Multiple sclerosis in the Orkney and Shetland Islands. VI: The effects of migration and social structure.

Abstract

A number of studies have now shown a markedly higher prevalence of multiple sclerosis (MS) in northern Scotland.' The prevalence rates appear particularly high in the islands, with Orkney having the highest rate reported anywhere in the world.23Our specific task in this paper is to consider the possible effect of differential migration upon prevalence. The hypothesis is that part or all of the difference in prevalence may be the result of differences in migration, and the possibility that persons with MS are less likely to migrate, and that those who do are most likely to return after onset of the disease.Bradford Hill's4 pioneering study of the effect of migration on mortality rates produced the earliest clear evidence for our migration hypothesis. Additional and more recent evidence has come from those studies which have used height as an index of health status; most of these show that migrants are invariably taller than residents.5 The best British data are those collected by Martin,6 the Scottish Council for Research in Education,7 and Illsley, Finlayson, and Thompson.8 The latter are of particular interest because Aberdeen is the main destination for migrants from Orkney and Shetland. The authors demonstrated that migrants into the city were taller and had lower prematurity and perinatal death rates than Aberdeen women, and that the superiority was most marked among the more distant in-migrants.In the absence of studies of MS which provide a direct test of the migration hypothesis, this paper proceeds on the assumption that persons with MS migrate differently from the remaining section of the population. Assuming that those with MS are less likely to migrate, and that those who do are more likely to return, can we account for the observed prevalence rates? Before examining the special situations of Orkney and Shetland, we consider a number of factors which might plausibly affect prevalence rates.(1) FACTORS AFFECTING PREVALENCE RATES For heuristic purposes we postulate that the aetiology of MS is unaffected by geography, by climate, and by other environmental influences, but that rates are affected by geographic mobility and differential identification.Thus, variations in prevalence rates would arise in the following sets of circumstances:(i) Lower out-migration rates for MS cases

A health profile of adults with multiple sclerosis living in the community

“…Multiple sclerosis (MS) is estimated to affect more than 85,000 people in the United Kingdom, where it is more common than anywhere else in the world [1]. Current drug treatments have limited ability to modify the progression of MS, but much can be done to alleviate the symptoms and/or problems and disabilities associated with MS [2].…”

Genome-wide homozygosity and multiple sclerosis in Orkney and Shetland Islanders

“…Owing to the unusually high prevalence of MS in the Orkney and Shetland Islands, the Northern Isles of Scotland have long been of interest to MS researchers, and studies have ranged across the gamut of environmental and genetic risk factors. [9][10][11][12][13][14][15][16][17][18][19][20] Given the isolated location of these islands off the northern coast of Scotland, and consequently the relatively minimal movement in and out of the populations, several of these studies have examined the potential effects of inbreeding and consanguinity within these populations as a means of indirectly assessing the role of recessive genetic effects in MS. 9,11,12 Using pedigree data for MS cases and controls in Orkney, Roberts 9 found 13% in each group to be the product of consanguineous unions. However, the inbreeding coefficients (the probability that two alleles at a random locus are identical-by-descent, having been inherited from a common ancestor) were twice as high in cases (F¼0.00364) as in controls (F¼0.00170).…”

FutureMS cohort profile: a Scottish multicentre inception cohort study of relapsing-remitting multiple sclerosis

“…Scotland has long been known to have a high incidence of MS 49. The reasons for this remain unknown despite long-running speculation 17 50–62. The Scottish northern isles for many decades have been recognised as particularly burdened 63.…”