BACKGROUND: Newfoundland and Labrador, Canada, have been almost exclusively populated by immigrants from southwest England and southeast Ireland. The province's population grew largely by natural increase from 20,000 people in 1835 to half a million at present. Very little interregional migration occurred within the province. This uniquely-populated region and its subsequent founder effect provide the basis to develop models of disease prevalence. OBJECTIVES: To develop a model for the regional prevalence of multiple sclerosis (MS), accounting for settlement patterns and geographic location (latitude). METHODS: All living MS patients with confirmed addresses (438 patients) in the province were mailed a survey requesting their place of birth. Regional prevalences were calculated from a 75% rate of return of the survey. Theoretical regional prevalences were proportionally calculated from the source prevalences of southwest England, southeast Ireland, Scotland and the Channel Islands based on settlement patterns. These theoretical regional prevalences were corrected for geographical variations of latitude based on observations in the United Kingdom. Theoretical and actual regional prevalences were compared. RESULTS: When actual regional prevalences were compared with theoretical prevalences, very little variation was noted, especially after correcting for variation in latitude. CONCLUSION: A regional variation in MS prevalence is noted in the island portion of Newfoundland and Labrador. This regional variation can be modeled by using both migration patterns and latitudinal position. This model demonstrates that the prevalence of MS is influenced by both genetic and environmental contributions.
BACKGROUND: Newfoundland and Labrador, Canada, have been almost exclusively populated by immigrants from southwest England and southeast Ireland. The province's population grew largely by natural increase from 20,000 people in 1835 to half a million at present. Very little interregional migration occurred within the province. This uniquely-populated region and its subsequent founder effect provide the basis to develop models of disease prevalence. OBJECTIVES: To develop a model for the regional prevalence of multiple sclerosis (MS), accounting for settlement patterns and geographic location (latitude). METHODS: All living MS patients with confirmed addresses (438 patients) in the province were mailed a survey requesting their place of birth. Regional prevalences were calculated from a 75% rate of return of the survey. Theoretical regional prevalences were proportionally calculated from the source prevalences of southwest England, southeast Ireland, Scotland and the Channel Islands based on settlement patterns. These theoretical regional prevalences were corrected for geographical variations of latitude based on observations in the United Kingdom. Theoretical and actual regional prevalences were compared. RESULTS: When actual regional prevalences were compared with theoretical prevalences, very little variation was noted, especially after correcting for variation in latitude. CONCLUSION: A regional variation in MS prevalence is noted in the island portion of Newfoundland and Labrador. This regional variation can be modeled by using both migration patterns and latitudinal position. This model demonstrates that the prevalence of MS is influenced by both genetic and environmental contributions.