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An increasing incidence and prevalence of multiple sclerosis (MS) has become apparent in most recent studies in both the Northern and Southern hemispheres. Reports of cross-sectional analyses from several countries have demonstrated an increasing female-to-male sex ratio, suggesting that the increase in frequency is predominantly in females. An earlier Canadian study in large pedigrees also found an increased risk for MS in later-born female children. To investigate further the increased frequency of MS in females, the Canadian Collaborative Study Group conducted a longitudinal study of a cohort of 27,074 MS patients born from 1931 to 1980.
The female-to-male sex ratio of people with MS progressively and significantly increased during the st…