Reappraisal of possible etiologic factors in multiple sclerosis.

Abstract

IN 1961 a nationwide survey of multiple I sclerosis (MS) in Israel was completed and all patients living in the country on January 1, 1960, were identified.1 The study was designed to obtain information on the frequency of the disease in groups of diverse national origin. Israel was particularly suited for such a study because its population included immigrants from every continent and many different countries. Moreover, the quality of medical care throughout the country was of a high standard. All segments of the population had ready access to the medical facilities and disease did not bar an immigrant from entering the country. Prevalence rates of multiple sclerosis for groups of different countries of origin were calculated and the rates showed wide differences. The distribution of rates showed a gradient of decreasing prevalence toward the equator. Multiple sclerosis was about six times more common among immigrants born in Europe than among immigrants from Afro-Asian countries and native-born Israelis.2 In 1963, an epidemiologic study was conducted in which the patients with multiple sclerosis identified in the survey were compared to matched controls with respect to a large number of factors of possible relevance to the etiology of the disease. It was postulated that the patients would report a different experience than controls with factors of etiologic importance. Furthermore, the availability in Israel of groups with different prevalence rates was expected to enhance opportunities for detecting a gradient in exposure to etiologic factors which might not be apparent if patients and controls were compared in a population of uniform origin. Several factors examined in that study revealed significant differences between patients and controls.3Y5 The present study was designed to explore these factors in greater detail.