetically susceptible individuals (Compston et al., 1998). Attempts to im-plicate viruses while exhaustive have proved inconclusive (Mogensen, 1997).

• Geography: People in temperate latitudes have a fivefold higher incidenceof MS than in tropical regions (NINDS, 1996). This is true on a worldwidescale, despite the fact that these areas have large variations in temperatures,lifestyles and built environments. MS is more prevalent in Europe, NorthAmerica and Australia. These countries, while broadly within the temperatezones, have very wide differences in natural and built environment. However,these areas are underlain by rocks of the same age (300–550 million yearsago) and similar in mineral composition, structure, and fossil content, havebeen contiguous prior to the development of the proto-Atlantic ocean about250 million years ago (Chernicoff et al., 1997). In addition, there are wideregional variations, for example in UK – “The gradient in prevalence (canbe) seen between southern England (63/105), northern England and northernIreland (76–79/105), Wales (ca. 113/105), northeast Scotland (155/105) andthe Orkneys (258/105)” Swingler and Compston (1986, p. 1115). The south-west of England has the highest level of radon in household air in the UK(Appleton and Ball, 1995), and yet a lower prevalence of MS than in Scotland,but it may be argued that different population migration patterns apply, forexample a higher number of retired people choosing to live in the southwest.Numerous other studies have documented significant gradients within areasof high prevalence, for example in France, Kurtzke and Delasnerie-Laupretre(1996) noted the clustering of high frequency regions in the northeast com-pared with the south and west, and Rosati et al. (1996) noted that northwesternSardinia shows twice the prevalence of MS compared to continental Italy.

2. Background to studies undertaken

The northwest of Ireland (where the authors work) appears to have one of thehighest prevalence rates of MS in Ireland though there is as yet no reliable national

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database. The area is one of the highest radon-emitting areas in Ireland, withDonegal, in particular, containing some of the most highly uranium enriched gran-ites in the country. This provided the motivation for the pilot study that was under-taken, that is an attempt to refine the well-known geographical association betweenMS and temperate climates to a more coherent association between MS andgeology.

— The role of geology for some diseases is well established, for example silicosisand coal mining; asbestosis and exposure to asbestos in mining or processing;lung cancer and exposure to radon; malignant mesothelioma associated withpresence of erionites in central Turkey (Temel and Gundogdu, 1995) and selen-ium toxicity leading to skin and nervous system disorders (Fordyce et al.,2000). The work of Bolviken et al. (1997) in Norway has noted an associationof radon enriched granites and the prevalence of MS.

— In the case of MS, the hypothesis is posed that a geological factor, for ex-ample radon exposure may provide a trigger in susceptible individuals, whoare exposed to it before the age of 15 years.

— Radon gas is generated in the earth’s crust by the radioactive decay of uraniumwithin, for example granites many kilometres below the surface. Radon maybecome trapped within buildings; it is nine times heavier than air and thereforeis more concentrated at ground levels. It follows logically that bedrooms atground floor level give a greater exposure, as would floor play by children.Radon has an accepted association with lung cancer, and it is also known tobe soluble in fat. The myelin tissue affected around the nerves in MS is fattytissue.

3. Methods

3.1. STUDY 1

Examined membership of the MS Society in Ireland, which broadly correlates withareas of suspected higher prevalence, that is a band of lower prevalence acrosscentral Ireland in a southwest to northeast direction, with higher prevalence inthe remainder of the country, consistent with the general pattern of greater radonemissions as evident on surveys to date by Radiological Protection Institute ofIreland.

3.2. STUDY 2

A questionnaire survey was administered with the assistance of the Northwest MSTherapy Centre. Its validity was assured by similarity with studies already citedin male/female ratio and the reported rate of prevalence of MS in relatives ofrespondents. The sample was small (67 respondents, response rate 33%) but results

160 MARGARET GILMORE AND EAMONN GRENNAN

TABLE I

Summary of results

Sample (%) Control

House type

Single storey 67.20 Not available

Two storey 22.30 Not available

Other 5.90 Not available

Unknown 4.60 Not available

House age

Pre-1920 71.40 44.70% (CSO, 1981)

1920–1960 23.80 38.32%

1960 and later 4.76 15.47%

Water

Public/group scheme 30.42 75.58% (CSO, 1981)

Private (well) 61.01 16.56%

Unknown 8.47 7.40%

Sanitation

Flush 35.48 69.98% (CSO, 1971)

Dry 37.00 10.10%

None 27.41 19.86%

Heating

Open fire 85.24 32.40% (CSO, 1981)

Central heating 4.90 39.54%

Other heating system 9.70 28.06%

are interesting. Questions were asked concerning house age, number of storeys inthe building, type of heating, sanitation and source of water supply, in relation torespondents’ childhood homes, that is before the age of 15 years (Table I).

