The worldwide prevalence of multiple sclerosis
Introduction
Despite the wealth of epidemiological data deriving from the systematic studies of multiple sclerosis (MS) that have been carried out for over 70 years, any attempt at redefining the pattern of MS geographic distribution is still a difficult task. In fact, comparing prevalence studies of different areas and at different times implies a number of problems: (a) the variability of the surveyed populations in terms of size, age structure, ethnic origin and composition [1]; (b) the difference when determining the numerator, i.e. the recognition of benign and very early cases [2]; (c) the extent to which complete case ascertainment is achieved based on geographic and time variables, access to medical care, local medical expertise, number of neurologists, availability of and accessibility to new diagnostic procedures, degree of public awareness about MS, and on the investigators’ zeal and resources [2], [3]; (d) the use of different diagnostic criteria and the interobserver variability when applying them [1]. A description of MS geography worldwide is tentatively presented (for detailed references, see review by Rosati [4]).
Section snippets
Europe
The prevalence rates estimated for Scotland and its offshore islands over the last 25 years range from 145 to 193 per 100 000 and are the highest so far detected anywhere in the world for large populations. In England and Wales, prevalence rates have varied from 74 to 112 in the last 15 years; 66 per 100 000 was the rate yielded by a nationwide survey in the Republic of Ireland in 1971, whereas a prevalence of 168 was estimated in northern Ireland. The highest frequencies of MS in the UK and
The Americas
The studies carried out in Canada in the years before 1990 showed a prevalence of MS averaging around 90 per 100 000. From east to west, the rates were 55 for Newfoundland in 1984, 68 for Ottawa in 1975, 94 for London, Ontario in 1984, 111 for Saskatoon, Saskatchewan in 1977, 87 for Cardston, Alberta in 1988, and 91 for British Columbia in 1982, indicating an east-to-west gradient of frequency from a possible higher density of French-speaking people in the East and Newfoundland, as compared to
Asia
The risk of MS in Asiatic Russia has long been estimated to be low. In Siberia, however, following a major migration of Russians eastward, along with large-scale industrialization and a marked increase of the resident population, the frequency of MS has gradually increased. Most of the recent data on MS prevalence in Siberia indicate prevalence rates ranging from 12 to 41 per 100 000 in a population of mostly Russian ancestry. MS was found to be very rare among the native Siberian peoples and
Africa and the middle east
Data from the Middle East also emphasize the importance of the genetic-historical factor in driving the distribution of MS. MS prevalence among Arabs was reported to be between 4 and 8. In Kuwait, with a population of nearly two million of whom about 75% were Arabs, the overall MS prevalence rate in 1988 was 10 per 100 000. The rate in the Arab patients, the vast majority of whom were Kuwaitis, Palestinians and Egyptians, was 13, whereas among non-Arabs, 95% of whom were southeastern Asians,
Australasia
In the early 1980s MS surveys were conducted in nine separate regions of Australia and New Zealand, reporting prevalence rates varying from 11 in North Queensland, Australia to 69 in Otago-Southland, New Zealand, based on definite and probable MS. The geographic distribution indicated a south-to-north gradient, interpretable as correlating with a gradient of environmental factors. In New Zealand, such a gradient was more appreciable, but the differences were thought to reflect the higher impact
Discussion
A critical examination of the more recent data on MS prevalence leads to the appreciation of a greater impact of genetic factors on the acquisition of the disease. The rarity of MS in Samis, Turkmen, Uzbeks, Kazakhs, Kirgizis, native Siberians, North and South Amerindians, Canadian Hutterites, Chinese, Japanese, African blacks and New Zealand Maoris and its high risk in Sardinians, Parsis and Palestinians, as well as in South African English-speaking whites as compared to Afrikaners, point to
Acknowledgements
Special thanks to Mr Corrado Occhineri for his technical support. This project received support from the Istituto Superiore di Sanità, Fondazione Italiana Sclerosi Multipla (Grant #R/69/97), the Ministero dell'Università e della Ricerca Scientifica e Tecnologica, and Regione Autonoma della Sardegna.
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