THE EPIDEMIOLOGY OF MULTIPLE-SCLEROSIS

Although the cause of multiple sclerosis (MS) is unknown, epidemiologi c studies support both genetic and environmental components of suscept ibility, Reports of clusters, small ''epidemics,'' geographic variatio n in prevalence, and alteration of MS susceptibility by migration supp ort an environmental factor (or factors); The higher risk for MS in Eu ropeans and in relatives of patients and the existence of MS-resistant ethnic groups support genetic predisposition, Findings from epidemiol ogic studies are most consistent with an environmental influence occur ring on a background of genetic susceptibility as the cause of MS, Cur rently, there is little evidence for a single or unique environmental cause of MS.