The geographic association of multiple sclerosis and amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) and multiple sclerosis (MS) are both devastating, incurable, neurodegenerative diseases that are largely considered to be of unknown etiology. While the diseases have some similarities, they are not typically considered to be closely related. They have different pathological markers and different prognoses. Additionally, MS (but not ALS) is considered an autoimmune disease. Furthermore, MS has long been noted to have a strong north-south gradient in its distribution whereas only recently has awareness grown of such a gradient in ALS. The study here will show, however, that if the distribution of ALS and MS are analyzed using mortality data, they are extremely correlated even after controlling for gender, race and latitude. This relationship was not previously identified in part because of a Simpson's paradox in the data: strong correlations that are obvious in the data when they are separated by gender are obscured when the data are pooled across gender. The presence of a strong association in the distributions of ALS and MS suggests there is a connection between the two diseases that is not yet understood. That connection may prove valuable in helping to illuminate what causes the diseases, and whether and how they can be prevented and treated.