4. Results

Where possible, data was compared with similar data from the Central Statis-tics Office (CSO, 1971, 1981). Briefly, respondents (all of whom had MS) weremore likely to live in one storey, older houses, with private water supply (springwell), with less houses having modern sanitation and more houses using openfires for heating. Most respondents were still living in their childhood home orlocality.

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5. Discussion

5.1. STUDY 1

On commencing research, the lack of national statistics for the prevalence of MSbecame evident. Since the hypothesis was in the early stages of development, itwas decided to investigate the broad relationship between membership of the MSSociety of Ireland and radon levels. This was examined by noting the countyareas of membership of this Society, and relating these figures to documentedradon levels. There was a good correlation between counties with low radon levelsand low membership of the Society, that is in an area running in a southwest tonortheast direction from North Kerry through the mid-west and the midlands toMeath.

However, because the hypothesis is area specific (maximum 100 km2), and be-cause the only part of the address which we requested (for confidentiality reasons)was the county (minimum 1000 km2), this turned out to be too broad for a positivecorrelation between counties which had both high radon levels and a high member-ship of the Society, because some of these counties had both high and low radonareas.

One of the difficulties encountered in this research has been the dearth of in-formation on this avenue of study. However, one of the reviewers has pointed outthat Neilson et al. (1996) found ‘weaker, but statistically significant, associationswere observed between indoor radon gas concentrations, terrestrial gamma radi-ation and marginal variations in Motor Neuron Disease mortality’. (Motor neurondisease and MS have some common features.) The authors go on to state, ‘fur-ther research is required to investigate this association’. This paper will help tocontribute to that research.

Swingler and Compston (1986) highlighted 11 areas in Great Britain whichhave prevalence levels in excess of 56/105. Appleton and Ball (1995) published anatural radioactivity map of Great Britain. Many of the 11 areas in Swingler andCompston are co-incident with the areas of high radioactivity. These include theOrkneys, Aberdeenshire, Isle of Skye, the South Pennines, Devon and Cornwall.Whilst the prevalence of MS in the southwest is significantly lower than that inScotland, it can be argued that the former is also chosen frequently as a retirementarea and thus has a much lower indigenous cradle to grave population. This is oneof the complications that remain to be explored.

5.2. STUDY 2

The relevance of living, playing and sleeping in one-storey houses has already beenmentioned in the context of exposure to radon. Children spend much of their timeindoor, playing and sleeping, and therefore may be particularly vulnerable. Houseage was generally old and therefore the houses would be less likely to have radon-lessening work undertaken; however it was not possible in the present study to

162 MARGARET GILMORE AND EAMONN GRENNAN

check the actual levels of radon. Water supply was more commonly from privatesources, which are interpreted as spring wells, used for supply of individual house-holds. Again it would be interesting to be able to analyse this water. Sanitationwas queried, as one theory for causation of MS is that modern sanitation causes adecrease in exposure to micro-organisms and therefore lessened immunity. Thecohort in the study, with less modern sanitation, should therefore have greaterimmunity in general, thus weakening an argument for an infective agent. Thereis a marked predominance in the use of open fires, compared with national figures.The heating source question did not ask for type of fuel; however if peat is thepredominant type, this may point to an increase in release of radon from this sourceinto the house. No questions on diet were included in this pilot survey.

6. Conclusions

This was a small pilot survey with retrospective gathering of data and no actualmeasurement of radon levels in the houses in question. However, the preliminaryresults suggest a further more detailed and scientific study is warranted. Is there anenvironmental factor such as higher radon exposure in the early years of life, whichincreases the genetic susceptibility of individuals developing MS? If the hypothesisis proven, then it would be imperative to try to prevent further cases by equip-ping homes and other buildings, especially schools, with anti-radon strategies. Thefinancial and human cost savings would be immeasurable.

Acknowledgements

The assistance of the Northwestern Health Board, the MS Society of Ireland andthe Northwest MS Therapy Centre are gratefully acknowledged.

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