The geographic distribution of Multiple Sclerosis is nonrandom, as the disease is more prevalent in Temperate than in Tropical regions. Surveys conducted between 1970 and 1996 suggest that Multiple Sclerosis is more prevalent in the Northern part of the United Kingdom than in the Southern part.
This North-South gradient ("the Latitudinal gradient") might be a methodological artifact, because high prevalence figures from serial surveys of the Northern part of the United
Kingdom might have been the result of better ascertainment.
By using capture-recapture methods, the authors found that case ascertainment was similar in the Northern and Southern parts of the United Kingdom. When prevalence figures for Multiple Sclerosis in the Southern United Kingdom were increased to account for the number of unobserved cases, the difference persisted:
The prevalence of Multiple Sclerosis in the Northern part of the United Kingdom appeared to be at least 180 cases per 100,000 persons, whereas the maximum prevalence in the Southern part of the United Kingdom was less than 160 cases per 100,000 persons.
The distribution of Multiple Sclerosis in the United Kingdom is not uniform and is consistent with the hypothesis that populations with a high prevalence of Multiple Sclerosis may be Genetically predisposed to the disease.