Epidemiology and Estimated Population Burden of Selected Autoimmune Diseases in the United States

Summary The uneven distribution of multiple sclerosis (MS) across populations can be attributed to differences in genes and the environment and their interaction. Prevalence and incidence surveys could be affected by inaccuracy of diagnosis and ascertainment, and prevalence also depends on survival. These sources of error might play a part in the geographical and temporal variations. Our literature search and meta-regression analyses indicated an almost universal increase in prevalence and incidence of MS over time; they challenge the well accepted theory of a latitudinal gradient of incidence of MS in Europe and North America, while this gradient is still apparent for Australia and New Zealand; and suggest a general, although not ubiquitous, increase in incidence of MS in females. The latter observation should prompt epidemiological studies to focus on changes in lifestyle in females. New insights into gene–environment and gene–gene interactions complicate interpretations of demographic epidemiology and have made obsolete the idea of simple causative associations between genes or the environment and MS.

The Changing Demographic Pattern of Multiple Sclerosis Epidemiology

The systematic study of multiple sclerosis (MS) in populations, started in 1929 by Sydney Allison, now consists of over 400 publications dealing with the prevalence of MS throughout the world. However, any attempt to redefine the pattern of geographical differences in MS frequency remains as difficult as ever. The comparison of prevalence studies carried out in different areas and times is made difficult by the variability in surveyed population sizes, age structures, ethnic origins and composition, and the difficult quantification of numerators, especially regarding the recognition of benign and very early cases. Additionally, complete case ascertainment depends on access to medical care, local medical expertise, number of neurologists, accessibility and availability of new diagnostic procedures, the degree of public awareness about MS, and the investigators' zeal and resources. Critical examination of the more recent data on MS prevalence leads to some revisions of previously held concepts, the most interesting of which is the appreciation of the greater influence of genetic factors on disease acquisition. The rarity of MS among Samis, Turkmen, Uzbeks, Kazakhs, Kyrgyzis, native Siberians, North and South Amerindians, Chinese, Japanese, African blacks and New Zealand Maoris, as well as the high risk among Sardinians, Parsis and Palestinians, clearly indicate that the different susceptibilities of distinct racial and ethnic groups are an important determinant of the uneven geographic distribution of the disease. The updated distribution of MS in Europe, showing many exceptions to the previously described north-south gradient, requires more explanation than simply a prevalence-latitude relationship. Prevalence data imply that racial and ethnic differences are important in influencing the worldwide distribution of MS and that its geography must be interpreted in terms of the probable discontinuous distribution of genetic susceptibility alleles, which can however be modified by environment. Because the environmental and genetic determinants of geographic gradients are by no means mutually exclusive, the race versus place controversy is, to some extent, a useless and sterile debate.

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The prevalence of multiple sclerosis in the world: an update.

OBJECTIVES Previous studies have shown that multiple sclerosis is very uncommon among Indian and Pakistani immigrants to England but that their children born in the United Kingdom, in the age groups available for study, have a similar risk of developing the disease as occurs in the general British population. The present study was to ascertain if these immigrants who enter England as children below the age of 15, have a higher risk of developing multiple sclerosis than those that enter after this age. METHODS A search was made in Greater London, the West Midlands, Leicester, Bradford, Halifax, and Huddersfield to find ethnic Indian, Pakistani, and Bangladeshi immigrants to England with multiple sclerosis. During the course of the study some immigrants from the Caribbean with multiple sclerosis were also found. The population at risk by ethnic group and age at entry was not available from the 1991 Census but was available in the annual Labour Force Surveys. RESULTS Indian and Pakistani immigrants who entered England younger than 15 had a higher risk of developing multiple sclerosis than those that entered after this age. Caribbean immigrants, who have a higher multiple sclerosis prevalence than Asian immigrants, did not show this difference. CONCLUSION This study confirms previous studies which show that the environment during childhood is a major factor in determining the risk of developing multiple sclerosis.

https://jnnp.bmj.com/content/jnnp/63/5/565.full.pdf

Age at immigration to England of Asian and Caribbean immigrants and the risk of developing multiple sclerosis

Epidemiology of Multiple Sclerosis

We carried out a door-to-door-survey to screen a community of 14,010 people (Parsis living in colonies in Bombay, India) for possible neurologic diseases, and used defined diagnostic criteria to evaluate people who tested positive on the screening survey. There were three clinically definite cases of multiple sclerosis (21/100,000). This is the first prevalence survey for multiple sclerosis in a large developing country.

N. H. Wadia

Papers

Prevalence of multiple sclerosis in the Parsis of Bombay