Epidemiology of multiple sclerosis in US veterans. 6. Population ancestry and surname ethnicity as risk factors for multiple sclerosis.

Previously, we studied the effect of population ancestry on the risk of multiple sclerosis (MS) in US veterans of World War II, comparing by state 1980 US census ancestry data with MS case/control ratios. Here, the joint effects of population ancestry and surname-derived ethnicity on MS risk are examined in the same series. Census data are used again to characterize the population ancestry of the state from which each subject entered active duty (EAD)--that is, the proportions of the populace reporting various ancestries--and subjects were also individually categorized into a single ethnic group, without knowledge of case/control status, based on surname. In this study population, categorized ethnicity was strongly correlated with population ancestry, as expected. Although univariate analyses showed statistically significant associations between MS risk and several surname-derived ethnicities and ethnic groups, when residence at EAD was accounted for as well, there was almost no ethnic variation in MS risk. A logistic regression analysis further showed that variations in MS risk are associated most strongly with latitude and population ancestry group; in particular, subjects who entered military service from states with higher proportions of Swedish or French ancestry had higher risks of MS. After adjustment for characteristics of place, the only significant individual ethnicity factor found was Southern European ethnicity. In general, we conclude that an individual's ethnicity seems to be of less relative importance in determining MS risk than is the population ancestry of the state of EAD. These findings underscore the fact that MS is a disease of place, with 'place' including not only attributes of the locale (e.g., latitude), but also of its populace (e.g., ancestry).